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Unit IV: (Structural organisation) Chapter 9 and Tissue System

Learning Objectives The learner will be able to, Nehemiah Grew • Study major types of plant cells and Father of Plant their . Anatomy • Differentiate the various types of 1641–1712 cells. • Study the relationship between the Katherine Esau (1898–1997) distribution of tissues in the various A legendary Role model for women in parts of . science. She was a scintillating • Describes the system teacher and pioneering researcher for [ and ] and vascular six decades. Her classic book Anatomy systems of Plants is the best literature in . In • Interpret cross sections and recognition of her longitudinal sections of dicot and distinguished service monocot , stem and . to science, she was • Compare the internal organization awarded National of dicot root and monocot root. Medal of Science (1989) by USA.

This chapter introduces the internal of higher Plants. The study of Chapter Outline internal structure and organisation of 9.1 Meristematic tissue plant is called plant Anatomy (Gk: Ana = 9.2 Permanent tissues as under; temnein = to cut). Plants have cells as the basic unit. The cells are 9.3 The tissue system organised into tissues. The tissues in turn 9.4 Epidermal tissue system are organised into organs. The different Fundamental tissue system 9.5 organs in a plant have different internal 9.6 system . It is studied by means of 9.7 Comparision of primary structure dissection and microscopic examination.

1 Milestones in Anatomy of tissue is called . A plant is made up of different types of tissues. • 1837 Hartig: Coined the term Sieve tubes There are two principal groups: • 1839 Schleiden: Coined the term 1. Meristematic tissues Collenchyma 2. Permanent tissues • 1857 Hofmeister: Proposed Apical 9.1 Meristematic Tissue theory • 1858 Nageli. C: Coined the term 9.1.1 Characteristics and classification and , and supporter The characters of meristematic tissues: of Apical (Gr. Meristos-Divisible) • 1865 Mettenius: Coined the term The term meristem is coined by Sclerenchyma C. Nageli 1858. • 1868 Hanstein: Proposed Histogen • The meristematic cells are isodiametric theory and they may be, oval, spherical or • 1885 Tschirch: Coined the term polygonal in shape. Named Four types of • They have generally dense Sclereids (Brachy, Macro, Osteo & with prominent nucleus. Astro) in 1889 • Generally the in them are • 1914 Haberlandt: Coined the term either small or absent. xylem as Hadrome and Phloem as Leptome and Classification of • Their is thin, elastic and meristem. essentially made up of . • 1924 Schmidt A: Proposed Tunica – • These are most actively dividing cells. Corpus theory • Meristematic cells are self-perpetuating. • 1926 Schűepp: Mass, rib, & plate meristem Classification of Meristem • 1946 Bloch: Discovered the Meristem has been classified into several Trichosclereids types on the basis of position, origin, • 1952 Popham: Explained the function and division. organization of apex of Apical meristem Angiosperms • 1955 Duchaigne: Discovered the Annular collenchyma Intercalary meristem • 1961 Clowes: Proposed Quiescent centre concept

• 1963 Sanio: Coined the term Lateral meristem The Tissues A Tissue is a group of cells that are alike in Figure 9.1: Different types of origin, structure and function. The study on the basis of position in plant body

2 Classification of Meristem

Position Origin Function Plane of division

Apical meristem Protoderm Mass meristem Present in apices of root Primary It gives rise to It divides in all and shoot. It is responsible Meristem epidermal tissue planes. Example: for increase in the length It is derived system and ,young of the plant, it is called as from develops into and primary growth. embryonic ,stomata stages and and hairs. differentiated into primary Intercalary meristem permanent Occurs between the Rib meristem or tissues. Procambium mature tissues. It is File meristem It gives rise to responsible for elongation It divides primary vascular of internodes. anticlinally in one tissues. Example: Secondary plane. Example: xylem and phloem . meristem It is development of derived during cortex and pith Lateral meristem later stage of Occurs along the development longitudinal axis of stem of the plant Plate meristem and root. It is responsible Ground Meristem It divides for secondary tissues and body. It It gives rise to anticlinally in two thickening of stem and produces all tissues except planes. Example: root. Example: vascular and epidermis and development of cambium and cork interfascicular vascular strands. epidermis cambium. cambium.

Theories of Meristem Organization and Shoot Apical Meristem Function Apical Cell Theory Many anatomists illustrated the root Apical cell theory is proposed by and shoot apical meristems on the basis Hofmeister (1852) and supported by of number and arrangement and accordingly Nageli (1859). A single apical cell is the proposed the following theories – An structural and functional unit. extract of which are discussed below.

Apical cell

Tunica

Leaf primodium Leaf primordia Dermatogen Periblem Histogen Corpus Plerome a. b. c. Figure 9.2: Shoot apical meristem a) Apical cell theory, b) Histogen theory, c) Shoot Tunica corpus theory

3 This apical cell governs the growth at their apices and the apical meristem and development of whole plant body. It is present below the root cap. The is applicable in , and in different theories proposed to explain some . root apical meristem organization is given below. Histogen Theory Apical Cell Theory Histogen theory is proposed by Hanstein Apical cell theory is proposed by (1868) and supported by Strassburgur. The Nageli. shoot apex comprises three distinct zones. The single apical cell or apical initial composes the root meristem. The apical 1. It is a outermost layer. Dermatogen: initial is tetrahedral in shape and produces It gives rise to epidermis. root cap from one side. The remaining 2. Periblem: It is a middle layer. It gives three sides produce epidermis, cortex and rise to cortex. vascular tissues. It is found in vascular 3. Plerome: It is innermost layer. It gives . rise to Histogen Theory Tunica Corpus Theory Histogen theory is proposed by Hanstein Tunica corpus theory is proposed by (1868) and supported by Strassburgur. A. Schmidt (1924). The histogen theory as appilied to the Two zones of tissues are found in apical root apical meristem speaks of four meristem. histogen in the meristem. They are respectively 1. The tunica: It is the peripheral zone of shoot apex, that forms epidermis. i. Dermatogen: It is a outermost layer. It gives rise to root epidermis. 2. The corpus: It is the inner zone of shoot apex,that forms cortex and stele ii. Periblem: It is a middle layer. It gives of shoot. rise to cortex. Root Apical Meristem iii. Plerome: It is innermost layer. It gives Root apex is present opposite to the rise to stele shoot apex. The contain root cap iv. Calyptrogen: It gives rise to root cap.

Epidermis Stele Cortex Cortex Stele Cortex Protoderm

T Ground tissue Quiescent Root centre cap Inverted ‘T’ division (Y division) Cap

Plerome b. Calyptrogen c. Periblem Dermatogen / Calyptrogen Figure 9.3: Root apical meristem a) Histogen Theory, b) Korper kappe theory, Root cap a. c) Quiescent Centre Concept

4 Korper Kappe Theory (Gk: Para-beside; Korper kappe theory is proposed by enehein- to pour) Schuepp. There are two zones in root Parenchyma is generally present in all organs apex – Korper and Kappe of the plant. It forms the ground tissue in a 1. Korper zone forms the body. plant. Parenchyma is a living tissue and made up of thin walled cells. The cell wall is made 2. Kappe zone forms the cap. This theory is equivalent to tunica corpus up of cellulose. Parenchyma cells may be oval, theory of shoot apex.The two divisions polyhedral, cylindrical, irregular, elongated are distinguished by the type of T or armed. Parenchyma tissue normally has (also called Y divisions). Korper is prominent intercellular spaces. Parenchyma characterised by inverted T divisions may store various types of materials like, and kappe by straight T divisions. , air, ergastic substances. It is usually colourless. The turgid parenchyma cells help Quiescent Centre Concept in giving rigidity to the plant body. Partial Quiescent centre concept was proposed conduction of water is also maintained by Clowes (1961) to explain root apical through parenchymatous cells. meristem activity. These centre is located between root cap and differentiating Intercellular spaces cells of the roots. The apparently inactive region of cells in root promeristem is called quiescent centre. It is the site of synthesis and also the ultimate source of all meristematic cells of the meristem.

9.2 Permanent Tissues Figure 9.4: Parenchyma The Permanent tissues develop from apical meristem. They lose the power of cell Occsionally Parenchyma cells which division either permanently or temporarily. store resin, tannins, crystals of calcium They are classified into two types: carbonate, calcium oxalate are called idioblasts. Parenchyma is of different types 1. Simple permanent tissues. and some of them are discussed as follows. 2. Complex permanent tissues. Types of Parenchyma Simple Permanent Tissues Simple tissues are composed of one type grainsg of cells only. The cells are structurally and Intercellular spaces functionally similar. It is of three types. 1. Parenchyma a. b. 2. Collenchyma Types of Parenchyma 3. Sclerenchyma Figure 9.5: a) , b) Storage parenchyma

5 1. Aerenchyma: Parenchyma which contains air in its intercellular spaces. It helps in aeration and buoyancy. Example: Nymphae and Hydrilla.

5. Prosenchyma: 2. Storage Parenchyma: Parenchyma cells became Parenchyma stores food elongated, pointed and slightly Parenchyma materials. Example: Root and thick walled. It provides stem tubers. mechanical support.

4. Chlorenchyma 3. How?.... Stellate Parenchyma cells with Parenchyma . Function is Star shaped parenchyma. . Example: Example: Petioles of Banana Mesophyll of . and Canna.

Intercellular Intercellular small or none. Tannin maybe Space Spaces present in collenchyma.Based on pattern Palisade of pectinisation of the cell wall, there are Parenchyma three types of collenchyma Spongy Parenchyma Types of Collenchyma a. b. c. 1. Angular collenchyma It is the most common type of collenchyma Figure 9.5: c) Stellate parenchyma, with irregular arrangement and d) Chlorenchyma, e) Prosenchyma thickening at the angles where cells meets. Example:Hypodermis of Datura and Collenchyma (Gk. Colla-glue; Nicotiana enchyma – an infusion) Collenchyma is a simple, living mechanical 2. Lacunar collenchyma tissue. Collenchyma generally occurs in The collenchyma cells are irregularly hypodermis of dicot stem. It is absent arranged. Cell wall is thickening on the in the roots and also occurs in petioles walls bordering intercellular spaces. and pedicels. The cells are elongated Example:Hypodermis of Ipomoea and appear polygonal in cross section. The cell wall is unevenly thickened. 3. Lamellar collenchyma It contains more of and The collenchyma cells are arranged pectin besides cellulose. It provides compactly in layers(rows). The Cell wall mechanical support and elasticity to the is thickening is at tangential walls.These thickening appear as successsive tangential growing parts of the plant. Collenchyma layers. Example:Hypodermis of Helianthus consists of narrow cells. It has only a few

6 Diagramatic structures

Nucleus Thickened Intercellular corners thickenings

Vacuole Lamellar Cell wall thickenings

a. b. c. Figure 9.6: Types of Collenchyma a) Angular collenchyma, b) Lacunar collenchyma, c) Lamellar collenchyma

1. Sclereids Duchaigne (1955) Annular Collenchyma: 2. Fibres reported another type called Annular collenchyma in of Nerium. The Sclereids (Stone Cells) lumen is more or less circular in shape. Sclereids are dead cells, usually these are isodiametric but some are elongated Sclerenchyma (Gk. Sclerous- hard: too. The cell wall is very thick due enchyma-an infusion) to lignification. Lumen is very much The sclerenchyma is dead cell and reduced. The pits may simple or branched. lacks protoplasm. The cells are long or Sclereids are mechanical in function. short, narrow thick walled and lignified They give hard texture to the seed coats, secondary walls. The cell walls of these cells etc., Sclereids are classified are uniformly and strongly thickened. The into the following types. sclerenchymatous cells are of two types:

Types of Sclereids

1. Branchysclereids or Stone cells: 2. Macrosclereids: Isodiametric sclereids, with hard cell Elongated and rod shaped cells, found in wall. It is found in , pith cortex, hard the outer seed coat of leguminous plants. endosperm and fleshy portion of some Example: Crotalaria and Pisum sativum. . Example: - Pulp of Pyrus.

3. Osteosclereids ( cells): Rod shaped with dilated ends. They occur in leaves and seed coats. Example: seed coat of Pisum and Hakea

4. Astrosclereids: 5. Trichosclereids: Star cells with lobes or arms diverging Hair like thin walled sclereids. Numerous form a central body. They occur in petioles small angular crystals are embedded in the and leaves. Example: Tea, Nymphae and wall of these sclereids, present in stems and Trochodendron. leaves of hydrophytes. Example: Nymphaea leaf and Aerial roots of Monstera.

7 Diagramatic Structures

Macro Lumen

Lumen cell Thick cell wall Lumen Thick cell wall

Pith a. b. c.

Thick Tricho cell wall Sclereids Lumen

d. e. Figure 9.7: Types of Sclereids a) Brachysclereids, b) MacroSclereids, c) Osteosclereids, d) Astrosclereids, e) Trichosclereids

pits. They provide Pointed end Filiform Sclereids: The sclereids mechanical are present in the leaf of strength and Olea europaea. They are very much protect them elongated fibre like and about 1m.m from the strong length. wind. It is also called supporting Sclerenchyma Found in Some Fruits tissues. Fibres have a great commercial value in cottage and Lumen industries.

Fibres are of five Figure 9.8: a) , types b) Strawberry, c) Guava Figure 9.9 T.S of fibre Fibres or Xylary Fibres Fibres These fibres are associated with the Fibres are very much elongated secondary xylem tissue. They are also sclerenchyma cells with pointed tips. called xylary fibres. These fibres are Fibres are dead cells and have lignified derived from the vascular cambium. walls with narrow lumen. They have simple These are of four types. a. Libriform fibres

8 b. Fibre tracheids c. Septate fibres Mesocarp Fibres d. Gelatinous fibres. Fibres obtained from the mesocarp of like Coconut. Fibres are the longest Leaf Fibres plant cells. Longest Fibres obtained from the leaf of Fibres occur in Musa, Agave and Sensciveria. Boehmeria ( fibre) 55 cm long Fibres in Our Daily Economically fibres may be grouped as a. Libriform fibres: These fibres have follows slightly lignified secondary walls with 1. Fibres utilized for the simple pits. These fibres are long and Textile Fibres: manufacture of fabrics, netting and narrow. cordage etc. b. These are shorter Fibre tracheids: a. : Example: Cotton. than the libriform fibres with moderate Surface Fibres secondary thickenings in the cell walls. b. Soft Fibres: Example: , and Pits are simple or bordered. Ramie c. Example: , c. Septate fibres: Fibres that have thin Hard fibres: septa separating the lumen into distinct Coconut, Pineapple, Abaca etc. chambers. Eg. Teak 2. Brush fibre: Fibres utilized for the manufacture of brushes and brooms. d. Gelatinous fibres: Fibres in which is less in amount and cellulose is more in 3. Rough weaving fibres: Fibres utilized this cell walls. in making baskets, chairs, mats etc. These fibres are characteristic of tension 4. Paper making fibres: Wood fibres wood which is formed in the underside of utilized for paper making. leaning stems and branches. 5. Filling fibres: Fibres used for stuffing cushions, mattresses, pillows, furniture Bastfibres or Extra Xylary Fibres etc. Example: Bombax and Silk cotton. These fibres are present in the phloem. Natural Bast fibres are strong and Complex Tissues cellulosic. Fibres obtaining from the A complex tissue is a tissue phloem or outer bark of jute, kenaf, with several types of cells flax and plants. The so called but all of them function pericyclic fibres are actually phloem together as a single unit. It fibres. is of two types – xylem and phloem. Surface Fibres These fibres are produced from the surface Xylem of the plant organs. Cotton and silk cotton The xylem is the principal water conducting are the examples.They occur in the testa tissue in a . The term xylem of . was introduced by Nageli(1858) and is

9 derived from the Gk. Xylos – wood. The Tracheids xylem which is derived from Procambium is Tracheids are dead, lignified and called primary xylem and the xylem which elongated cells with tapering ends. Its is derived from vascular cambium is called lumen is broader than that of fibres. In secondary xylem. Early formed primary cross section, the tracheids are polygonal. xylem elements are called protoxylem, There are different types of cell wall whereas the later formed primary xylem thickenings due to the deposition of elements are called metaxylem. secondary wall substances. They are Protoxylem lies towards the periphery annular (ring like), spiral (spring like), and metaxylem that lies towards the centre scalariform (ladder like) reticulate (net is called Exarch. It is common in roots. like) and pitted (uniformly thick except Protoxylem lies towards the centre and at pits). Tracheids are imperforated cells meta xylem towards the periphery this with bordered pits on their side walls. condition is called Endarch. It is seen in Only through this conduction takes place stems. in . They are arranged one Protoxylem is located in the centre above the other. Tracheids are chief water surrounded by the metaxylem is called conducting elements in Gymnosperms Centrarch. In this type only one vascular and Pteridophytes. They also offer strand is developed. Example: Selaginella mechanical support to the plants. sp. Protoxylem is located in the centre surrounded by the metaxylem is called Mesarch.In this type several vascular strands are developed. Example: Ophioglossum sp.

Student Activity Annular Spiral Reticulate Scalariform Pitted thickening students prepare the slide Cell lab: Figure 9.10: Types of secondary wall and identify the different types tissues. thickenings in tracheids and vessels

Xylem Consists of Four Types of Cells Vessels or Trachea 1. Tracheids Vessels are elongated tube like structure. 2. Vessels or Trachea They are dead cells formed from a row of 3. Xylem Parenchyma vessel elements placed end to end. They 4. Xylem Fibres are perforated at the end walls. Their lumen is wider than Tracheids. Due to Xylem is called hadrome phloem the dissolution of entire cell wall, a single is called leptome. These terms are pore is formed at the perforation plate. coined by haberlandt (1914) It is called simple perforation plate, Example: Mangifera. If the perforation

10 plate has many pores, it is called multiple Xylem Parernchyma perforation plate. Example Liriodendron. The parenchyma cells associated with the The secondary wall thickening of xylem are known as xylem parenchyma. vessels are annular, spiral, scalariform, These are the only living cells in xylem reticulate, or pitted as in tracheids, Vessels tissue. The cell wall is thin and made are chief water conducting elements in up of cellulose. Parenchyma arranged Angiosperms and absent in Pteridophytes longitudinally along the long axis is called and Gymnosperms. In Gnetum of axial parenchyma. Ray parenchyma is , vessels occur. The main arranged in radial rows. Secondary xylem function is conduction of water, minerals consists of both axial and ray parenchyma, and also offers mechanical strength. Parenchyma stores food materials and also helps in conduction of water. Xylem Fibre The fibres of sclerenchyma associated Phloem with the xylem are known as xylem fibres. Phloem is the food conducting complex Xylem fibres are dead cells and have tissues of vascular plants. The term lignified walls with narrow lumen. They phloem was coined by C. Nageli (1858) cannot conduct water but being stronger The Phloem which is derived from provide mechanical strength. They are procambium is called primary phloem and present in both primary and secondary the phloem which is derived from vascular xylem. Xylem fibres are also called cambium is called secondary phloem. libriform fibres. Early formed primary phloem elements The fibres are abundantly found in many are called protophloem whereas the later plants. They occur in patches, in continuous formed primary phloem elements are bands and sometimes singly among other called metaphloem. Protophloem is short cells. Between fibres and normal tracheids, lived. It gets crushed by the developing there are many transitional forms which are metaphloem. neither typical fibres nor typical tracheids. The transitional types are designated as Phloem Consists of Four Types of Cells fibre-tracheids. The pits of fibre-tracheids 1. Sieve elements are smaller than those of vessels and typical 2. Companion cells tracheids. 3. Phloem parenchyma

Vessels are found in 4. Phloem fibres Gymnosperms like Sieve Elements Ephedra, Gnetum and Sieve elements are the conducting Welwitschia elements of the phloem. They are of two Vesselless angiospermic families types, namely sieve cells and sieve tubes. Winteraceae, Tetracentraceae and Trochodendracae. Sieve Cells These are primitive type of conducting

11

Concept Map Plant tissues

Meristematic tissue: Permanent tissues: Capable of active cell division. Lose the power of cell division. Thin walled and living. Have definite shape, size and form. Compactly arranged. Found in root and shoot apex. Simple tissues: Complex tissues: One type of cells. More than one type Based on position: of cells. 1. Apical 2. Intercalary Parenchyma: 3. Lateral Thin walled,isodiametric, found in all the parts. Xylem: Water Types: conducting tissue. Based on origin: 1. Aerenchyma. 1. Tracheids: Dead, 2. Storage parenchyma. elongated with 1. Primary 3. Stellate parenchyma. tapering end 2. Secondary 4. Chlorenchyma. 2. Vessels: Made of 5. Prosenchyma. row of dead cells 3. Xylem fibres: Based on function: Lignified and 1. Periderm (Epidermis ) Collenchyma: sclerenchymatous. 2. Procambium (Primary Hypodermal position. Provide 4. Xylem vascular tissues) mechanical strength. parenchyma: 3. Ground meristem (Cortex Types: Living and and Pith) 1. Angular collenchyma. cellulosic 2. Lacunar collenchyma. 3. Lamellar collenchyma. Based on division: 1. Mass meristem: Divides in all Phloem: Food Sclerenchyma: Dead cells and planes conducting tissue lignified walls. 1. Sieve elements: Sieve 2. Rib meristem: Anticlinal Types: division in one plane cells & sieve tubes 1. Sclereids 2. Companion cells: 3. Plate meristem: Anticlinal 2. Fibres division in two planes. Only in Angiosperms. 3. Phloem parenchyma: Sclereids: 1. Brachysclereids: Stone cells Living & absent in 2. Macro sclereids: Rod shaped Monocots. 3. Osteosclereids: Bone shaped 4. Phloem fibres: Syncyte: Cell Thick walled & which is formed 4. Astrosclereids: Star shaped 5. Trichosclereids: Hair cells sclerenchymatous, by fusion of giving mechanical c e l l i s c a l l e d strength. Syncyte. Fibres: Vessels (Dead 1. Wood fibres xylary fibres Example: 2. Bastfibres: Extra xylary fibres syncyte), sieve tube (living 3. Surface fibres: Cottan syncyte) 4. Mesocarp fibres: Ccoconut 5. Leaf fibres: Musa, Agave

13 Table 9.1: Different types of tissues Distribution Main functions Cell shape Wall materials Parenchyma Cortex, Pith Packing tissue, Living Usually Mainly medullary rays support, gaseous Isodiametric Cellulose and and Packing exchange, food Pectinase tissues in storage vascular system Collenchyma Outer region Mechanical Living Elongated, Mainly of cortex as in Polygonal Cellulose, angles of stems, Pectin and mid-rib of leaves Hemi-cellulose Sclerenchyma Outer region of Mechanical Dead Elongated Mainly Lignin (a) Fibre cortex, and of stems, vascular Polygonal bundles with tapering ends (b) Sclereids Cortex, Pith, Mechanical Dead Roughly Mainly lignin Phloem shells Protection Isodiametric and stones of with much fruits and seed variation coats Tracheids and Vascular System Translocation Dead Elongated Mainly lignin Vessels of water and and Tubular mineral salts Phloem Sieve Vascular System Translocation of Living Elongated Cellulose, tubes organic solutes and Tubular Pectin and Hemicellulose Companion Vascular System Work in Living Elongated Cellulose, Cells association with and narrow Pectin and sieve tubes Hemicellulose

Difference Between Meristematic Tissue and Permanent Tissue Meristematic tissue Permanent tissue • Cells divide repeatedly • Do not divide • Cells are undifferentiated • Cells are fully differentiated • Cells are small and Isodiametric • Cells are variable in shape and size • Intercellular spaces are absent • Intercellular spaces are present • Vacuoles are absent • Vacuoles are present • Cell walls are thin • Cell walls maybe thick or thin • Inorganic inclusions are absent • Inorganic inclusions are present

14 Difference Between Collenchyma and Sclerenchyma Collenchyma Sclerenchyma • Living Cells • Dead cells • Contains Protoplasm • Cells are empty • Cell walls are cellulosic • Cell walls are lignified • Thickening of cell wall is not uniform • Thickening of cell wall is uniform • Keeps the plant body soft • Keeps plant body stiff and hard • Sometimes it has chloroplast • Do not have chloroplast

Difference between Fibre and Sclereids Fibre Sclereids • Long cells • Short cells • Narrow, Elongated pointed ends • Usually short and broad • Occurs in bundles • Occurs individually or in small groups • Commonly unbranched • Maybe branched • Derived directly from meristematic • Develops from secondary sclerosis tissue parenchyma cells

Difference between Tracheids and Fibres Tracheids Fibres • Not much elongated • Very long cells • Possess oblique end walls • Possess tapering end walls • Cell walls are not as thick as Fibres • Cell wall are thick and lignified • Possess various types of thickenings • Possess only pitted thickenings • Responsible for the conduction and also • Provide only mechanical support mechanical support

Difference Between Sieve Cells and Sieve Tubes Sieve cells Sieve tubes • Have no companion cells • Have companion cells • The sieve areas do not form sieve plates • The sieve areas are confined to sieve • The sieve areas are not well plates differentiated • The sieve areas are well differentiated • They are elongated cells and are quite • They consist of vertical cells placed long with tapering end walls one above the other forming long tubes • The sieve are smaller and numerous connected at the walls by sieve pores • Found in Pteridophytes and • The sieve pores are longer and fewer Gymnosperms • Found in Angiosperms

15 9.3 The Tissue System recognized three tissue systems in the plants. They are: Introduction to Tissue System, Types and Characteristics of tissue System 1. Epidermal tissue system (derived from protoderm) As you have learnt, the plant cells are organised into tissues, in turn the tissues 2. Ground tissue system (derived from are organised into organs. Different ground meristem) organs in a plant show differences in their 3. Vascular tissue system (derived from internal structure. This part of chapter procambium) deals with the different type of internal structure of various plant organs and its to diverse environments. Histology A group of tissues (Greek. histos – web, performing a similar logos – science) It is function, irrespective of the study of tissues, its position in the plant their composition, and structure as observed with the help of body, is called a tissue . system. In 1875, German Figure 9.12: Scientist Julius von Sachs Julius von Sachs

Figure 9.13: Tissue system

16 Table 9.2: Types and characteristics of tissue systems S.No. Types/ Epidermal tissue Ground or Vascular or Characters system fundamental tissue conduction tissue system system 1. Formation Forms the outermost Forms the ground Forms the covering protoderm meristem procambial bundles 2. Components epidermal Simple permanent Xylem and Phloem cells, stomata tissues – and epidermal Parenchyma and outgrowths Collenchyma 3. Functions Protection of plant Gives mechanical Conducts water body; absorption support to the and food; gives of water in roots; organs; prepares and mechanical strength for stores food in leaf photosynthesis and stem and ; in

9.4 Epidermal Tissue System Stem Epidermis Introduction It is protective in function and forms the outermost layer of the stem. It is a single is the outer most Epidermal tissue system layer of parenchymatous rectangular cells. covering of plants. It is in direct contact The cells are compactly arranged without with external environment. It consists intercellular cells. The outer walls of of epidermis derived from protoderm. epidermal cells have a layer called . Epidermis is derived from two Greek words, cuticle The cuticle checks . The namely ‘Epi’ and ‘Derma’. ‘Epi’ means transpiration cuticle is made up of . In many plants and ‘Derma’ means . Although cutin upon it is also mixed wax to form epicuticular epidermis is a continuous outer layer, it is wax. Epidermal pores may be present interrupted by stomata in many plants. here and there. Epidermal cells are living. Chloroplasts are usually absent except in Root Epidermis guard cells of stomata. In many plants a The outer layer of the root is known as large number of epidermal hairs occur on It is made up piliferous layer or epiblema. the epidermis. of single layer of parenchyma cells which are arranged compactly without intercellular Leaf Epidermis spaces. It is devoid of epidermal pores and The leaf is generally . It has cuticle. Root hair is always single celled, it dorsiventral upper and lower epidermis. The epidermis absorbs water and mineral salts from the is usually made up of a single layer of cells soil. The another important function of that are closely packed. Generally the piliferous layer is protection.

17 cuticle on the upper epidermis is thicker epidermal cells called guard cells. In most than that of lower epidermis. The minute dicots and monocots the guard cells are openings found on the epidermis are bean-shaped. While in grasses and sedges, called stomata (singular: ). Usually, the guard cells are dumbbell- shaped. The stomata are more in number on the lower guard cells contain chloroplasts, whereas epidermis than on the upper epidermis. A the other epidermal cells normally do not stoma is surrounded by a pair of specialised have them.

Subsidiary cell

Figure 9.14: (a) Stoma with bean-shaped guard cells. (b) Stoma with dumb-bell shaped guard cells

Some cells of upper epidermis mainly in the epidermis of leaves. In (Example: Grasses) are larger and thin some plants addition to guard cells, walled. They are called bulliform cells specialised epidermal cells are present or motor cells. These cells are helpful which are distinct from other epidermal for the rolling and unrolling of the leaf cells. They are called Subsidiary cells. according to the weather change. Some Based on the number and arrangement of the epidermal cells of the grasses are of subsidiary cells around the guard filled with silica. They are called silica cells, the various types of stomata cells. are recognised. The guard cells and subsidiary cells help in opening and Check Your Grasp! closing of stomata during gaseous In which group of plants the guard exchange and transpiration. cells are dumb-bell shaped? Sunken Stomata Grasses and sedges In some Xerophytic plants (Examples: Cycas, Nerium), stomata is sunken beneath the abaxial leaf surface within stomatal Subsidiary Cells crypts. The sunken stomata reduce water Stomata are minute pores surrounded loss by transpiration. by two guard cells. The stomata occur

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Prickles main zones – cortex, pericycle and pith. Prickles, are one type of It is classified into extrastelar ground epidermal emergences tissue (Examples: cortex and endodermis) with no vascular supply. and intrastelar ground tissue (Examples: They are stiff and sharp pericycle, medullary ray and pith) in appearance. (Example: Extrastelar Ground Tissue Rose). The ground tissues present outside the Figure 9.17: Functions of Epidermal stele is called extrastelar ground tissue. Prickles Tissue System (Cortex) 1. This system in the shoot checks Intrastelar Ground Tissue excessive loss of water due to the The ground tissues present within the presence of cuticle. stele are called intrastelar ground tissues. 2. Epidermis protects the underlying (pericycle, medullary rays and pith). tissues. 3. Stomata is involved in transpiration Different Components of Ground and gaseous exchange. Tissue Systems are as follows 4. are also helpful in the Hypodermis dispersal of seeds and fruits, and One or two layers of continuous or provide protection against . discontinuous tissue present below the 5. Prickles also provide protection against epidermis, is called hypodermis. It is animals and they also check excessive protective in function. transpiration In dicot stem, hypodermis is generally 6. In some rose plants they also help in collenchymatous, whereas in monocot climbing. stem, it is generally sclerenchymatous. 7. Glandular hairs repel herbivorous In many plants collenchyma form the animals. hypodermis. General Cortex 9.5 Fundamental Tissue System The Cortex occurs between the epidermis The ground or fundamental tissue system and pericycle. Cortex is a few to many constitutes the main body of the plants. It layers in thickness, In most cases, it is includes all the tissues except epidermis made up of parenchymatous tissues. and vascular tissues. In monocot stem, Intercellular spaces may or may not be ground tissue system is a continuous present. mass of parenchymatous tissue in which The cortical cells may contain non vascular bundles are found scattered. living inclusions of starch grains, oil, Hence ground tissue is not differentiated tannins and crystals. into cortex, endodermis, pericycle and Sometimes in young stem, chloroplasts pith. Generally in dicot stem, ground develop in peripheral cortical cells, which tissue system is differentiated into three is called chlorenchyma.

20 In the leaves, the ground tissue consists Pericycle of chlorenchyma tissues. This region is Pericycle is single or few layered parenchymatous called mesophyll. In hydrophytes, cortex is found inner to the endodermis. It is the Aerenchymatous (with air cavities). outermost layer of the stele. Rarely thick walled Its general function is storage of food sclerenchymatous. In angiosperms, pericycle as well as providing mechanical support gives rise to lateral roots. to organs. Pith or Medulla Endodermis The central part of the ground tissue is The cells of this layer are barrel shaped and known as pith or medulla. Generally this arranged compactly without intercellular is made up of thin walled parenchyma spaces. cells with intercellular spaces. The cells Endodermis is the innermost cortical in the pith generally stores starch, fatty layer that separates cortex from the stele. substances, tannins, phenols, calcium This layer may be a true endodermis as in oxalate crystals, etc. root or it is an endodermis like layer in stems. This layer is morphologically homologous Albuminous Cells: The cytoplasmic to the endodermis found in the root. nucleated parenchyma, is associated The cells of endodermis like layer with the sieve cells of Gymnosperms. had living cells containing starch grains. Albuminous cells in Conifers are Hence it is known as starch sheath. In analogous to companion cells of true root endodermis, radial and inner Angiosperms. It also called as tangential walls of endodermal cells strasburger cells. possess thickenings of lignin, suberin and in the form of some other 9.6 Vascular Tissue System strips they are called casparian strips. This section deals with the vascular tissue The endodermal cells, which are opposite to the protoxylem elements, system of gymnosperms and angiosperms are thin walled without casparian strips. stems and roots.The vascular tissue system consists of xylem and phloem. The These cells are called passage cells. Their function is to transport water and elements of xylem and phloem are always dissolved salts from the cortex to the organized in groups. They are called protoxylem. vascular bundles. Water cannot pass through other The stems of both groups have an endodermal cells due to casparian strips. eustele while roots are protostele. In The main function of casparian strips eustelic organization, the stele contains in the endodermal cells is to prevent the usually a ring of vascular bundles separated re-entry of water into the cortex once by interfascicular region or medullary ray water entered the xylem tissue. The structural and organizational The other suberized cells acts as variation in vascular bundles is shown water-tight layer between vascular and non- below. vascular regions to check the loss of water.

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Types of vascular Bundles

Radial Conjoint Concentric

Xylem and phloem are present on Xylem and phloem Xylem and phloem are different radii alternating with each are present on the present in concentric other. The bundles are separated same radius in one circles one around the by parenchymatous tissue. bundle. ( All stems ) other in some stems. (Monocot and Dicot roots)

Collateral Bicollateral

Xylem placed towards inside Phloem occurs on both the and phloem towards outside outer and inner sides of xylem Example: Cucurbitaceae

Open Closed

Amphicribral/Hadrocentric Amphivasal/Leptocentric Cambium is present Cambium is between xylem and absent between phloem. (Stems of xylem and Xylem lies in the centre Phloem lies in the centre Dicots and with phloem surrounding Gymnosperms) phloem. with xylem surrounding it. it. Example: Stems of Example: Dragon plant- Monocots) (Polypodium) dicots and aquatic Dracena and angiosperms

Table 9.3: Comparison of vascular tissues Proto xylem Meta xylem • First formed primary xylem • Later formed primary xylem • Found in developing organs • Found in developed primary organs • Elements relatively smaller in size • Elements relatively larger in size Proto phloem Meta phloem • First formed primary phloem • Later formed primary phloem • Found in developing organs • Found in developed primary organs • Elements relatively smaller in size • Elements relatively larger in size Primary xylem Secondary xylem • The primary xylem is derived from the • The secondary xylem is derived from procambium of the apical meristem the vascular cambium which is a lateral meristem Primary phloem Secondary phloem • The primary phloem is derived from the • The secondary phloem is derived from procambium of the apical meristem the vascular cambium, which is a lateral meristem

23 9.7 Comparison of Primary of the cortex is endodermis. Endodermis Structure – Dicot and Monocot is made up of single layer of barrel shaped parenchymatous cells. Stele is completely Root, Stem and Leaf surrounded by endodermis. The radial and Anatomy of Dicot and Monocot Roots the inner tangential walls of endodermal In different parts of the plants, the various cells are thickened with suberin and lignin. tissues are distributed in characteristic This thickening was first noted by Robert patterns. This is best understood by studying Casparay in 1965. So these thickenings are their internal structure by cutting sections called casparian strips. But these casparian (transverse or longitudinal or both) of the strips are absent in the endodermis cells part to be studied. which are located opposite the protoxylem elements. These thin-walled cells without Primary Structure of Dicot Root – casparian strips are called passage cells Bean Root through which water and mineral salts are The transverse section of the dicot root conducted from the cortex to the xylem (Bean) shows the following plan of elements. Water cannot pass through other arrangement of tissues from the periphery endodermal cells due to the presence of to the centre. casparian thickenings.

Piliferous Layer or Epiblema Check Your Grasp! The outermost layer of the root is called Give the exact location and function piliferous layer or epiblema. It is made up of passage cells? of single layer of parenchyma cells which are In roots some cells of the arranged compactly without intercellular endodermis usually the ones opposite spaces. It is devoid of epidermal pores and to protoxylem, remain thin walled. cuticle. It possesses root hairs which are These cells are called passage cells. single celled. It absorbs water and mineral They help in radial of water. salts from the soil. The chief function of piliferous layer is protection. Stele Cortex All the tissues present inside endodermis Cortex consists of only parenchyma comprise the stele. It includes pericycle cells. These cells are loosely arranged and vascular system. with intercellular spaces to make gaseous Pericycle exchange easier. These cells may store food Pericycle is generally a single layer of reserves. The cells are oval or rounded in parenchymatous cells found inner to the shape. Sometimes they are polygonal due endodermis. It is the outermost layer to mutual pressure. Though chloroplasts of the stele. Lateral roots originate from are absent in the cortical cells, starch the pericycle. Thus, the lateral roots are grain are stored in them. The cells also endogenous in origin. possess leucoplasts. The innermost layer

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Cortex transport water and dissolved salts from The cortex is homogenous. i.e. the cortex the cortex to the xylem. Water cannot is made up of only one type of tissue called pass through other endodermal cells due parenchyma. It consists of many layers to casparian strips. The main function of of thin-walled parenchyma cells with casparian strips in the endodermal cells is lot of intercellular spaces. The function to prevent the re-entry of water into the of cortical cells is storage. Cortical cells cortex once water entered the xylem tissue. are generally oval or rounded in shape. Chloroplasts are absent in the cortical Stele cells, but they store starch. The cells All the tissues inside the endodermis comprise the stele. This includes pericycle, are living and possess leucoplasts. The inner layer of the cortex is endodermis. vascular system and pith. It is composed of single layer of barrel shaped parenchymatous cells. This forms Pericycle a complete ring around the stele. There Pericycle is the outermost layer of the is a band like structure made of suberin stele and lies inner to the endodermis. It and lignin present in the radial and inner consists of single layer of parenchymatous tangential walls of the endodermal cells. cells. They are called casparian strips named after casparay who first noted the strips. Vascular System The endodermal cells, which are opposite Vascular tissues are seen in radial the protoxylem elements, are thin walled arrangement. The number of protoxylem without casparian strips. These cells are groups is many. This arrangement of called passage cells. Their function is to xylem is called polyarch. Xylem is in

Anatomical differences between dicot root and monocot root S.No. Characters Dicot root Monocot root 1. Pericyle Gives rise to lateral roots, Gives rise to lateral roots phellogen and a part of only. vascular cambium. 2. Vascular tissue Usually limited number of Usually more number of xylem and phloem strips. xylem and phloem strips, 3. Conjunctive Parenchymatous; Its cells are Mostly sclerenchymatous tissue differentiated into vascular but sometimes cambium. parenchymatous. It is never differentiated in to vascular cambium. 4. Cambium It appears as a secondary It is altogether absent. meristem at the time of . 5. xylem Usually tetrach Usually polyarch

26 exarch condition, the tissue which is Inner to the hypodermis, a few layers present between the xylem and the of collenchyma cells are present. This zone phloem, is called conjunctive tissue. In is called hypodermis. It gives mechanical maize, the conjunctive tissue is made up strength to the stem. These cells are living of sclerenchymatous tissue. and thickened at the corners. Inner to the hypodermis, a few layers of chlorenchyma Pith cells are present with conspicuous The central portion is occupied by a large intercellular spaces. This region performs pith. It consists of thin-walled parenchyma photosynthesis. Some resin ducts also cells with intercellular spaces. These cells occur here. The third zone is made up of are filled with abundant starch grains. parenchyma cells. These cells store food materials. The innermost layer of the cortex Anatomy of Dicot and Monocot Stems is called endodermis. The cells of this layer The transverse section of the dicot stem are barrel shaped and arrange compactly [sunflower] shows the following plan of without intercellular spaces. Since starch arrangement of tissues from the periphery grains are abundant in these cells, this to the centre. layer is also known a starch sheath. This layer is morphologically homologous Epidermis to the endodermis found in the root. In It is protective in function and forms the most of the dicot stems, endodermis with outermost layer of the stem. It is a single casparian strips is not developed. layer of parenchymatous rectangular cells. The cells are compactly arranged without Check Your Grasp! intercellular spaces. The outer walls of Why the endodermis in dicot stem is epidermal cells have a layer called cuticle. also referred to as the starch sheath? The cuticle checks the transpiration. The The cells of the endodermis are cuticle is made up of waxy substance rich in starch grains and thus this layer known as cutin. Stomata may be present is also referred to as the starch sheath. here and there. Epidermal cells are living. Chloroplasts are usually absent. A large number of multicellular hairs occur on Stele the epidermis. The central part of the stem inner to the endodermis is known as stele. It consists Cortex of pericyle, vascular bundles and pith. In Cortex lies below the epidermis. The dicot stem, vascular bundles are arranged cortex is differentiated into three zones. in a ring around the pith. This type of stele Below the epidermis, there are few layers is called eustele. of collenchyma cells. This zone is called hypodermis. It gives mechanical strength Pericycle of the Stem. These cells are living and Pericycle is the layers of cells that occur thickened at the corners. between the endodermis and vascular bundles. In the stem of sunflower

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Table 9.4: Anatomical differences between dicot stem and monocot stem S.No. Characters Dicot Stem Monocot Stem 1. Hypodermis Collenchymatous Sclerenchymatous 2. Ground tissue Differentiated into cortex, Not differentiated, but it endodermis and pericycle is a continuous mass of and pith parenchyma. 3. Starch Sheath Present Absent 4. Medullary rays Present Absent 5. Vascular (a) Collateral and open (a) Collateral and closed bundles (b) Arranged in a ring (b) Scattered in ground tissue (c) Secondary growth occurs (c) Secondary growth usually does not occur.

Table 9.5: Anatomical differences between root and stem S.No. Characters Root Stem 1. Epidermis Absence of cuticle and Presence of cuticle and epidermal pores. epidermal pores. Presence of unicellular root Presence of unicellular and hairs. multicellular trichomes 2. Outer Cortical Chlorenchyma absent Chlorenchyma present cells 3. Endodermis Well defined ill-defined or absent. 4. Vascular Radial arrangement Conjoint arrangement bundles 5. Xylem Exarch Endarch

Anatomy of a Dicot and Monocot Leaves In dorsiventral leaves the mesophyll Leaves are very important vegetative is differentiated into palisade and spongy organs. They are mainly concerned with parenchyma, the former occurring on the upper side and the later on the lower side photosynthesis and transpiration. Like stem and roots, leaves also have the Example: Sunflower. In isobilateral leaf three tissue system – dermal, ground palisade is present on both sides of the leaf and vascular. The dermal tissue system and inbetween them spongy parenchyma consists of an upper and lower epidermis. is present. Example: Nerium. In some The ground tissue system that lies between plants Example: Ficus calcium crystals the epidermal layers of leaf is known as are present. There are also leaves where spongy tissue alone is present in some mesophyll tissue. Often it is differentiated epidermal cells Example: Grasses. into palisade parenchyma on the adaxial (upper) side and spongy parenchyma on The presence of air spaces is a special the abaxial (lower) side. feature of spongy cells. They facilitate the

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Collateral and closed. Xylem is present Xylem consists of metaxylem and towards the upper epidermis, while the protoxylem elements. Protoxylem is phloem towards the lower epidermis. present towards the upper epidermis,while Vascular bundles are surrounded by the phloem consists of sieve tubes, a compact layer of parenchymatous companion cells and phloem parenchyma. cells called bundle sheath or border Phloem fibres are absent. Xylem consists of parenchyma. vessels and xylem parenchyma. Tracheids and xylem fibres are absent.

Cuticle Upper epidermis Palisade parenchyma Protoxylem Metaxylem Spongy parenchyma Phloem Bundle sheath Stoma Epidermal hair Lower epidermis Respiratory cavity

Figure 9.24: T.S. of Dicot Leaf (Sunflower)

Anatomy of a Monocot Leaf – Grass Leaf These cells are called subsidiary cells. A transverse section of a grass leaf reveals Some cells of upper epidermis are large the following internal structures. and thin walled. They are called bulliform cells or motor cells. These cells are helpful Epidermis for the rolling and unrolling of the leaf The leaf has upper and lower epidermis. according to the weather change. They are made up of a single layer of thin Some of the epidermal cells of the walled cells. The outer walls are covered grass are filled with silica. They are called by thick cuticle. silica cells. The number of stomata is more or less equal on both the epidermis. The stomata Mesophyll is surrounded by dumb – bell shaped The ground tissue that is present between guard cells. The guard cells-contain the upper and lower epidermis of the leaf chloroplasts, whereas the other epidermal is called mesophyll. Here, the mesophyll cells do not have them. is not differentiated into palisade and Some special cells surround the spongy parenchyma. All the mesophyll guard cells. They are distinct from other cells are nearly isodiametric and thin epidermal cells. walled. These cells are compactly arranged

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Differences Between Stomata and Halophiles Hydathodes • Plants that grow in salty environment are called Halophiles. Stomata Hydathodes • Plant growth in saline developed Occur in epidermis Occur at the tip or numerous adaptations to salt stress. of leaves, young margin of leaves The of ions by salt is the stems. that are grown in best known mechanism for regulating moist shady place. the salt content of plant shoots. • Salt glands typically are found in Stomatal aperture Aperture of halophytes. (Plants that grow in saline is guarded by two hydathodes are environments) guard cells. surrounded by a ring of cuticularized cells. The two guard Subsidiary cells cells are generally are absent. surrounded by subsidiary cell. Opening and closing Hydathode pores of the stomatal remain always aperture is regulated open. by guard cells. These are involved These are involved in transpiration and in guttation. exchange of gases. Figure 9.26: Halophytes

Can mangroove grow in salt water? These amazing trees and cope with salt. Salt water can kill Plants, so mangroves must extract fresh water from the sea water that surrounds them. Many mangrove species survive by filtering out as much as 90 percent of the salt found in seawater as it enters their roots. Mangrove excrete salt through glands in their leaves. Figure 9.27: Removes excess salts through special salt glands on leaves

34 Summary root, xylem is tetrach. Its phloem patch consists of sieve tubes, companion cells A Tissue is a group of cells that are alike in and phloem parenchyma. In monocot origin, structure and function.There are two (Example: maize) root, xylem is polyarch. principal groups: (1) Meristematic tissues and (2) Permanent tissues. Meristematic In dicot (Example: sunflower) stem, tissues comprise of self-perpetuating cells. stele is eustele type and its vascular Meristems are classified into several types bundles are wedge shaped, conjoint, on the basis of position, origin, function collateral, open and endarch. In monocot and activity. Many anatomists illustrated stem (Example: maize) vascular bundles the root and shoot apical meristems on are scattered and skull shaped, conjoint, the basis of the type and arrangement and collateral, closed and endarch. accordingly proposed many theories. The In dicot (Example: sunflower) and permanent tissues normally develop from monocot (Example: grass) leaves vascular apical meristem. They are classified into bundles are conjoint, collateral and closed. two types: 1)Simple permanent tissues Hydathodes discharge liquid water and 2)Complex permanent tissues. Simple with various dissolved substances from tissues are composed of a single type of cells the interior of the leaf to its surface. Plants only. It is of three types: (1) Parenchyma that grow in salty environment are called (2) Collenchyma and (3) Sclerenchyma. A halophiles. Salt glands typically are found complex tissue is a tissue with several types in halophytes. of cells but all of them function together as a single unit. It is of two types – xylem and phloem. Secretory tissues produce different Evaluation types of chemicals. Some are in the form of 1. Refer to the given figure and select , , rubber, gum etc. the correct statement The tissues can be classified on the basis of their function, structure and location into epidermal tissue system, ground A B tissue system and vascular tissue system. C Epidermal tissue system develops as the outermost covering of the entire plant body. It consists of epidermal cells and i. A, B, and C are histogen of shoot associated structures. All tissues except apex epidermis and vascular tissues constitute ii. A Gives rise to medullary rays. the ground tissue. The vascular tissue system is formed of vascular bundles. iii. B Gives rise to cortex iv. C Gives rise to epidermis In the primary structure, the outermost layer of the root is called piliferous layer. a. i and ii only Cortex consists of only parenchyma cells. b. ii and iii only All the tissues present inside endodermis c. i and iii only comprise the stele. In dicot (Example: bean) d. iii and iv only

35 2. Read the following sentences and 5. is successful in dicots but identify the correctly matched not in monocots because the dicots sentences. have i. In exarch condition, the a. Vascular bundles arranged in a ring protoxylem lies outside of b. Cambium for secondary growth metaxylem. c. Vessels with elements arranged end ii. In endarch condition, the to end protoxylem lie towords the centre. d. iii. In centarch condition, metaxylem 6. Why the cells of sclerenchyma and lies in the middle of the tracheids become dead? protoxylem. 7. Explain sclereids with their types. iv. In mesarch condition, protoxylem 8. What are sieve tubes ?explain. lies in the middle of the metaxylem. 9. Distinguish the anatomy of dicot root a. i, ii and iii only from monocot root. b. ii, iii and iv only 10. Distinguish the anatomy of dicot stem c. i, ii and iv only from monocot stem. d. All of these 3. In Gymnosperms, the activity of sieve tubes are controlled by a. Nearby sieve tube members. b. Phloem parenchyma cells c. Nucleus of companion cells. d. Nucleus of albuminous cells. 4. When a leaf trace extends from a in a dicot stem, what would be the arrangement of vascular tissues in the veins of the leaf? a. Xylem would be on top and the phloem on the bottom b. Phloem would be on top and the xylem on the bottom c. Xylem would encircle the phloem d. Phloem would encircle the xylem

36 t ICT Corner Plant and Tissues

Let’s explore Plant tissues.

Steps • Scan the QR code or go to Google play store • Type online labs and install it. • Select biology and select plant and animal tissues • Click free sign up and provide your basic information with valid mail-Id • Login with your registered mail id and password • Choose theory tab to know the basic about anatomical structure • Choose animation to view the sectioning process

Activity • Choose simulation tab and view the section of plant parts under microscope

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37 Chapter 10 Secondary Growth

We have studied in the previous chapters Learning Objectives the primary internal structure of monocots The students should be able to, and dicots. If you look at the stem of grass (monocot), it is soft , whereas in the neem • Analyze primary and secondary (dicot), the stem is very hard and woody, growth. why? It is the secondary growth which • Discuss the increase confers the hardness to wood of dicot stems in length and width and roots. In monocots, usually there is no of the plant. secondary growth and so they are soft . • Explain secondary The increase in girth is called growth in dicot stems. secondary growth or growth in girth and • Understand the use of wood we shall discuss the details of secondary products to lead comfortable life. growth in this chapter. • Explain secondary growth in dicot Th e plant organs originating from the roots. apical meristems pass through a period • Discuss anomalous secondary of expansion in length and width. Th e growth in dicots and monocots. roots and stems grow in length with the • Explain the seasoning, grain, help of apical meristems. Th is is called texture and figure of wood. primary growth or longitudinal growth. Th e gymnosperms and most angiosperms, Chapter Outline including some monocots, show an increase 10.1 Secondary Growth in Dicot Stem in thickness of stems and roots by means of 10.2 Secondary Growth in Dicot Root secondary growth or latitudinal growth. The secondary growth in dicots and Anomalous Secondary Growth 10.3 gymnosperms is brought about by two 10.4 Timber lateral meristems. How do the trees increase their girth? • Vascular Cambium and • Cork Cambium

Activity Generally monocots do not have secondary growth, but palms and bamboos have woody stems. Find the reason. Figure 10.1: Taxus wood

38 10.1 Secondary Growth in Dicot Stem The cells of vascular cambium do not fit into the usual description of meristems Vascular Cambium which have isodiametric cells, with a dense The vascular cambium is the lateral cytoplasm and large nuclei. While the active meristem that produces the secondary vascular cambium possesses cells with large vascular tissues. i.e., secondary xylem and central (or vacuoles) surrounded secondary phloem. by a thin, layers of dense cytoplasm. Further, the most important character Origin and Formation of Vascular of the vascular cambium is the presence Cambium of two kinds of initials, namely, fusiform A strip of vascular cambium that is initials and ray initials. believed to originate from the procambium is present between xylem and phloem of Fusiform Initials the vascular bundle. This cambial strip is These are vertically elongated cells. They known as intrafascicular or fascicular give rise to the longitudinal or axial cambium. In between the vascular system of the secondary xylem (treachery bundles, a few parenchymatous cells of elements, fibers, and axial parenchyma) the medullary rays that are in line with the and phloem (sieve elements, fibers, and fascicular cambium become meristematic axial parenchyma). and form strips of vascular cambium. It is Based on the arrangement of the called interfascicular cambium. fusiform initials, two types of vascular This interfascicular cambium joins cambium are recognized. with the intrafascicular cambium on both Storied (Stratified cambium) and sides to form a continuous ring. It is called Non-Storied (Non-stratified cambium) a vascular cambial ring. The differences between interfascicular and intrafascicular cambia are summarised below: Ray initials

Intrafascicular Interfascicular Fusiform initials cambium cambium

Present inside the Present in between a vascular bundles the vascular bundles. Ray initials Originates from Originates from the procambium. the medullary rays. Fusiform initials Initially it forms a From the

part of the primary beginning it b meristem. forms a part of Figure 10.2: Tangential longitudinal the secondary section (TLS) of cambium (a) Storied meristem. cambium (b) Non-storied cambium Organization of Vascular Cambium If the fusiform initials are arranged in

39 horizontal tiers, with the end of the cells phloem and inward secondary xylem. of one tier appearing at approximately At places, cambium forms some the same level, as seen in tangential narrow horizontal bands of parenchyma longitudinal section (TLS), it is which passes through secondary phloem called storied (stratified) cambium. and xylem. These are the rays. It is the characteristic of the plants with Due to the continued formation of short fusiform initials. Whereas in plants secondary xylem and phloem through with long fusiform initials, they strongly vascular cambial activity, both the primary overlap at the ends, and this type of xylem and phloem get gradually crushed. cambium is called non-storied (non- . startified) cambium Secondary Xylem Ray Initials The secondary xylem, also called wood, is These are horizontally elongated cells. formed by a relatively complex meristem, They give rise to the ray cells and form the the vascular cambium, consisting of elements of the radial system of secondary vertically (axial) elongated fusiform initials xylem and phloem. and horizontally (radially) elongated ray initials. Activity of Vascular Cambium The vascular cambial ring, when active, cuts off new cells both towards the Xylotomy inner and outer side. The cells which The study of wood are produced outward form secondary by preparing sections for microscopic a A Portion of cambium observation.

Cambium b First formed xylem The axial system consists of vertical files

Cambium of treachery elements, fibers, and wood c Second formed xylem parenchyma. Whereas the radial system First formed xylem consists of rows of parenchymatous cells

Cambium oriented at right angles to the longitudinal Third formed xylem axis of xylem elements. d Second formed xylem First formed xylem The secondary xylem varies very greatly from species to species with reference to First formed phloem Cambium relative distribution of the different cell e Third formed xylem Second formed xylem types, density and other properties. It is First formed xylem of two types. First formed phloem Second formed phloem Porous Wood or Hard Wood Cambium Fourth formed xylem f Third formed xylem Generally, the dicotyledonous wood, Second formed xylem which has vessels is called porous wood First formed xylem or hard wood. Example: Morus rubra. Figure 10.3: Diagrammatic representa- tion of vascular cambial activity (a–f) Non- Porous Wood or Soft Wood

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Annual Rings Sometimes annual rings are called growth The activity of vascular cambium is rings but it should be remembered all the under the control of many physiological growth rings are not annual. In some trees and environmental factors. In temperate more than one growth ring is formed with regions, the climatic conditions are not in a year due to climatic changes. uniform throughout the year. In the Additional growth rings are spring season, cambium is very active developed within a year due to adverse and produces a large number of xylary natural calamities like drought, frost, elements having vessels/tracheids with defoliation, flood, mechanical injury wide lumen. The wood formed during and biotic factors during the middle this season is called spring wood or early of a growing season,which results in wood. The tracheary elements are fairly the formation of more than one annual thin walled. In winter, the cambium is less ring. Such rings are called pseudo- or active and forms fewer xylary elements false- annual rings. that have narrow vessels/ tracheids and Each annual ring corresponds to one this wood is called autumn wood or late year’s growth and on the basis of these wood.The treachery elements are with rings, the age of a particular plant can narrow lumen, very thick walled. easily be calculated. The determination of the age of a by counting the annual • Usually more rings is called dendrochronology. distinct annual rings are formed in the regions where Importance of Studying Growth Rings climatic variations are sharp. • Age of wood can be calculated. • Usually more distinct annual rings • The quality of timber can be are formed in temperate plants ascertained. and not in tropical plants. • Radio-Carbon dating can be • Usually least distinct annual rings verified. are formed in seashore region • Past climate and archaeological because the climatic conditions dating can be made. remain same throughout the year. • Generally annual rings are also • Provides evidence in forensic less distinct in desert plants. investigation.

The spring wood is lighter in colour and Dendroclimatology has a lower density whereas the autumn It is a branch of dendrochronology wood is darker and has a higher density. concerned with constructing records The annual ring denotes the of past climates and climatic events by combination of early wood and late wood analysis of tree growth characteristics, and the ring becomes evident to our eye especially growth rings. due to the high density of late wood.

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Fossil resins-Amber Plants secrete resins for their protective benefits.Amber is a fossilized tree resin especially from the wood, which has been appreciated c. Microscopic slide for its colour and natural A slide of 60-years-old holotype specimen of beauty since neolithic times. a flatworm ( ) permanently Lethacotyle fijiensis d. Ant inside Much valued from antiquity mounted in canada balsam. to the present as a gemstone, blastic amber amber is made into a variety of decorative objects. Amber is used in jewellery. It has also been used as a agent in folk .

Figure 10.12: Economic importance of wood (a–d) Secondary Phloem iii. Sun hemp-Crotalaria juncea The vascular cambial ring produces iv. Jute-Corchorus capsularis secondary phloem or bast on the outer side of the vascular bundle. Be friendly with your environment Just as the secondary xylem, the (Eco friendly) secondary phloem also has two tissue Why should not we use the natural systems – the axial (vertical) and the products which are made by plant radial (horizontal) systems derived fibres like , fancy bags, mobile respectively from the vertically elongated pouch, mat and gunny bags etc., fusiform initials and horizontally instead of using plastics or nylon? elongated ray initials of vascular cambium. While sieve elements, phloem fibre, and phloem parenchyma represent Periderm the axial system, phloem rays represent Whenever stems and roots increase the radial system. Life span of secondary in thickness by secondary growth, the phloem is less compared to secondary periderm, a protective tissue of secondary xylem. Secondary phloem is a living origin replaces the epidermis and often tissue that transports soluble organic primary cortex. The periderm consists of compounds made during photosynthesis phellem, phellogen, and phelloderm. to various parts of plant. Some commercially important phloem Phellem (Cork) or bast fibres are obtained from the It is the protective tissue composed of following plants. non-living cells with suberized walls and formed centrifugally (outward) by the i. Flax- ustitaissimum phellogen (cork cambium) as part of the ii. Hemp-Cannabis sativa periderm. It replaces the epidermis in

48 older stems and roots of many seed plants. Differences Between Phellem and It is characterized by regularly arranged Phelloderm tiers and rows of cells. It is broken here Phellem (Cork) Phelloderm and there by the presence of . (Secondary cortex) Cuticle Epidermis It is formed on It is formed on First cork cell the outer side of the inner side of Phellogen (Cork cambium) phellogen. phellogen. Cortex Cells are Cells are loosely a Cuticle compactly arranged with Epidermis arranged in intercellular Phellem(Cork) Phellogen regular tires and spaces. (Cork cambium) rows without Phelloderm (Secondary cortex) intercellular Cortex b spaces. Protective in As it contains Figure 10.13: The cross section of function. chloroplast, it periderm (a–b) synthesises and stores food. Phelloids Consists of non- Consists of Phellem (Cork) like cells which lack living cells with living cells, suberin in their walls. suberized walls. parenchymatous in nature and does not have suberin. Phellogen (Cork Cambium) Lenticels are Lenticels are It is a secondary lateral meristem. It present. absent. comprises homogenous meristematic cells unlike vascular cambium. It arises from epidermis, cortex, phloem or pericycle Rhytidome is a technical term used (extrastelar in origin). Its cells divide for the outer dead periclinally and produce radially arranged bark which consists of files of cells. The cells towards the outer periderm and isolated side differentiate into phellem (cork) and cortical or phloem tissues formed those towards the inside as phelloderm during successive secondary growth. (secondary cortex). Example: Quercus. Polyderm is found in the roots Phelloderm (Secondary cortex) and underground stems.eg. Rosaceae. It is a tissue resembling cortical living It refers to a special type of protective parenchyma produced centripetally tissues consisting of uniseriate (inward) from the phellogen as a part of the suberized layer alternating with periderm of stems and roots in seed plants. multiseriatenonsuberized cells in periderm.

49 Differences Between Vascular barks normally do not peeled off , scale barks Cambium and Cork Cambium peeled off . Vascular cambium Cork cambium Also called Also called cambium phellogen It arises from It arises from procambium and epidermis, cortex, interfascicular phloem, or parenchyma in pericyle in both stems and from stems and roots conjunctive parenchyma in roots Figure 10.14: Quercus Tree-showing It comprises long It comprises of ring bark fusiform and homogenous cells. short ray initials. It produces It produces secondary phloem phellem(cork) towards the outer towards outer side side and secondary and phelloderm xylem towards (secondary cortex) inner side. towards inner side.

Bark Figure 10.15: Guava tree showing scale Th e term ‘bark’ is commonly applied to all bark the tissues outside the vascular cambium of stem (i.e., periderm, cortex, primary ). Bark phloem and secondary phloem Lenticel is raised opening or pore on the protects the plant from parasitic fungi and epidermis or bark of stems and roots. insects, prevents water loss by evaporation It is formed during secondary growth and guards against variations of external in stems. When phellogen is more active temperature. It is an insect repellent, decay in the region of lenticels, a mass of loosely proof, fi reproof and is used in obtaining arranged thin-walled parenchyma cells drugs or spices. Th e phloem cells of the bark are formed. It is called are involved in conduction of food while complementary or . secondary cortical cells involved in storage. tissue filling tissue Lenticel is helpful in exchange of If the phellogen forms a complete cylinder gases and transpiration called lenticular around the stem, it gives rise to ring barks. transpiration. Example: Quercus. When the bark is formed in overlapping scale like layers, it is known as scale bark. Example: Guava. While ring

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10.2 Secondary Growth in Dicot root combination of conjunctive tissue located Secondary growth in dicot roots is essential just below the phloem bundles, and as a to provide strength to the growing aerial portion of pericycle tissue present above parts of the plants. It is similar to that of the the protoxylem to form a complete and secondary growth in dicot stem. However, continuous wavy ring. This wavy ring later there is marked difference in the manner of becomes circular and produces secondary the formation of vascular cambium. xylem and secondary phloem similar to the secondary growth in stems. The vascular cambium is completely secondary in origin. It originates from a

Epidermis Endodermis Pericycle

Primary phloem

Cambium

Primary xylem

ab Epidermis Cortex Endodermis Pericycle Primary phloem Secondary phloem Cambial ring Primary xylem Secondary xylem

cd

Epidermis Phellogen (Cork cambium) Pericycle Primary phloem Secondary phloem Phloem ray Cambial ring Primary xylem e Secondary xylem Xylem ray

Figure 10.17: Different stages of the secondary growth (diagrammatic) in a typical dicot root (a–e)

52 Differences Between Secondary Growth in Dicot Stem and Root Secondary growth in dicot stem Secondary growth in dicot root The cambial ring formed is circular in The cambial ring formed is wavy in the cross section from the beginning. beginning and later becomes circular. The cambial ring is partially primary The cambial ring is completely secondary (fascicular cambium)and partially in origin. secondary (Interfascicular cambium) in origin. Generally, periderm originates from the Generally, periderm originates from the cortical cells (extrastelar in origin). pericyle. (intrastealar in origin) More amount of cork is produced as stem Generally, less amount of cork is produced is aboveground as root is underground. Lenticels of periderm are prominent. Lenticels of periderm are not very prominent.

Pre-structure of Primary Structure Secondary Structure Primary Structure secondary growth Procambium Fascicular Axial Phloem cambium Fusiform initials Vascular Axial Xylem cambium Phloem rays DICOT STEM Medullary rays Inter fascicular cambium Ray initials Xylem rays Epidermis Cortex Cork cambium Phellem (cork) Phloem (Phellogen) Phelloderm (Secondary cortex)

Lenticels

Axial Phloem Fusiform initials Vascular Conjunctive Axial Xylem cambium tissue Ray initials Phloem rays DICOT ROOT Xylem rays

Pericycle Cork cambium Phellem (cork) (Phellogen) Phelloderm (Secondary cortex)

Tissue Lineages During Secondary Growth in Dicot Stem and Root

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rib sawing is the most common method fans, ensuring the removal of moisture in making timber. Timber is mainly uniformly, rapidly and completely. used for carpentry and building houses. In order to enrich the quality of timber, seasoning of wood is done. Timber is the most important tissue that sequestrates atmospheric carbon and this reduces global warming.

10.4.1 Seasoning of wood It is the process in which moisture content from the wood is removed. There are two types of seasoning. Figure 10.29: Kiln Seasoning 1. Air Seasoning is the process in which the moisture can be removed Activity without resorting to artificial heat. In this List out the uses of saw dust, shavings method of artificial seasoning, the cut and wood flour. timber pieces are left exposed in the open air and the moisture is removed naturally and gradually by the heat of the sun. It 10.4.2 Grain, Texture, and Figure of increases the strength, the combustibility Wood and renders the wood less subject to decay. Grain refers to the structural arrangement of wood, while texture shows the relative size and quality of the various types of wood. Figure of wood refers to the pattern formed by grains in wood when the wood is cut in the longitudinal direction. It depends on the grain and texture and their exposure by direction of sawing.

Ply wood Figure 10.28: Air Seasoning It is manufactured by 2. Kiln Seasoning is the process in gluing together 3 to 9 which the moisture can be removed thin layers or piles of by artificial method in an enclosed wood veneers. It is used in flooring, condition. The timber pieces are enclosed walls, false roof and vehicle interiors. in a steam-heater chamber into which air is introduced and circulated by

57 fusiform and ray initials. Fusiform initials give rise to the axial tissue system whereas ray initials give rise to radial tissue system of stems and roots. Wood is a very important product of secondary growth. It represents secondary xylem. It is classified in various ways. Based respectively on the presence or absence of vessels, wood is classified a. into two types. i.e., porous and non- porous wood. Based on the wood formed during seasons, it is classified into spring wood and autumn wood. The spring and autumn wood, together is called annual ring. The wood is also classified into wood (pale in colour) and wood (dark in colour). The lumen of the xylem vessels of heart wood are blocked by many b. balloon like ingrowths from neighbouring parenchymatous cells called . Figure 10.30: Shows grain, texure and tyloses figure of wood (a–b). The periderm, a secondary protective tissue consists of phellem, phellogen and phelloderm. Secondary growth produces a corky bark around the tree trunk that Activity protects the interior parts from heat, cold, etc. Secondary growth of root Collect some pieces of plywood, is different from stem in the method of analyse the layers and discuss yourself formation of vascular cambium. how it is made. Anomalous secondary growth is now referred as cambial variants. They are abnormal types of secondary growth Summary that occur in some dicots and monocots. Secondary growth deals with the formation Timber is derived from wood logs. In of additional vascular tissue by the order to enrich the quality of timber, activities of vascular and cork cambia and seasoning of wood is done through air secondary thickening meristem (STM). and kiln drying. Wood is characterized by It increases the girth of stem and roots colour, grain, texture and figure. of gymnosperms, most angiosperms, and some monocot plants. Vascular cambium possesses two kinds of initials they are,

58 Evaluation b. A. Complementary tissue, B. Phellem, C. Phellogen, 1. Consider the following D. Phelloderm. statements c. A. Phellogen, B. Phellem, In spring season C. Phelloderm, D. complementary vascular cambium tissue i. is less active d. A. Phelloderm, B. Phellem, ii. produces a large number of xylary C. Complementary tissue, elements D. Phellogen iii. forms vessels with wide cavities of 4. Inner, darker & harder portion of these, secondary xylem that cannot conduct a. (i) is correct but (ii) and (iii) are not water in an older dicot stem is called correct a. Alburnum b. Bast b. (i) is not correct but (ii) and (iii) are c. Wood d. Duramen correct 5. The common bottle cork is a product of c. (i) and (ii) are correct but (iii) is not a. Dermatogen correct b. Phellogen d. (i) and (ii) are not correct but (iii) is correct. c. Xylem 2. Usually, the do not d. Vascular cambium increase their girth, because 6. What is the fate of primary xylem in a a. They possess actively dividing dicot root showing extensive secondary cambium growth? b. They do not possess actively a. It is retained in the center of the axis dividing cambium b. It gets crushed c. Ceases activity of cambium c. May or may not get crushed d. All are correct d. It gets surrounded by primary 3. In the diagram of lenticel identify the phloem parts marked as A,B,C,D Assertion and Reason 7. These questions consist of two B statements each printed as Assertion and Reason. While answering

A these questions you are required to choose any one of the following four D responses.

C A. If both Assertion and Reason are true but the Reason is a correct a. A. phellem, B. Complementary explanation of the Assertion. tissue, C. Phelloderm, D. Phellogen.

59 B. If both Assertion and Reason are 15. A timber merchant bought 2 logs of true but Reason is not a correct wood from a forest & named them explanation of the Assertion A & B, The log A was 50 year old & B C. If Assertion is true but the Reason is was 20 years old. Which log of wood false. will last longer for the merchant? D. If both Assertion and Reason are Why? false. 16. A cross section of tree trunk contains 60 lighter and 60 darker rings. 1. Assertion: In woody stems the amount of heart wood continue to Determine the age of the tree and increase year after Year justify 17. A transverse section of the trunk of Reason: The activity of cambial ring continues uninterrupted a tree shows concentric rings which are known as growth rings. How are a. A b. B these rings formed? What are the c. C d. D significance of these rings? 2. Assertion: Secondary growth in 18. There are many tissues produced dicot roots occurs with the help of outside the vascular cambium in the vascular cambium and phellogen. stem. Explain them Reason: Vascular cambium is 19. When you go to a timber mart to completely primary in origin. collect timber for your construction a. A b. B of a new house, how will you select c. C d. D good timber? 20. Explain artificial seasoning. Answer the Following 8. When the plants shed their leaves how do they respire? 9. What is wood botanically? 10. In a forest, if the bark of a tree is damaged by the horn of a deer, How will the plant overcome the damage? 11. Differentiate the wood formed in Pinus from that of Morus 12. In which season the vessels of angiosperms are larger in size, why? 13. Central part of the wood is always dark. Why? 14. Continuous state of dividing tissue is called meristem. In connection to this, what is the role of lateral meristem?

60 ICT Corner

Characteristics of Dicot and Monocot Stem and Root

Let’s explore inside Stem and Root

Steps

• Scan the QR code or go to Google play store. • Type online labs and install it. • Select biology and select Characteristics of dicot and monocot stem and root. • Click free sign up and provide your basic information with valid mail-Id. • Login with your registered mail id and password. • Choose theory tab to know the basic about anatomical structure of plant parts. • Choose animation to view the sectioning process. • Choose simulation tab and view the section of plant parts under microscope. Activity • Do the section through simulation and record your observations.

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61 Unit V: Plant (Functional Organisation) Chapter 11 Transport in Plants

Learning Objectives The learner will be able to, Over 450 million years ago (the Ordovician • Recall knowledge of basic physical period in Paleozoic era) plants migrated and biological processes studied in from their own sophisticated water world previous classes. to newly formed land. The land had harsh environment; water availability was deeper • Classify, differentiate and compare and so plants struggled for getting water for the process of active and passive their very existence. Some of them failed transport. to survive and rest adopted themselves to • Understand the mechanism of the new world. The biggest adaptations absorption of water. followed for their survival was building • Analyse the various theories in their own water absorbing systems to ascent of sap. draw water from deep inside the land. The • Understand the process of creation and updating of water absorbing transpiration and Compare the system (vascular tissues) led to the diversity various types of transpiration. of the plant . The gregarious • Discuss the mechanism of phloem growth of prehistoric pteridophytes, translocation. gymnosperms and present-day flowering plants led to the biggest challenge in the • Understand the process behind transport of water from root to several mineral absorption. meters high trees against gravity. In this chapter, we will study the events taking Chapter Outline place between the gain of water in roots and loss in leaves and the mechanisms Types of transport 11.1 behind the basic physical and biological Cell to Cell transport 11.2 processes in the movement of water, gases 11.3 Plant water relations and minerals in plants. Further, we study 11.4 Absorption of water how food material synthesized in the leaf 11.5 Ascent of Sap can be transported to various utilizing and storage areas against struggles and 11.6 Transpiration challenges. 11.7 Translocation of organic solutes 11.8 Mineral absorption

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ii. Active transport: It is a biological process and it runs based on the Diffusion: The net movement of energy obtained from respiration. It molecules from a region of their is an uphill process. higher concentration to a region of their lower concentration along a concentration gradient until an 11.2 Cell to Cell Transport equilibrium is attained. Cell to cell or short distance transport covers the limited area and consists of few cells. They are the facilitators or tributaries Characteristics of diffusion to the long-distance transport. The i. It is a passive process, hence no energy driving force for the cell to cell transport expenditure involved. can be passive or active (Figure 11.1). The ii. It is independent of the living system. following chart illustrate the various types iii. Diffusion is obvious in gases and of cell to cell transport: liquids.

Cell to cell transport

Passive Transport Active Transport

Diffusion Facilitated Diffusion Channel Carrier Protein Channel Protein Carrier Protein Pumps

Figure 11.1: Cell to cell transport A 11.2.1 Passive Transport 1. Diffusion When we expose a lightened incense stick or mosquito coil or open a perfume bottle in a closed room, we can smell the odour HIGH CONCENTRATION LOW CONCENTRATION Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad everywhere in the room. This is due to the minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure dolor in hendreritB in even distribution of perfume molecules vulputate velit esse molestie consequat, vel illum dolore eu feugiat nulla facilisis at vero eros et accumsan et iusto odio dignissim qui blandit praesent luptatum zzril delenit augue duis dolore te feugait nulla facilisi. throughout the room. This process is Lorem ipsum dolor sit amet, cons ectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad called . minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut diffusion aliquip ex ea commodo consequat. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh In diffusion, the movement of euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad molecules is continuous and random in Figure 11.2: Distribution of molecules in order in all directions (Figure 11.2). diffusion (A) Initial stage (B) Final stage

64 iv. Diffusion is rapid over a shorter i. Size of molecule: Smaller molecules distance but extremely slow over a diffuse faster. longer distance. ii. Solubility of the molecule: v. The rate of diffusion is determined by soluble substances easily and rapidly temperature, concentration gradient pass through the membrane. But water and relative density. soluble substances are difficult to pass through the membrane. They must be Significance of diffusion in Plants facilitated to pass the membrane.

i. Gaseous exchange of O2 and CO2 between the atmosphere and stomata Types of Membrane Permeability of leaves takes place by the process A is made up of solute of diffusion. O2 is absorbed during particles dissolved in a solvent and the respiration and CO2 is absorbed during permeability of the above components photosynthesis. depends on the nature of cell ii. In transpiration, water vapour from membranes, which is given below: intercellular spaces diffuses into Impermeable: Inhibit the movement atmosphere through stomata by the of both solvent and solute molecules. process of diffusion. Example: Suberised, cutinesed or iii. The transport of ions in mineral salts liginifid cell walls. during passive absorption also takes They allow diffusion place by this process. Permeable: of both solvent and solute molecules through them. Example: Cellulosic cell Diffusion for wall. sterilization in Semi permeable surgical theatres Semi permeable: allow diffusion of solvent molecules Surgical theatres must but do not allow the passage of solute be free from germs to prevent infection molecule. Example: Parchment paper. during surgeries. A mixture of All bio Formalin and Potassium permanganate Selectively permeable: membranes allow some solutes to pass produces enormous fumes which will in addition to the solvent molecules. kill all pathogens in an enclosed area. Example: Plasmalemma, tonoplast, and This method is known as fumigation membranes of cell . and operates by diffusion.

In facilitated diffusion, molecules cross 2. Facilitated Diffusion the with the help of special Cell membranes allow water and nonpolar membrane called transport molecules to permeate by simple diffusion. proteins, without the expenditure of ATP. For transporting polar molecules such as There are two types of transport ions, , amino acids, nucleotides and proteins present in the cell membrane. many cell metabolites is not merely based They are channel protein and a carrier on concentration gradient. It depends on, protein.

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of ions or molecules. The pump action is OUTSIDEOUTSIDE an example of active transport. Example: Na+-K+-ATPase pump (Table 11.1).

MEMBRANE INSIDEINSIDE Table 11.1 Comparison of different transport mechanisms UNIPORT SYMPORT ANTIPORT Passive transport Direction of transport Active Figure 11.5: Property Simple Facilitated transport transports two types of molecules diffusion diffusion across the membrane in the same Nature of Physical Biological Biological direction. process iii. Antiport or Counter Transport: An Requirement is an integral membrane for presence antiport No Yes Yes transport protein that simultaneously of membrane transports two different molecules, protein Selectivity of in opposite directions, across the No Yes Yes membrane. molecule Saturation of No Yes Yes 11.2.2 Active Transport transport Uphill The main disadvantage of passive transport No No Yes processes like diffusion is the lack of control transport over the transport of selective molecules. Energy There is a possibility of harmful substances requirement No No Yes entering the cell by a concentration gradient (ATP) Sensitivity to in the diffusion process. But selective No Yes Yes permeability of cell membrane has a great inhibitors control over entry and exit of molecules. Active transport is the entry of molecules Check your grasp! against a concentration gradient and an What are the similarities and uphill process and it needs energy which differences between co- transport and comes from ATP. Passive transport uses counter transport? kinetic energy of molecules moving down Solution: a gradient whereas, active transport uses Similarity: In both system two molecules cellular energy to move them against a are involved for the unidirectional gradient. The transport proteins discussed in transport. facilitated diffusion can also transport ions or molecules against a concentration gradient Difference: In co-transport, two with the expenditure of cellular energy as molecules are transported together an active process. Pumps use a source of whereas, in counter transport two free energy such as ATP or light to drive molecules are transported in opposite the thermodynamically uphill transport direction to each other.

67 11.3 Plant Water Relations Significance of imbibition Water plays an essential role in the life i. During of seeds, imbibition of the plant. The availability of water increases the volume of seed enormously and leads to bursting of the seed coat. influences the external and internal structures of plants as protoplasm is made ii. It helps in the absorption of water by roots at the initial level. of 60-80% water. Water is a universal solvent since most of the substances get dissolved in it and the high tensile Activity strength of water molecule is helpful in the ascent of sap. Water maintains the Imbibition experiment internal temperature of the plant as well Collect 5 gm of gum from Drumstick as the turgidity of the cell. tree or Babool tree or Almond tree. Immerse in 100ml of water. After 24 hours observe the changes and discuss 11.3.1 Imbibition the results with your teacher. Colloidal systems such as gum, starch, proteins, cellulose, agar, gelatin when placed in water, will absorb a large volume of water and swell up. These substances are called imbibants and the phenomenon is imbibition.

Examples: 1. The swelling of dry seeds 2.The swelling of wooden windows, tables, doors due to high humidity during the rainy season.

The Power of 11.3.2 Water Potential (Ψ) Imbibition The concept of water potential was In olden days, small introduced in 1960 by Slatyer and Taylor. wooden pegs were Water potential is potential energy of inserted into crevices of rocks water in a system compared to pure water followed by continuous hydration. when both temperature and pressure are Due to imbibition the volume of kept the same. It is also a measure of how wooden peg increases and cuts off freely water molecules rocks precisely. can move in a particular environment or system. The gluten from wheat can take as Water potential is denoted much as 300% of its own weight by the Greek symbol Ψ

68 (psi) and measured in Pascal (Pa). At withdrawal of water from the cell decreases standard temperature, the water potential the water potential and the cell becomes of pure water is zero. Addition of solute flaccid. to pure water decreases the kinetic energy thereby decreasing the water potential. 3. Matric Potential (ΨM) Comparatively a solution always has Matric potential represents the attraction low water potential than pure water. between water and the hydrating colloid In a group of cells with different water or gel-like organic molecules in the cell potential, a water potential gradient is wall which is collectively termed as matric generated. Water will move from higher potential. Matric potential is also known water potential to lower water potential. as imbibition pressure. The matric potential is maximum (most negative Water potential (Ψ) can be determined by, value) in a dry material. : The 1. Solute concentration or Solute Example swelling of soaked seeds in water. potential ( ) ΨS 2. Pressure potential ( ) ΨP 11.3.3 Osmotic Pressure and Osmotic By correlating two factors, water potential Potential is written as, When a solution and its solvent (pure water) are separated by a semipermeable Ψ = Ψ + Ψ W S P membrane, a pressure is developed in the Water Potential = Solute potential + solution, due to the presence of dissolved Pressure potential solutes. This is called osmotic pressure (OP). Osmotic pressure is increased 1. Solute Potential (ΨS) with the increase of dissolved solutes in Solute potential, otherwise known as the solution. More concentrated solution osmotic potential denotes the effect of (low Ψ or Hypertonic) has high osmotic dissolved solute on water potential. In pure pressure. Similarly, less concentrated water, the addition of solute reduces its solution (high Ψ or Hypotonic) has low free energy and lowers the water potential osmotic pressure. The osmotic pressure value from zero to negative. Thus the value of pure water is always zero and it of solute potential is always negative. In a increases with the increase of solute solution at standard atmospheric pressure, concentration. Thus osmotic pressure water potential is always equal to solute always has a positive value and it is potential ( ). ΨW= ΨS represented as π.

2. Pressure Potential (ΨP) Osmotic potential is defined as Pressure potential is a mechanical force the ratio between the number of solute working against the effect of solute particles and the number of solvent potential. Increased pressure potential particles in a solution. Osmotic potential will increase water potential and water and osmotic pressure are numerically enters cell and cells become turgid. This equal. Osmotic potential has a negative positive hydrostatic pressure within the value whereas on the other hand osmotic cell is called . Likewise, pressure has a positive value.

69 11.3.4 Turgor Pressure and Wall It is equal to the difference of osmotic Pressure pressure and turgor pressure of a cell. The following three situations are seen in When a is placed in pure water plants: (hypotonic solution) the diffusion of water into the cell takes place by endosmosis. It • DPD in normal cell: DPD = OP – TP. creates a positive hydrostatic pressure on • DPD in fully turgid cell: Osmotic the rigid cell wall by the cell membrane. pressure is always equal to turgor Henceforth the pressure exerted by the cell pressure in a fully turgid cell. membrane towards the cell wall is Turgor • OP = TP or OP-TP =0. Hence DPD of Pressure (TP). fully turgid cell is zero. The cell wall reacts to this turgor • DPD in flaccid cell: If the cell is in pressure with equal and opposite force, flaccid condition there is no turgor and the counter-pressure exerted by the pressure or TP=0. Hence DPD = OP. cell wall towards cell membrane is wall pressure (WP). 11.3.6 Osmosis Turgor pressure and wall pressure Osmosis (Latin: Osmos-impulse, urge) is a make the cell fully turgid. special type of diffusion. It represents the TP + WP = Turgid. movement of water or solvent molecules through a selectively permeable Activity membrane from the place of its higher Find the role of turgor pressure in concentration (high water potential) to sudden closing of leaves when we the place of its lower concentration (low touch the ‘touch me not’ plant. water potential). Types of based on concentration 11.3.5 Diffusion Pressure Deficit (DPD) i. Hypertonic (Hyper = High; tonic = or Suction Pressure (SP) solute): This is a strong solution (low solvent/ high solute / low ) which Pure solvent (hypotonic) has higher Ψ from other solutions. diffusion pressure. Addition of solute in attracts solvent pure solvent lowers its diffusion pressure. ii. Hypotonic (Hypo = low; tonic = solute): The difference between the diffusion This is a weak solution (high solvent pressure of the solution and its solvent at /low or zero solute / high Ψ) and it a particular temperature and atmospheric diffuses water out to other solutions ( Figure 11.7). pressure is called as Diffusion Pressure termed by ). Deficit (DPD) Meyer (1938 ( = identical; = soute): DPD is increased by the addition of solute iii. Isotonic Iso tonic It refers to two solutions having same into a solvent system. Increased DPD concentration. In this condition the net favours endosmosis or it sucks the water movement of water molecule will be zero. from hypotonic solution; hence Renner The term hyper, hypo and isotonic are (1935) called it as Suction pressure. relative terms which can be used only

70 in comparison with another solution. Thistle funnel experiment 1. Types of osmosis Based on the direction of movement of water or solvent in an osmotic system, two types of osmosis can occur, they are Endosmosis and Exosmosis. i. Endosmosis: Endosmosis is defined as the osmotic entry of solvent into a cell or a system when it is placed in a pure water or hypotonic solution.

Figure 11.6: Thistle Funnel Experiment For example, dry raisins (high solute and low solvent) placed in the water, Mouth of a thistle funnel is tied with it swells up due to turgidity. goat bladder. It acts as a semipermeable membrane. Pour concentrated ii. Exosmosis: Exosmosis is defined as solution in the thistle funnel and the osmotic withdrawal of water from mark the level of solution. Place a cell or system when it is placed in a this in a beaker of water. After some hypertonic solution. Exosmosis in a time, water level in the funnel rises plant cell leads to plasmolysis. up steadily. This is due to the inward diffusion of water molecules through 2. Plasmolysis (Plasma = cytoplasm; the semipermeable membrane lysis = breakdown) (Figure 11.6). When a plant cell is kept in a hypertonic Conversely, if water in the beaker is solution, water leaves the cell due to replaced by a sugar solution and sugar exosmosis. As a result of water loss, solution in the thistle funnel replaced protoplasm shrinks and the cell membrane by water, what will be happen? is pulled away from the cell wall and finally, the cell becomes flaccid. This process is named as plasmolysis. Wilting of plants noticed under the condition of is an indication of plasmolysis. Three types of plasmolysis occur in plants: i) Incipient plasmolysis ii) Evident plasmolysis and iii) Final plasmolysis. Differences among them are given in table 11.2.

Significance Plasmolysis is exhibited only by living Figure 11.7: Types of solution based on cells and so it is used to test whether the concentration cell is living or dead.

71 3. Deplasmolysis 4. Reverse Osmosis The effect of plasmolysis can be reversed, Reverse Osmosis follows the same by transferring them back into water or principles of osmosis, but in the reverse hypotonic solution. Due to endosmosis, direction. In this process movement of the cell becomes turgid again. It regains its water is reversed by applying pressure to original shape and size. This phenomenon force the water against a concentration of the revival of the plasmolysed cell gradient of the solution. In regular is called deplasmolysis. Example: osmosis, the water molecules move from Immersion of dry raisin in water. the higher concentration (pure water = hypotonic) to lower concentration Osmoscope (salt water = hypertonic). But in reverse osmosis, the water molecules move from the lower concentration (salt water = hypertonic) to higher concentration (pure water = hypotonic) through a selectively permeable membrane (Figure 11.9).

Uses: Reverse osmosis is used for purification of drinking water and desalination of seawater.

Figure 11.8: Demonstration of Pressure Endosmosis by Potato Osmoscope Pure Water i. Take a peeled potato tuber and make a cavity inside with the help Salt Water of a knife. ii. Fill the cavity with concentrated Membrane sugar solution and mark the initial Movement of Water level. Reverse Osmosis iii. Place this setup in a beaker of pure Figure 11.9: water. iv. After 10 minutes observe the sugar solution level and record your Check your grasp! findings (Figure 11.8). If a cell in the cortex with DPD of 5atm v. With the help of your teacher is surrounded by hypodermal cells with discuss the results. DPD of 2atm, what will be direction of Instead of potato use beetroot or bottle- movement of water? guard and repeat the above experiment. Solution: Water will move from low Compare and discuss the results. DPD to high DPD (hypodermis 2 atm to cortex 5 atm).

72 Table 11.2: Difference between plasmolysis types. Incipient plasmolysis Evident plasmolysis Final plasmolysis No morphological Wilting of leaves appear. Severe wilting and symptoms appear in plants. drooping of leaves appear. The plasma membrane Plasma membrane completely Plasma membrane separates only at the corner detaches from the cell wall. completely detaches from from the cell wall of cells. cell wall with maximum shrinkage of volume. It is reversible. It is reversible. It is irreversible.

11.4 Absorption of Water Terrestrial plants have to absorb water from the soil to maintain turgidity, metabolic activities and growth. Absorption of water from soil takes place in two steps: 1. From soil to root hairs – either actively or passively. Figure 11.10: Structure of Root Hair 2. From root hairs further transport in the lateral direction to reach xylem, the 11.4.2 Path of Water Across Root Cells superhighway of water transport. Water is first absorbed by root hair and other epidermal cells through 11.4.1 Water Absorbing Organs imbibition from soil and moves radially Usually, absorption of water occurs in and centripetally across the cortex, plants through young roots. The zone endodermis, pericycle and finally reaches of rapid water absorption is root hairs. xylem elements osmotically. They are delicate structures which get There are three possible routes of continuously replaced by new ones. water (Figure 11.11). They are i) Root hairs are unicellular extensions of Apoplast ii) iii) . epidermal cells without cuticle. Root hairs Symplast Transmembrane route are extremely thin and numerous and they 1. Apoplast provide a large surface area for absorption The apoplast (Greek: apo = away; (Figure 11.10). plast = cell) consists of everything external

73 Figure 11.11: Path of water across root cells to the plasma membrane of the living 11.4.3 Mechanism of Water Absorption cell. The apoplast includes cell walls, (1949) recognized two distinct extra cellular spaces and the interior of Kramer mechanisms which independently operate dead cells such as vessel elements and in the absorption of water in plants. tracheids. In the apoplast pathway, water They are, i) active absorption ii) passive moves exclusively through the cell wall or the non-living part of the plant without absorption. crossing any membrane. The apoplast is a continuous system. 1. Active Absorption The mechanism of water absorption due to 2. Symplast forces generated in the root itself is called The (Greek: = within; = symplast sym plast active absorption. Active absorption may cell) consists of the entire mass of cytosol be osmotic or non-osmotic. of all the living cells in a plant, as well as the i. Osmotic active absorption plasmodesmata, the cytoplasmic channel that interconnects them. The theory of osmotic active absorption was postulated by In the symplastic route, water has to cross Atkins (1916) and (1923). According to plasma membrane to enter the cytoplasm Preistley this theory, the first step in the absorption of outer root cell; then it will move within is soil water imbibed by cell wall of the root adjoining cytoplasm through plasmodesmata hair followed by osmosis. The soil water around the vacuoles without the necessity to is hypotonic and cell sap is hypertonic. cross more membrane, till it reaches xylem. Therefore, soil water diffuses into root hair along the concentration gradient 3. Transmembrane route (endosmosis). When the root hair becomes In transmembrane pathway water fully turgid, it becomes hypotonic and sequentially enters a cell on one side and water moves osmotically to the outer most exits from the cell on the other side. In cortical cell. In the same way, water enters this pathway, water crosses at least two into inner cortex, endodermis, pericycle membranes for each cell. Transport across and finally reaches protoxylem. As the the tonoplast is also involved.

74 sap reaches the protoxylem a pressure is in the rate of respiration and also the rate developed known as root pressure. This of absorption of water. theory involves the symplastic movement of water. 2. Passive Absorption Objections to osmotic theory: 1.The In passive absorption, roots do not play cell sap concentration in xylem is not any role in the absorption of water and always high. 2. Root pressure is not is regulated by transpiration only. Due to universal in all plants especially in trees. transpiration, water is lost from leaf cells along with a drop in turgor pressure. It ii. Non-Osmotic active absorption increases DPD in leaf cells and leads to Bennet-Clark (1936), Thimann (1951) withdrawal of water from adjacent xylem and Kramer (1959) observed absorption of water even if the concentration of cell cells. In xylem, a tension is developed sap in the root hair is lower than that of and is transmitted downward up to root the soil water. Such a movement requires resulting in the absorption of water from an expenditure of energy released by the soil. respiration (ATP). Thus, there is a In passive absorption (Table 11.3), link between water absorption and the path of water may be symplastic or respiration. It is evident from the fact that apoplastic. It accounts for about 98% of when respiratory inhibitors like KCN, the total water uptake by plants. Chloroform are applied there is a decrease

Concept Map - Movement of water in an osmotic system based on various parameters

High Water Low Water Potential Potential Low / Zero solute High solute (Zero) (Negative value) concentration concentration

Low High High solvent DPD Low solvent Concentration DPD Concentration

Low Osmotic High Osmotic Hypertonic Hypotonic Pressure Pressure (Zero) (Positive value)

High osmotic Low osmotic potential potential (Zero) PURE SALT (Negative Value) WATER WATER

75 Table: 11.3 Differences between Active Absorption and Passive Absorption Active Passive absorption absorption Active absorption The pressure for takes place by the absorption is not activity of root and developed in roots root hairs and hence roots play passive role Transpiration has Absorption no effect on active regulated by absorption transpiration The root hairs The absorption have high DPD occurs due to as compared to tension created soil solution and in xylem sap by therefore water is transpiration pull, taken by tension thus water is sucked in by the tension Respiratory energy Respiratory energy needed not required It involves Both symplast Figure 11.12: Balsam plant and symplastic and apoplast dye experiment movement of water movement of water involved 11.5.1 The Path of Ascent of Sap 11.5 Ascent of Sap There is no doubt; water travels up along the vascular tissue. But vascular tissue has two In the last chapter, we studied about water components namely Xylem and Phloem. absorption from roots to xylem in a lateral Of these two, which is responsible for the direction and here we will learn about ascent of sap? The following experiment the mechanism of distribution of water will prove that xylem is the only element inside the plant. Like tributaries join through which water moves up. together to form a river, millions of root hairs conduct a small amount of water and Cut a branch of balsam plant and confluence in xylem, the superhighway of place it in a beaker containing eosin water conduction. Xylem handles a large (red colour dye) water. After some amount of water to conduct to many parts time, a red streak appears on the stem in an upward direction. indicating the ascent of water. Remove The water within the xylem along with the plant from water and cut a transverse section of the stem and observe it under dissolved minerals from roots is called sap and its upward transport is called ascent the microscope. Only xylem element is of sap. coloured red, which indicates the path

76 of water is xylem. Phloem is not colored into the inner cortex of the stem, the indicating that it has no role in the ascent galvanometer showed high electrical of sap (Figure 11.12). activity. Bose believed a rhythmic pulsating movement of inner cortex like a Mechanism of Ascent of Sap pump (similar to the beating of the heart) In ascent of sap, the biggest challenge is the is responsible for the ascent of sap. He force required to lift the water to the top concluded that cells associated with xylem of the tallest trees. A number of theories exhibit pumping action and pumps the have been put forward to explain the sap laterally into xylem cells. mechanism of the ascent of sap. They are, A. Vital force theories, B. Root pressure Objections to vital force theories theory, and C. Physical force theory. i. Strasburger (1889) and Overton (1911) experimentally proved that living 11.5.2 Vital Force Theories cells are not mandatory for the ascent of According to vital force theories, living cells sap. For this, he selected an old oak tree are mandatory for the ascent of sap. Based trunk which when immersed in picric on this the following two theories derived: acid and subjected to excessive heat killed 1. Relay pump theory of Godlewski all the living cells of the trunk. The trunk (1884) when dipped in water, the ascent of sap Periodic changes in osmotic pressure took place. of living cells of the xylem parenchyma ii. Pumping action of living cells should and medullary ray act as a pump for the be in between two xylem elements movement of water. (vertically) and not on lateral sides. 2. Pulsation theory of J.C.Bose (1923) 11.5.3 Root Pressure Theory Bose invented an instrument called If a plant which is watered well is cut a few Crescograph, which consists of an electric probe connected to a galvanometer inches above the ground level, sap exudes (Figure 11.13). When a probe is inserted out with some force. This is called sap exudation or bleeding. Stephen Hales, father of observed this phenomenon and coined the term ‘Root Pressure’. Stoking (1956) defined root pressure as “a pressure developing in the tracheary elements of the xylem as a result of metabolic activities of the root”. B u t t h e following objections have been raised against root pressure theory: i. Root pressure is totally absent in gymnosperms, which includes some of the tallest plants. ii. There is no relationship between Figure 11.13: J.C. Bose the ascent of sap and root pressure. For

77 example, in summer, the rate of the ascent 3. Cohesion-tension or Cohesion and of sap is more due to transpiration in spite transpiration pull theory of the fact that root pressure is very low. Cohesion-tension theory was originally On the other hand, in winter when the proposed by Dixon and Jolly (1894) and rate of ascent of sap is low, a high root again put forward by Dixon (1914, 1924). pressure is found. This theory is based on the following iii. Ascent of sap continues even in the features: absence of roots i. Strong cohesive force or tensile iv. The magnitude of root pressure strength of water is about 2atm, which can raise the water Water molecules have the strong level up to few feet only, whereas the tallest mutual force of attraction called cohesive trees are more than 100m high. force due to which they cannot be easily separated from one another. Further, the 11.5.4 Physical Force Theory attraction between a water molecule and Physical force theories suggest that ascent the wall of the xylem element is called of sap takes place through the dead xylem adhesion. These cohesive and adhesive vessel and the mechanism is entirely force works together to form an unbroken physical and living cells are not involved. continuous water in the xylem. The magnitude of the cohesive force is 1. theory much high (350 atm) and is more than Boehm (1809) suggested that the xylem enough to ascent sap in the tallest trees. vessels work like a capillary tube. This ii. Continuity of the water column in capillarity of the vessels under normal the plant atmospheric pressure is responsible for An important factor which can break the ascent of sap. This theory was rejected the water column is the introduction of because the magnitude of capillary force air bubbles in the xylem. Gas bubbles can raise water level only up to a certain expanding and displacing water within height. Further, the xylem vessels are the xylem element is called cavitation broader than the which actually or embolism. However, the overall conducts more water and against the continuity of the water column remains capillary theory. undisturbed since water diffuses into the 2. Imbibition theory adjacent xylem elements for continuing This theory was first proposed by Unger ascent of sap. (1876) and supported by Sachs (1878). iii. Transpiration pull or Tension in This theory illustrates, that water is the unbroken water column imbibed through the cell wall materials The unbroken water column from leaf and not by the lumen. This theory was to root is just like a rope. If the rope is rejected based on the ringing experiment, pulled from the top, the entire rope will which proved that water moves through move upward. In plants, such a pull is the lumen of the cell and not by a cell wall. generated by the process of transpiration which is known as transpiration pull.

78 79 Water vapour evaporates from mesophyll cells to the intercellular Activity spaces near stomata as a result of active Select a leafy twig of fully grown plant transpiration. The water vapours are then in your school campus. Cover the transpired through the stomatal pores. twig with a transparent polythene bag Loss of water from mesophyll cells causes a and tie the mouth of the bag at the decrease in water potential. So, water moves base of the twig. Observe the changes as a pull from cell to cell along the water after two hours and discuss with your potential gradient. This tension, generated teacher at the top (leaf) of the unbroken water column, is transmitted downwards from petiole, stem and finally reaches the roots. 11.6.1 Types of Transpiration The cohesion theory is the most accepted Transpiration is of following three types: among the plant physiologists today. 1. Stomatal transpiration Stomata are microscopic structures present 11.6 Transpiration in high number on the lower epidermis of Water absorbed by roots ultimately leaves. This is the most dominant form of reaches the leaf and gets released into transpiration and being responsible for the atmosphere in the form of vapour. most of the water loss (90 - 95%) in plants. Only a small fraction of water (less than 2. Lenticular transpiration 5%) is utilized in and In stems of woody plants and trees, the metabolic process. epidermis is replaced by periderm because The loss of excess of water in the form of secondary growth. In order to provide of vapour from various aerial parts of the gaseous exchange between the living cells plant is called transpiration. Transpiration and outer atmosphere, some pores which is a kind of evaporation but differs by the looks like lens-shaped raised spots are involvement of . The present on the surface of the stem called amount of water transpired is astounding Lenticels. The loss of water from lenticels (Table 11.4). The water may move through is very insignificant as it amounts to only the xylem at a rate as fast as 75cm /min. 0.1% of the total. 3. Cuticular transpiration The cuticle is a waxy or resinous layer Table: 11.4 Rate of Transpiration in of , a fatty substance covering the some plants cutin epidermis of leaves and other plant parts. Plant Transpiration per day Loss of water through cuticle is relatively Corn plant 2 Litres small and it is only about 5 to 10 % of the 5 Litres Sunflower total transpiration. The thickness of cuticle 200 Litres Maple tree increases in and transpiration Date palm 450 Litres is very much reduced or totally absent.

80 11.6.2 Structure of Stomata Different theories have been proposed The epidermis of leaves and green stems regarding opening and closing of stomata. The important theories of stomatal possess many small pores called stomata. The length and breadth of stomata is movement are as follows, about 10-40μ and 3-10μ respectively. 1. Theory of Photosynthesis in guard cells Mature leaves contain between 50 and 2. Starch – Sugar interconversion theory 2. 500 stomata per mm Stomata are made 3. Active potassium transport ion concept up of two guard cells, special semi-lunar or kidney-shaped living epidermal cells 1. Theory of Photosynthesis in guard in the epidermis. Guard cells are attached cells to surrounding epidermal cells known as Von Mohl (1856) observed that stomata open in light and close in the night. subsidiary cells or accessory cells. The guard cells are joined together at each According to him, chloroplasts present end but they are free to separate to form a in the guard cells photosynthesize in pore between them. The inner wall of the the presence of light resulting in the is thicker than the outer wall production of (Sugar) which (Figure 11.14). The stoma opens to the increases osmotic pressure in guard cells. It leads to the entry of water from other interior into a cavity called sub-stomatal cell and stomatal aperture opens. The cavity which remains connected with the intercellular spaces. above process vice versa in night leads to closure of stomata. Demerits 1. Chloroplast of guard cells is poorly developed and incapable of performing photosynthesis. 2. The guard cells already possess much amount of stored sugars. Guard cells 2. Starch – Sugar Interconversion theory i. According to Lloyd (1908), turgidity Figure 11.14: Structure of Stomata of guard cell depends on interconversion, of starch and sugar. It was supported by 11.6.3 Mechanism of Stomatal Movement Loftfield (1921) as he found guard cells Stomatal movements are regulated by the containing sugar during the daytime when change of turgor pressure in guard cells. they are open and starch during the night When water enters the guard cell, it swells when they are closed. and its unevenly thickened walls stretch ii. Sayre (1920) observed that the up resulting in the opening of stomata. opening and closing of stomata depends This is due to concave non-elastic nature upon change in pH of guard cells. of inner wall pulled away from each According to him stomata open at high other and stretching of the convex elastic pH during day time and become closed natured outer wall of guard cell. at low pH at night. Utilization of CO2

81 by photosynthesis during light period causes an increase in pH resulting in the conversion of starch to sugar. Sugar increase in cell favours endosmosis and increases the turgor pressure which leads to opening of stomata. Likewise, accumulation of CO2 in cells during night decrease the pH level resulting in the conversion of sugar to starch. Starch decreases the turgor pressure of guard cell and stomata close. iii. The discovery of in guard cells by phosphorylase Hanes Figure 11.15: Steward Scheme (1940) greatly supports the starch-sugar interconversion theory. The enzyme iii. It fails to explain the drastic change phosphorylase hydrolyses starch into sugar in pH from 5 to 7 by change of CO2. and high pH followed by endosmosis and 3. Theory of K+ transport the opening of stomata during light. The This theory was proposed by Levit takes place during the night. vice versa (1974) and elaborated by Raschke (1975). According to this theory, the following steps are involved in the stomatal opening:

iv. Steward (1964) proposed a slightly modified scheme of starch-sugar interconversion theory. According to him, Glucose-1-phosphate is osmotically inactive. Removal of phosphate from Glucose-1-phosphate converts to Glucose which is osmotically active and increases the concentration of guard cell leading to opening of stomata (Figure 11.15).

Objections to Starch-sugar Theory of K+ transport interconversion theory Figure 11.16: i. In monocots, guard cell does not Opening of stomata have starch. ii. There is no evidence to show the In light presence of sugar at a time when starch i. In guard cell, starch is converted disappears and stomata open. into organic acid (malic acid).

82 ii. Malic acid in guard cell dissociates i. In dark photosynthesis stops and to malate anion and proton (H+). respiration continues with accumulation

iii. Protons are transported through of CO2 in the sub-stomatal cavity. the membrane into nearby subsidiary cells ii. Accumulation of CO2 in cell lowers with the exchange of K+ (Potassium ions) the pH level. from subsidiary cells to guard cells. This iii. Low pH and a shortage of water in process involves an electrical gradient and the guard cell activate the stress hormone is called . ion exchange Abscisic acid (ABA). iv. This ion exchange is an active iv. ABA stops further entry of K+ ions process and consumes ATP for energy. and also induce K+ ions to leak out to v. Increased K+ ions in the guard subsidiary cells from guard cell. cell are balanced by Cl– ions. Increase in v. Loss of water from guard cell solute concentration decreases the water reduces turgor pressure and causes closure potential in the guard cell. of stomata (Figure 11.17). vi. Guard cell becomes hypertonic and favours the entry of water from 11.6.4 Factors Affecting Rate of surrounding cells. Transpiration vii. Increased turgor pressure due to The factors affecting the rate of the entry of water opens the stomatal pore transpiration can be categorized into (Figure 11.16). two groups. They are 1. External or Environmental factors and 2. Internal or In Dark plant factors. 1. External or Environmental factors i. Atmospheric humidity: The rate of transpiration is greatly reduced when the atmosphere is very humid. As the air becomes dry, the rate of transpiration is also increased proportionately. ii. Temperature: With the increase in atmospheric temperature, the rate of transpiration also increases. However, at very high-temperatures stomata closes because of flaccidity and transpiration stop. iii. Light: Light intensity increases the temperature. As in temperature, transpiration is increased in high light intensity and is decreased in low light intensity. Light + Figure 11.17: Theory of K transport also increases the permeability of the Closing of stomata cell membrane, making it easy for water molecules to move out of the cell.

83 iv. Wind velocity: In still air, the 2. Internal factors surface above the stomata get saturated i. Leaf area: If the leaf area is more, with water vapours and there is no need transpiration is faster and so xerophytes for more water vapour to come out. If reduce their leaf size. the wind is breezy, water vapour gets ii. Leaf structure: Some anatomical carried away near leaf surface and DPD is features of leaves like sunken stomata, the created to draw more vapour from the leaf presence of hairs, cuticle, the presence of cells enhancing transpiration. However, hydrophilic substances like gum, mucilage high wind velocity creates an extreme help to reduce the rate of transpiration. In increase in water loss and leads to a xerophytes the structural modifications reduced rate of transpiration and stomata are remarkable. To avoid transpiration, as remain closed. in Opuntia the stem is flattened to look like leaves called Phylloclade. Cladode or cladophyll in Asparagus is a modified Activity stem capable of limited growth looking What will happen if an indoor plant is like leaves. In some plants, the petioles placed under fan and AC? are flattened and widened, to become phyllodes example Acacia melanoxylon. 11.6.5 Plant Antitranspirants v. Atmospheric pressure: In low atmospheric pressure, the rate of The term antitranspirant is used to transpiration increases. Hills favour high designate any material applied to plants transpiration rate due to low atmospheric for the purpose of retarding transpiration. pressure. However, it is neutralized by low An ideal antitranspirant checks the temperature prevailing in the hills. transpiration process without disturbing the process of gaseous exchange. Plant vi. Water: Adequate amount of water in the soil is a pre-requisite for optimum plant antitranspirants are two types: growth. Excessive loss of water through 1. To act as a physical barrier above the transpiration leads to wilting. In general, stomata there are three types of wilting as follows, Colourless plastics, Silicone oil and low a. Incipient wilting: Water content of viscosity waxes are sprayed on leaves plant cell decreases but the symptoms are forming a thin film to act as a physical not visible. barrier (for transpiration) for water but permeable to CO and O . The success rate b. Temporary wilting: On hot summer 2 2 days, the freshness of herbaceous plants of a physical barrier is limited. reduces turgor pressure at the day time 2. Induction of Stomata closure and regains it at night. Carbon-di-oxide induces stomatal c. Permanent wilting: The absorption closure and acts as a natural of water virtually ceases because the plant antitranspirant. Further, the advantage cell does not get water from any source of using CO2 as an antitranspirant is its and the plant cell passes into a state of inhibition of photorespiration. Phenyl permanent wilting. Mercuric Acetate (PMA), when applied

84 as a foliar spray to plants, induces partial near vein endings (xylem and Phloem). stomatal closure for two weeks or more The liquid coming out of hydathode is without any toxic effect. Use of abscisic not pure water but a solution containing a acid highly induces the closing of stomata. number of dissolved substances. Dodecenyl succinic acid also effects on 11.6.7 Measurement of Transpiration stomatal closure. 1. Ganongs potometer Uses: Ganongs potometer is used to measure • Antitranspirants reduce the the rate of transpiration indirectly. In this, enormous loss of water by transpiration the amount of water absorbed is measured in crop plants. and assumed that this amount is equal to • Useful for seedling transplantations the amount of water transpired. in nurseries. Apparatus consists of a horizontal 11.6.6 Guttation graduated tube which is bent in opposite directions at the ends. One bent end is wide During high humidity in the atmosphere, and the other is narrow. A reservoir is fixed the rate of transpiration is much reduced. to the horizontal tube near the wider end. When plants absorb water in such a The reservoir has a stopcock to regulate condition root pressure is developed due water flow. The apparatus is filled with to excess water within the plant. Thus water from reservoir. A twig or a small plant excess water exudates as liquid from the is fixed to the wider arm through a split edges of the leaves and is called . guttation cock. The other bent end of the horizontal Example: Grasses, tomato, potato, brinjal tube is dipped into a beaker containing and Guttation occurs through Alocasia. coloured water. An air bubble is introduced stomata like pores called hydathodes into the graduated tube at the narrow end generally present in plants that grow in (Figure 11.19). keep this apparatus in bright moist and shady places. Pores are present sunlight and observe.As transpiration takes over a mass of loosely arranged cells with place, the air bubble will move towards large intercellular spaces called epithem the twig. The loss is compensated by water (Figure 11.18). This mass of tissue lies

Figure 11.18: Structure of Hydathode Figure 11.19: Ganongs Potometer

85 absorption through the xylem portion of utilization is known as translocation of the twig. Thus, the rate of water absorption organic solutes. The term solute denotes is equal to the rate of transpiration. food material that moves in a solution.

2. Cobalt chloride (CoCl2) paper method 11.7.1 Path of Translocation Select a healthy dorsiventral leaf and clean It has now been well established that its upper and lower surface with dry cotton. phloem is the path of translocation of Now place a dry Cobalt chloride ( ) CoCl2 strips on both surface and immediately cover solutes. Ringing or girdling experiment the paper with glass slides and immobilize will clearly demonstrate the translocation them. It will be observed after some time of solute by phloem. that the CoCl strip of lower epidermis turns 2 11.7.2 Ringing or girdling experiment pink. This indicates that CoCl2 becomes The experiment involves the removal of all hydrated (CoCl2.2H2O or CoCl2.4H2O) due to water vapours coming out through the tissue outside to vascular cambium (bark, stomata. The rate of transpiration is more on cortex, and phloem) in woody stems except the lower surface than in the upper surface xylem. Xylem is the only remaining tissue in of the dorsiventral leaf. the girdled area which connects upper and lower part of the plant. This setup is placed in a 11.6.8 Significance of transpiration beaker of water. After some time, it is observed Transpiration leads to loss of water, as that a swelling on the upper part of the ring stated earlier in this lesson 95% of absorbed appears as a result of the accumulation of food water is lost in transpiration. It seems to be material (Figure 11.20). If the experiment an evil process to plants. However, number continues within days, the roots die first. It of process like absorption of water, ascent is because, the supply of food material to the of sap and mineral absorption directly root is cut down by the removal of phloem. relay on the transpiration. Moreover plants The roots cannot synthesize their food and so withstand against scorching sunlight due they die first. As the roots gradually die the to transpiration. Hence the transpiration upper part (stem), which depends on root for is a “necessary evil” as stated by Curtis. the ascent of sap, will ultimately die. 11.7 Translocation of Organic Solutes Leaves synthesize food material through photosynthesis and store in the form of starch grains. When required the starch is converted into simple sugars. They must be transported to various parts of the plant system for RingRing off bark SwoSwollenl rremovede ved further utilization. However, the site of food ttissueissu Xylem production (leaves) and site of utilization are separated far apart. Hence, the organic food has to be transported to these areas. Water The phenomenon of food transportation from the site of synthesis to the site of Figure 11.20: Ringing experiment

86 11.7.3 Direction of Translocation Sink is defined as any in plants Phloem translocates the products of which receives food from source.Example: photosynthesis from leaves to the area Roots, tubers, developing fruits and of growth and storage, in the following immature leaves (Figure 11.21). directions, 11.7.5 Phloem Loading Downward direction: From leaves to stem and roots. The movement of photosynthates (products of photosynthesis) from : From leaves to Upward direction mesophyll cells to phloem sieve elements developing , , fruits for of mature leaves is known as consumption and storage. Germination phloem . It consists of three steps. of seeds is also a good example of upward loading translocation. : From cells of pith to Radial direction Why plants transport cortex and epidermis, the food materials sugars as sucrose are radially translocated. and not as starch or glucose or fructose? 11.7.4 Source and Sink Glucose and Fructose are simple is defined as any organ in plants Source monosaccharides, whereas, Sucrose which are capable of exporting food is a disaccharide composed of materials to the areas of or glucose and fructose. Starch is a to the areas of storage. Examples: Mature polysaccharide of glucose. Sucrose leaves, germinating seeds. and starch are more efficient in energy storage when compared to glucose and fructose, but starch is insoluble in water. So it cannot be transported via phloem and the next choice is sucrose, being water soluble and energy efficient, sucrose is chosen as the carrier of energy from leaves to different parts of the plant. Sucrose has low viscosity even at high concentrations and has no reducing ends which makes it inert than glucose or fructose.During photosynthesis, starch is synthesized and stored in the chloroplast stroma and sucrose is synthesized in the leaf cytosol from which it diffuses to the rest of the plant.

Figure 11.21: Source and Sink

87 i. Sieve tube conducts sucrose only. 2. Activated diffusion theory But the in chloroplast photosynthate This theory was first proposed by Mason mostly in the form of starch or and Maskell (1936). According to this trios-phosphate which has to be theory, the diffusion in sieve tube is transported to the cytoplasm where it accelerated either by activating the will be converted into sucrose for further diffusing molecules or by reducing the translocation. protoplasmic resistance to their diffusion. ii. Sucrose moves from mesophyll to nearby sieve elements by short distance 3. Electro-Osmotic theory transport. The theory of electro osmosis was proposed by Fenson (1957) and Spanner iii. From sieve tube to sink by (1958). According to this, an electric- long-distance transport. potential across the sieve plate causes the movement of water along with solutes. 11.7.6 Phloem Unloading This theory fails to explain several From sieve elements sucrose is translocated problems concerning translocation. into sink organs such as roots, tubers, flowers and fruits and this process is 4. Munch Mass Flow hypothesis Mass flow theory was first proposed by termed as phloem unloading. It consists of three steps: Munch (1930) and elaborated by Crafts (1938). According to this hypothesis, 1. Sieve element unloading: Sucrose organic substances or solutes move from leave from sieve elements. the region of high osmotic pressure (from : Movement 2. Short distance transport mesophyll) to the region of low osmotic of sucrose to sink cells. pressure along the turgor pressure 3. Storage and metabolism: The final step gradient. The principle involved in this when sugars are stored or metabolized hypothesis can be explained by a simple in sink cells. physical system as shown in figure 11.22. 11.7.7 Mechanism of Translocation Two chambers “A” and “B” made Several hypotheses have been proposed to up of semipermeable membranes are explain the mechanism of translocation. connected by tube “T” immersed in a Some of them are given below: reservoir of water. Chamber “A” contains highly concentrated sugar solution 1. Diffusion hypothesis while chamber “B” contains dilute sugar As in diffusion process, this theory states solution. The following changes were the translocation of food from higher observed in the system, concentration (from the place of synthesis) to lower concentration (to the place of i. The high concentration sugar utilization) by the simple physical process. solution of chamber “A” is in a hypertonic However, the theory was rejected because state which draws water from the reservoir the speed of translocation is much higher by endosmosis. than simple diffusion and translocation is ii. Due to the continuous entry of a biological process which any can water into chamber “A”, turgor pressure is halt. increased.

88 iii. Increase in turgor pressure in the phloem to the cells of stem and roots chamber “A” force, the mass flow of sugar along the gradient turgor pressure. solution to chamber “B” through the tube In the cells of stem and roots, the organic “T” along turgor pressure gradient. solutes are either consumed or converted iv. The movement of solute will continue into insoluble form and the excess water till the solution in both the chambers is released into xylem (by turgor pressure attains the state of isotonic condition and gradient) through cambium. the system becomes inactive. v. However, if new sugar solution is Merits: added in chamber “A”, the system will start i. When a woody or to run again. is girdled, the sap contains high sugar containing exudates from cut end. A similar analogous system as given in the experiment exists in plants: ii. Positive concentration gradient disappears when plants are defoliated. Chamber “A” is analogous to mesophyll cells of the leaves which contain a higher Objections: concentration of food material in soluble i. This hypothesis explains the form. In short “A” is the production point unidirectional movement of solute only. called “source”. However, bidirectional movement of Chamber “B” is analogous to cells of solute is commonly observed in plants. stem and roots where the food material is ii. Osmotic pressure of mesophyll utilized. In short “B” is consumption end cells and that of root hair do not confirm called “sink”. the requirements. Tube “T” is analogous to the sieve tube iii. This theory gives passive role to of phloem. sieve tube and protoplasm, while some Mesophyll cells draw water from the workers demonstrated the involvement xylem (reservoir of the experiment) of of ATP. the leaf by endosmosis leading to increase in the turgor pressure of mesophyll cell. 11.8 Mineral Absorption The turgor pressure in the cells of stem Minerals in soil exist in two forms, either and the roots are comparatively low and dissolved in soil solution or adsorbed by hence, the soluble organic solutes begin colloidal clay particle. Previously, it was to flow en masse from mesophyll through mistakenly assumed that absorption of mineral salts from soil took place along with absorption of water. But absorption of minerals and ascent of sap are identified as two independent processes. Minerals are absorbed not only by root hairs but also by the cells of epiblema. Plasma membrane of root cells are not Figure 11.22: A model demonstrating permeable to all ions and also all ions of the Mass flow hyphothesis same salt are not absorbed in equal rate.

89 Penetration and accumulation of ions into tightly but oscillate within a small volume living cells or tissues from surrounding of space called oscillation volume. Due to medium by crossing membrane is called small space, both ions overlap each other’s mineral absorption. Movement of ions oscillation volume and exchange takes into and out of cells or tissues is termed place (Figure 11.23). as transport or flux. Entry of the ion ii. Carbonic Acid Exchange Theory: into cell is called influx and exit is called According to this theory, soil solution efflux. Various theories have been put plays an important role by acting as forward to explain this mechanism. a medium for ion exchange. The CO2 They are categorized under passive released during respiration of root cells mechanisms (without the involvement of combines with water to form carbonic acid metabolic energy) and active mechanisms (H2CO3). Carbonic acid dissociates into + – (involvement of metabolic energy). H and HCO3 in the soil solution. These H+ ions exchange with cations adsorbed 11.8.1 Passive Absorption on clay particles and the cations from 1. Ion-Exchange: micelles get released into soil solution and Ions of external soil solution were gets adsorbed on root cells (Figure 11.24). exchanged with same charged (anion for anion or cation for cation) ions of the root cells. There are two theories explaining this process of ion exchange namely: i. Contact exchange and ii. Carbonic acid exchange. i. Contact Exchange Theory: According to this theory, the ions adsorbed on the surface of root cells and clay particles (or clay micelles) are not held Figure 11.24: Carbonic Acid Exchange theory

Figure 11.23: Contact Exchange theory

90 11.8.2 Active Absorption is called as anion respiration or salt . Based on this observation Absorption of ions against the respiration (1950 and 1954) proposed concentration gradient with the Lundegardh cytochrome pump theory which is based expenditure of metabolic energy is called on the following assumptions: . In plants, the vacuolar active absorption i. The mechanism of anion and cation sap shows accumulation of anions and absorption are different. cations against the concentration gradient ii. Anions are absorbed through which cannot be explained by theories of cytochrome chain by an active process, passive absorption. Mechanism of active cations are absorbed passively. absorption of salts can be explained iii. An oxygen gradient responsible through Carrier concept. for oxidation at the outer surface of the Carrier Concept: membrane and reduction at the inner surface. This concept was proposed by Van den Honert in 1937. The cell membrane is According to this theory, the enzyme largely impermeable to free ions. However, dehydrogenase on inner surface is responsible for the formation of protons (H+) and the presence of carrier molecules in the membrane acts as a vehicle to pick up or electrons (e–). As electrons pass outward through electron transport chain there is a bind with ions to form carrier-ion-complex, which moves across the membrane. On the corresponding inward passage of anions. Anions are picked up by oxidized cytochrome inner surface of the membrane, this complex oxidase and are transferred to other members breaks apart releasing ions into cell while of chain as they transfer the electron to the carrier goes back to the outer surface to pick next component (Figure 11.26). up fresh ions (Figure 11.25). The theory assumes that cations (C+) move passively along the electrical gradient created by the accumulation of anions (A–) at the inner surface of the membrane.

Figure 11.25: Carrier Concept A- - 2+ 3+ 2+ - The concept can be explained using two A Fe Fe Fe A A- - - 3+ 2+ 3+ e theories: e Fe Fe Fe A- A-

INSIDE 1. Lundegardh’s Cytochrome Pump OUTSIDE H Dehydrogenase Reactions Theory: ¼O2 Lundegardh and Burstrom (1933) ½HO - observed a correlation between respiration 2 H + + and anion absorption. When a plant is c c transferred from water to a salt solution Cytochrome Pump theory the rate of respiration increases which Figure 11.26:

91 Main defects of the above theory are: cation concentration would be greater in the (i) Cations also induce respiration. internal than in the external solution. This (ii) Fails to explain the selective uptake electrical balance or equilibrium controlled of ions. by electrical as well as diffusion phenomenon is known as the . (iii) It explains absorption of anions Donnan equilibrium only. Summary 2. Bennet-Clark’s Protein-Lecithin Theory: There are two types of transports namely In 1956, Bennet-Clark proposed that the carrier could be a protein associated with short and long distance in plants to translocate sap and solutes. Based on phosphatide called as lecithin. The carrier energy requirement, the transport may is amphoteric (the ability to act either as an acid or a base) and hence both cations and either be passive or active. The process of anions combine with it to form Lecithin- diffusion, facilitated diffusion, imbibition ion complex in the membrane. Inside and osmosis are driven by concentration the membrane, Lecithin-ion complex gradient like a ball rolling down to a slope is broken down into phosphatidic acid and hence, no energy is needed. The water and choline along with the liberation absorbed (either active or passive) from of ions. Lecithin again gets regenerated the soil by root hairs must reach the xylem from phosphatidic acid and choline in the for further transportation. There are three presence of the enzyme choline acetylase possible routes to reach the xylem from root and choline esterase (Figure 11.27). ATP hairs. They are i) apoplast ii) symplast and/ is required for of lecithin. or iii) transmembrane. Various theories explain the path of sap in the xylem and

+ Dixon’s Cohesion-tension theory is the C+ Phosphatidic C C+ Lecithinase Acid most accepted one. Transpiration is mostly Lecithin _ _ Choline _ A A A carried out by stomata, which has guard Choline Esterase Choline Acetylase ATP cells. The general mechanism of stomatal INSIDE

OUTSIDE Acetyl Choline movement is based on entry and exit of water molecules in guard cells. Many theories are there to explain how water Figure 11.27: Protein-Lecithin theory enters and exits from guard cells. The 11.8.3 Donnan equilibrium theory of potassium transport enumerates Within the cell, some of the ions never two different reactions separately run for diffuse out through the membrane. They opening and closing of stomata. Contrary are trapped within the cell and are called to ascent of sap by xylem in an upward fixed ions. But they must be balanced by direction, the path of solute which the ions of opposite charge. Assuming that consists of the photosynthetic products a concentration of fixed anions is present is always in phloem and translocate inside the membrane, more cations would be multidirectional. The point of origin of absorbed in addition to the normal exchange translocation is photosynthetic leaves to maintain the equilibrium. Therefore, the which are the source. On the other

92 hand, point of utilization is called 5. Munch hypothesis is based on sink. According to Munch mass flow a. Translocation of food due to TP hypothesis, the solutes move along the gradient and imbibition force concentration gradient in a bulk flow. b. Translocation of food due to TP Although minerals are dissolved in c. Translocation of food due to soil water, they do not tend together imbibition force with water to enter the root hairs during d. None of the above absorption of water. Mineral absorption is 6. If the concentration of salt in the soil is independent of water absorption. Minerals too high and the plants may wilt even are absorbed either actively or passively. if the field is thoroughly irrigated. Explain Evaluation 7. How phosphorylase enzyme 1. In a fully turgid cell open the stomata in starch sugar a. DPD = 10 atm; OP = 5 atm; interconversion theory? TP = 10 atm 8. List out the non-photosynthetic b. DPD = 0 atm; OP = 10 atm; parts of a plant that need a supply of TP = 10 atm sucrose? c. DPD = 0 atm; OP = 5 atm; 9. What are the parameters which TP = 10 atm control water potential? d. DPD = 20 atm; OP = 20 atm; 10. An artificial cell made of selectively TP = 10 atm permeable membrane immersed in a 2. Which among the following is correct? beaker (in the figure). Read the values i. apoplast is fastest and operate in and answer the following questions? nonliving part ii. Transmembrane route includes vacuole iii. symplast interconnect the nearby cell through plasmadesmata iv. symplast and transmembrane route a. Draw an arrow are in living part of the cell to indicate the direction of water a. i and ii b. ii and iii movement c. iii and iv d. i, ii, iii, iv b. Is the solution outside the cell isotonic, hypotonic or hypertonic? 3. What type of transpiration is possible c. Is the cell isotonic, hypotonic or in the Opuntia? hypertonic? a. Stomatal b. Lenticular d. Will the cell become more flaccid, c. Cuticular d. All the above more turgid or stay in original size? 4. Stomata of a plant open due to e. With reference to artificial cell a. Influx of K+ b. Efflux of K+ state, the process is endosmosis or c. Influx of Cl– d. Influx of OH– exosmosis? Give reasons

93 t ICT Corner Membrane transport

Let’s play with membrane proteins.

Steps • Open PhET: Method 1: By scanning the QR Code given Method 2: Through Google – Open PhET by typing PhET • Select play with simulation & enter • Click Biology – select Membrane Channels & run • Select Membrane channel in PhET • Select round molecule and pump it by pressing red button in one column • Select square molecule and pump it by pressing the same action • Observe the movement of molecules across membrane

Activity • Use leakage channel and gated channel in closed and open position and observe the molecules movement.

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94 Chapter 12 Mineral

Learning Objectives A solution to Pollution The learner will be able to, • Recognise the need of mineral nutrition. Pebble Gunny bags • Analyse the classification and styrofoam criteria for essential minerals. Bamboo tray • Learn the techniques of Hydroponics and Aeroponics. • Correlate different types of special Root hairs Microbes modes of nutrition. • Ability to recall and analyse nitrogen . A new solution has come up for high Chapter Outline nutrient pollution and eutrophication 12.1 Classification of Minerals in surface . Floating Treatment Wetlands (FTWs) offer promising 12.2 Functions, mode of absorption, deficiency symptoms of solution and it is a built structure Macronutrients which measures around 3,000 sq.ft and comprises four layers: floatable 12.3 Functions, mode bamboo at base, styrofoam second of absorption and layer, a third layer of gunny bags with deficiency symptoms of gravels and final layer to support Micronutrients cleaning agents (plants). Native plants 12.4 Deficiency and symptoms including Vetivers, Citronella, Tulsi Critical Concentration and Toxicity 12.5 and Withania are being researched of minerals for use as cleaning agents. FTW works 12.6 Hydroponics and Aeroponics on the principle of Hydroponics 12.7 Nitrogen Fixation which is explained in this chapter. Microbes grown on the roots of these 12.8 Nitrogen Cycle and Nitrogen Metabolism plants break down and consume in water and reduce pollution. 12.9 Special Modes of Nutrition

95 As a traveller you would have got 12.1 Classification of minerals a chance to observe the plants. It is an interesting fact that all plants are not 12.1.1 Classification of minerals based unique. Just spend some time to listen on their quantity to nature. You can notice plants with Essential elements are classified as attractive leaves, flowers and fruits. Macronutrients, Micronutrients and Can you say all plants are healthy and Unclassified minerals based on their uniform in growth? Some plants are not requirements. Essential minerals which healthy and show symptoms like texture are required in higher concentration are changes, stunted growth, chlorosis, called Macronutrients. Essential minerals and so on. Can you tell what is the reason which are required in less concentration for all these symptoms? It may be due to called are as Micronutrients. infection of microbial pathogens or climatic Minerals like Sodium, Silicon, Cobalt factors or due to mineral deficiency. and Selenium are not included in the list In this chapter we are going to learn about classification of minerals, their Historical events in mineral functions, deficiency diseases and nutrition symptoms, nitrogen metabolism and special modes of nutrition. Further, Van Helmont (1648) – made first how can these ideas help us to improve observation of mineral nutrition, in agriculture? noticed over a period of 5 years soil lost only 56 g in nourishing a seedling Plants naturally obtain nutrients from into tree. Increase in organic substance atmosphere, water and soil. Carbon, comes from water alone. hydrogen and oxygen are called as skeletal elements and constitute about 94% of Wood word (1699) – Soil provides mineral nutrients required for their dry weight. These elements play an growth. important role in the formation of organic compounds such as carbohydrates, fats De Saussure (1804) – plant growth and protein. These non-mineral elements depends on nitrogen and other are obtained from air and water. Minerals elements absorbed by roots from soil. are classified based on essentiality. Arnon Liebig (1840) – gave the “law and Stout (1939) gave criteria required for of minimum” which states that essential minerals: productivity of soil depends on 1. Elements necessary for growth and amount of essential elements present development. in minimum quantity. (1860) – Demon- 2. They should have direct role in the Julius Von Sachs strated growing a plant in a defined metabolism of the plant. nutrient solution. 3. It cannot be replaced by other elements. William Frederick Goerick (1940) – 4. Deficiency makes the plants impossible Gave the term Hydroponics and com- to complete their vegetative and mercial technique. reproductive phase.

96 Table 12.1: Mineral Types Macro nutrients Micro nutrients Unclassified minerals Excess than 10 mmole Kg-1 Less than 10 mmole Kg-1 Required for some plants in tissue concentration or in tissue concentration or in trace amounts and have 0.1 to 10 mg per gram of equal or less than 0.1 mg some specific functions. dry weight. per gram of dry weight.

Example: C, H, O, N, P, K, Example: Fe, Mn, Cu, Mo, Example: Sodium, Cobalt, Ca, Mg and S Zn, B, Cl and Ni Silicon and Selenium of essential nutrients but are required by mobile minerals and 2. Relatively some plants, these minerals are placed immobile minerals (Figure 12.1). in the list of unclassified minerals. These minerals play specific roles for example, a. Actively mobile minerals Silicon is essential for pest resistance, Nitrogen, Phosphorus, Potassium, prevent water lodging and aids cell wall Magnesium, Chlorine, Sodium, Zinc and formation in Equisetaceae (Equisetum), Molybdenum. Cyperaceae and Gramineae (Table 12. 1). Deficiency symptoms first appear on old and senescent leaves due to active 12.1.2 Classification of minerals based movement of minerals to younger leaves. on mobility b. Relatively immobile minerals If you observe where the deficiency Calcium, Sulphur, Iron, Boron and symptoms appear first, you can notice Copper shows deficiency symptoms first differences in old and younger leaves. It is that appear on young leaves due to the mainly due to mobility of minerals. Based immobile nature of minerals on this, they are classified into 1. Actively 12.1.3 Classification of minerals based on their functions a. Structural component minerals: Minerals like Carbon, Hydrogen, Oxygen and Nitrogen b. Enzyme function: Molybdenum (Mo) X is essential for nitrogenase enzyme during reduction of atmospheric Mobile minerals Immobile minerals nitrogen into ammonia. Zinc (Zn) Necrosis Minerals Chlorosis is an important activator for alcohol dehydrogenase and carbonic Movement of Minerals anhydrase. Magnesium (Mg) is the X Movement blocked activator for RUBP carboxylase- Figure 12.1: Mobility of Minerals oxygenase and PEP carboxylase.

97 Nickel (Ni) is a constituent of urease balance by ion-exchange. It is absorbed and hydrogenase. as K1 ions. c. Osmotic Potential: Potassium (K) Deficiency symptoms: Marginal plays a key role in maintaining osmotic chlorosis, necrosis, low cambial activity, potential of the cell. The absorption loss of apical dominance, lodging in of water, movement of stomata and and curled leaf margin. turgidity are due to osmotic potential. 4. Calcium (Ca): It is involved in synthesis d. Energy components: Magnesium of calcium pectate in middle lamella, (Mg) in chlorophyll and phosphorous mitotic spindle formation, mitotic (P) in ATP. cell division, permeability of cell membrane, lipid metabolism, activation 12.2 Functions, mode of absorption of phospholipase, ATPase, amylase and and deficiency symptoms of activator of adenyl kinase. It is absorbed macronutrients as Ca21 exchangeable ions. Macronutrients, their functions, their Deficiency symptoms: Chlorosis, mode of absorption, deficiency symptoms necrosis, stunted growth, premature and deficiency diseases are discussed here: fall of leaves and flowers, inhibit seed 1. Nitrogen (N): It is required by the formation, Black heart of , plants in greatest amount. It is an Hooked leaf tip in Sugar beet, Musa essential component of proteins, and Tomato. nucleic acids, amino acids, vitamins, 5. Magnesium (Mg): It is a constituent hormones, alkaloids, chlorophyll and of chlorophyll, activator of enzymes cytochrome. It is absorbed by the of carbohydrate metabolism (RUBP plants as nitrates (NO ). 3 Carboxylase and PEP Carboxylase) Chlorosis, Deficiency symptoms: and involved in the synthesis of DNA stunted growth, anthocyanin formation. and RNA. It is essential for binding of Constituent of 2. Phosphorus (P): ribosomal sub units. It is absorbed as cell membrane, proteins, nucleic Mg21 ions. acids, ATP, NADP, phytin and sugar 1 Deficiency symptoms: Inter veinal phosphate. It is absorbed as H2PO4 2 chlorosis, necrosis, anthocyanin and HPO4 ions. (purple) formation and Sand drown of Deficiency symptoms: Stunted growth, anthocyanin formation, tobacco. necrosis, inhibition of cambial activity, 6. Sulphur (S): Essential component affect root growth and fruit ripening. of amino acids like cystine, cysteine 3. Potassium (K): Maintains turgidity and methionine, constituent of and osmotic potential of the cell, coenzyme A, Vitamins like biotin and opening and closure of stomata, thiamine, constituent of proteins and phloem translocation, stimulate ferredoxin.plants utilise sulphur as activity of enzymes, anion and cation 2 sulphate (SO4 ) ions.

98 Deficiency symptoms: Chlorosis, in many plants. Example: Boron is essential anthocyanin formation, stunted growth, for translocation of sugars, molybdenum rolling of leaf tip and reduced nodulation is involved in nitrogen metabolism and in . zinc is needed for biosynthesis of . Here, we will study about the role of micro nutrients, their functions, their mode of NPK Fertilizers absorption, deficiency symptoms and It consists of nitrogen, deficiency diseases. phosphate with 1. Iron (Fe): Iron is required lesser potassium in different than macronutrient and larger than proportions. The number labelled on micronutrients, hence, it can be the bags as 15-15-15 indicates N, P & placed in any one of the groups. Iron is K in equal proportions. an essential element for the synthesis of chlorophyll and carotenoids. It is the component of cytochrome, ferredoxin, flavoprotein, formation Chelating Agents of chlorophyll, porphyrin, activation EDTA (Chemical Chelating Agent) of catalase, peroxidase enzymes. It is Plants which are growing in alkaline absorbed as ferrous (Fe21) and ferric soil when supplied with all nutrients (Fe31) ions. Mostly fruit trees are including iron will show iron sensitive to iron. deficiency. To rectify this, we have to Deficiency: Interveinal Chlorosis, make iron into a soluble complex by formation of short and slender stalk and adding a chelating agent like EDTA inhibition of chlorophyll formation. (Ethylene Diamine Tetra Acetic acid) Activator of to form Fe-EDTA. 2. Manganese (Mn): carboxylases, oxidases, dehydrogenases Siderophores (Biological Chelating and kinases, involved in splitting of agent) water to liberate oxygen (photolysis). It Siderophores (iron carriers) are is absorbed as manganous (Mn21) ions. Iron chelating agents produced by Interveinal chlorosis, bacteria. They are used to chelate Deficiency: grey spot on oats leaves and poor root ferric Iron (Fe31) from environment system. and host. 3. Copper (Cu): Constituent of plastocyanin, component of 12.3 Functions, mode of absorption phenolases, tyrosinase, enzymes and deficiency symptoms of involved in redox reactions, synthesis of micronutrients ascorbic acid, maintains carbohydrate Micronutrients even though required and nitrogen balance, part of oxidase in trace amounts are essential for the and cytochrome oxidase. It is absorbed metabolism of plants. They play key roles as cupric (Cu21) ions.

99 Deficiency: Die back of citrus, Reclamation of cereals and Calmodulin legumes, chlorosis, necrosis and Calmodulin is a Ca21 Exanthema in Citrus. modulating protein in eukaryotic cells. It 4. Zinc (Zn): Essential for the synthesis of Indole acetic acid (Auxin) activator of is a heat stable protein involved in carboxylases, alcohol dehydrogenase, fine metabolic regulations. lactic dehydrogenase, glutamic acid dehydrogenase, carboxy peptidases 12.4 Deficiency diseases and symptoms and tryptophan synthetase. It is The following table (Table 12.2) gives absorbed as Zn21 ions. you an idea about Minerals and their Deficiency: Little leaf and mottle leaf Deficiency symptoms: due to deficiency of auxin, Inter veinal chlorosis, stunted growth, necrosis and Khaira disease of rice. Activity 5. Boron (B): Translocation of Collect leaves showing mineral carbohydrates, uptake and utilisation deficiency. Tabulate the symptoms of Ca11, germination, nitrogen like Marginal Chlorosis, Interveinal metabolism, fat metabolism, cell Chlorosis, Necrotic leaves, elongation and differentiation. It is Anthocyanin formation in leaf, Little absorbed as borate BO32 ions. leaf and Hooked leaf. (Discuss with of root and shoot Deficiency: your teacher about the deficiency of tips, premature fall of flowers and minerals) fruits, brown heart of beet root, internal cork of and fruit cracks. 6. Molybdenum (Mo): Component of nitrogenase, nitrate reductase, involved 12.5 Critical concentration and toxicity in nitrogen metabolism, and nitrogen of minerals fixation. It is absorbed as molybdate (Mo21) ions. 12.5.1 Critical Concentration To increase the productivity and also Deficiency: Chlorosis, necrosis, delayed flowering, retarded growth to avoid mineral toxicity knowledge of and whip tail disease of cauliflower. critical concentration is essential. Mineral nutrients lesser than critical concentration It is involved in Anion – 7. Chlorine (Cl): cause deficiency symptoms. Increase Cation balance, cell division, photolysis of mineral nutrients more than the of water. It is absorbed as Cl2 ions. normal concentration causes toxicity. A Deficiency: Wilting of leaf tips concentration, at which 10 % of the dry weight of tissue is reduced, is considered 8. Nickel (Ni): Cofactor for enzyme urease and hydrogenase. as toxic. Figure 12.2 explains about Critical Concentration. Deficiency: Necrosis of leaf tips.

100 Table 12.2: Deficiency diseases and Symptoms Name of the deficiency Deficiency minerals disease and symptoms 1. Chlorosis (Overall) Nitrogen, Potassium, Magnesium, Sulphur, Iron, Manganese, Zinc and Molybdenum.

a. Interveinal chlorosis Magnesium, Iron, Manganese and Zinc b. Marginal chlorosis Potassium 2. Necrosis (Death of the tissue) Magnesium, Potassium, Calcium, Zinc, Molybdenum and Copper.

3. Stunted growth Nitrogen, Phosphorus, Calcium, Potassium and Sulphur.

4. Anthocyanin formation Nitrogen, Phosphorus, Magnesium and Sulphur

5. Delayed flowering Nitrogen, Sulphur and Molybdenum 6. Die back of shoot, Reclamation disease, Copper Exanthema in citrus (gums on bark)

7. Hooked leaf tip Calcium 8. Little Leaf Zinc 9. Brown heart of turnip and Boron Internal cork of apple

10. Whiptail of cauliflower and cabbage Molybdenum 11. Curled leaf margin Potassium

10% Reduction 12.5.2 Mineral Toxicity In Plant Growth

Adequate Zone a. Manganese toxicity

Toxic Increased Concentration of Manganese Zone will prevent the uptake of Fe and Mg, Transition Zone prevent translocation of Ca to the shoot apex and cause their deficiency. The symptoms of manganese toxicity are appearance of brown spots surrounded by Deficient Zone chlorotic veins. Critical Nutrient Toxic Growth as a % of Maximum Rate Concentration Concentration b. Aluminium Toxicity Aluminium toxicity causes precipitation Concentration of Nutrient in Plant Tissue of nucleic acid, inhibition of ATPase, Figure 12.2: Critical Concentration

101 hydroponics. In hydroponics roots are Iron and Manganese toxicity immersed in the solution containing Iron and Manganese exhibit nutrients and air is supplied with help competitive behaviour. Deficiency of of tube (Figure 12.3). Fe and Mn shows similar symptoms. Aeroponics: This technique was Iron toxicity will affect absorption of developed by Soifer Hillel and David manganese. The possible reason for Durger. It is a system where roots iron toxicity is excess usage of chelated are suspended in air and nutrients iron in addition with increased acidity are sprayed over the roots by a motor of soil (PH less than 5.8) Iron and driven rotor (Figure 12.4). manganese toxicity will be solved by using fertilizer with balanced ratio of Fe and Mn.

Suspended inhibition of cell division and binding of root plasma membrane with Calmodulin. Mist chamber For theories regarding, translocation Nutrient of minerals please refer Chapter- 11. Solution Spray rotor

12.6 Hydroponics and Aeroponics Figure 12.4: Aeroponics 1. Hydroponics or Soilless culture: Von Sachs developed a method of 12.7 Nitrogen Fixation growing plants in nutrient solution. Inspiring act of nature is self-regulation. The commonly used nutrient solutions As all living act as tools for are Knop solution (1865) and Arnon bio geo chemical cycles, nitrogen cycle is and Hoagland Solution (1940). highly regulated. Life on earth depends Later the term Hydroponics was on nitrogen cycle. Nitrogen occurs in coined by Goerick (1940) and he also atmosphere in the form of N2 (N{N), two introduced commercial techniques for nitrogen joined together by strong

Air pump

Buoyant pads to support the plants Water circulation pump

Nutrient Air bubble solution Air pipe

Figure 12.3: Hydroponics

102 12.7.2 Biological nitrogen fixation Activity Symbiotic bacterium like Rhizobium fixes Preparation of Solution Culture to atmospheric nitrogen. Cyanobacteria find out Mineral Deficiency found in Lichens, Anthoceros, Azolla and coralloid roots of also fix nitrogen. 1. Take a glass jar or polythene bottle Cycas non-symbiotic (free living bacteria) like and cover with black paper (to also fix nitrogen. prevent algal growth and roots Clostridium reacting with light). a. Symbiotic nitrogen fixation 2. Add nutrient solution. i. Nitrogen fixation with nodulation 3. Fix a plant with the help of split Rhizobium bacterium is found in leguminous cork. plants and fix atmospheric nitrogen. This 4. Fix a tube for aeration. kind of symbiotic association is beneficial for both the bacterium and plant. Root nodules 5. Observe the growth by adding are formed due to bacterial infection. specific minerals. Rhizobium enters into the host cell and proliferates, it remains separated from the triple covalent bonds. The process of host cytoplasm by a membrane (Figure 12.6). converting atmospheric nitrogen (N2) into ammonia is termed as nitrogen fixation. Stages of Root nodule formation: Nitrogen fixation can occur by two 1. plants secretes phenolics methods: 1. Biological; 2. Non-Biological which attracts Rhizobium. (Figure 12.5). 2. Rhizobium reaches the rhizosphere and enters into the root hair, infects 12.7.1 Non – Biological nitrogen fixation the root hair and leads to curling of • Nitrogen fixation by chemical process root hairs. in industry. 3. Infection thread grows inwards and • Natural electrical discharge during separates the infected tissue from lightening fixes atmospheric nitrogen. normal tissue.

NITROGEN FIXATION

Non-Biological Biological

Industrial Lightening Non symbiotic Symbiotic

Legume Non legume

Figure 12.5: Nitrogen fixation

103 b. Non-symbiotic Nitrogen fixation Free living bacteria and fungi also fix atmospheric nitrogen.

Aerobic Azotobacter, Beijer- neckia and Derxia Anaerobic Clostridium Photosynthetic Chlorobium and Rhodospirillum Figure 12.6: Rhizobium (Bacteroid) in Chemosynthetic Disulfovibrio root nodule Free living fungi Yeast and Pullularia 4. A membrane bound bacterium is Cyanobacteria Nostoc, Anabaena formed inside the nodule and is called and Oscillatoria. bacteroid. 5. Cytokinin from bacteria and auxin 12.8 Nitrogen cycle and nitrogen from host plant promotes cell division metabolism and leads to nodule formation 12.8.1 Nitrogen cycle This cycle consists of Activity following stages: • Collect roots of legumes with root 1. Fixation of nodules. atmospheric nitrogen • Take cross section of the root nodule. Di-nitrogen molecule from the atmosphere • Observe under microscope. Discuss progressively gets reduced by addition of your observations with your teacher. a pair of hydrogen atoms. Triple bond between two nitrogen atoms (N{N) are cleaved to produce ammonia (Figure 12.7). Non-Legume nitrogen fixation process requires Alnus and Casuarina contain the Nitrogenase enzyme complex, Minerals bacterium Frankia. Psychotria contains (Mo, Fe and S), anaerobic condition, ATP, the bacterium Klebsiella. electron and glucose 6 phosphate as H1 donor. Nitrogenase enzyme is active only ii. Nitrogen fixation without nodulation in anaerobic condition. To create this The following plants and prokaryotes anaerobic condition a pigment known are involved in nitrogen fixation. as leghaemoglobin is synthesized in the Lichens - Anabaena and Nostoc nodules which acts as oxygen scavenger and Anthoceros - Nostoc removes the oxygen. Nitrogen fixing bacteria in root nodules appears pinkish due to the Azolla - Anabaena azollae presence of this leghaemoglobin pigment. Cycas - Anabaena and Nostoc

104 Enzyme Dinitrogen 3. Nitrate Nitrogenase N Molecule The process by which nitrate is reduced N to ammonia is called nitrate assimilation and occurs during nitrogen cycle. N

N 2 Nitrate reductase 2 NO3 NO2 Mo Nitrite reductase NO 2 NH 1 N 2 3 H Cu, Fe N H

H 4. Ammonification N H of organic nitrogen N H (proteins and amino acids) from dead H plants and animals into ammonia is called H H ammonification. Organisim involved N H in this process are Bacillus ramosus and N H H Bacillus vulgaris. H 5. Denitrification H Nitrates in the soil are converted back into N H H atmospheric nitrogen by a process called H denitrification. Bacteria involved in this N H H process are Pseudomonas, Thiobacillus Nitrogenase Ammonia and Bacillus subtilis. Figure 12.7: Nitrogenase enzyme function Nitrate Pseudomonas Molecular Nitrogen 2 Overall equation: (NO3 ) (N2) N 1 8e2 1 8H1 1 16ATP 2 The overall process of nitrogen cycle is 2NH 1 1 H 1 16ADP 1 16 Pi 3 2 given in Figure 12.8. 2. Nitrification 1 12.8.2 Nitrogen Metabolism Ammonia (NH3 ) is converted into Nitrite 2 (NO2 ) by Nitrosomonas bacterium. Ammonium Assimilation (Fate of Nitrite is then converted into Nitrate Ammonia) 2 (NO3 ) by Nitrobacter bacterium. Ammonia is converted into amino acids Plants are more adapted to absorb nitrate by the following processes: (NO 2) than ammonium ions from the soil. 3 1. Reductive amination

1 Nitrosomonas 2 1 Glutamic acid or glutamate is formed by 2 NH3 1 3 O2 2 NO2 1 2 H 1 2H2O reaction of ammonia with α-ketoglutaric 2 Nitrobacter - 2 NO2 1 O2 2 NO3 acid.

105

3. Catalytic Amination: (GS/GOGAT Pathway) Glutamate combines with ammonia to form the amide glutamine.

Glutamine Synthetase (GS) 1 Glutamate 1 NH4 Glutamine. ATP ADP 1 Pi Glutamine reacts with α ketoglutaric acid to form two molecules of glutamate.

GOGAT (enzyme) Neottia Monotropa Glutamine 1 α Ketoglutaric acid 2 Glutamate (Bird's Nest Orchid) (Indian Pipe) (2- oxoglutarate) NADH1H1 NAD1 Figure 12.9: Saprophytic Mode of nutrition (GOGAT- Glutamine-2-Oxoglutarate aminotransferase) 12.9.2 Parasitic mode of nutrition in angiosperms 12.9 Special modes of nutrition Organisms deriving their nutrient from Nutrition is the process of uptake and another (host) and causing utilization of nutrients by living organisms. disease to the host are called parasites. There are two main types such as a. Obligate or Total parasite - Completely autotrophic and heterotrophic nutrition. depends on host for their survival and Autotrophic nutrition is further divided produces haustoria. into and photosynthetic chemosynthetic i. Total stem parasite: The leafless stem nutrition. Heterotrophic nutrition is twine around the host and produce further divided into saprophytic, parasitic, haustoria. Example: Cuscuta (Dodder), symbiotic and insectivorous type. In this a rootless plant growing on Zizyphus, topic you are going to learn about special Citrus and so on. mode of nutrition. ii. Total root parasite: They do not 12.9.1 Saprophytic mode of nutrition in have stem axis and grow in the roots of host plants produce haustoria. angiosperms Example: Rafflesia, Orobanche and Saprophytes derive nutrients from dead Balanophora. and decaying matter. Bacteria and - Plants of this group are main saprophytic organisms. Some b. Partial parasite contain chlorophyll and synthesize angiosperms also follow saprophytic mode carbohydrates. Water and mineral of nutrition. Example: Neottia. Roots of requirements are dependent on host plant. Neottia (Bird’s Nest Orchid) associate with mycorrhizae and absorb nutrients i. Partial Stem Parasite: Example: and (Mistletoe) as a saprophyte. Monotropa (Indian Loranthus Viscum Pipe) grow on humus rich soil found in Loranthus grows on fig and mango thick forests. It absorbs nutrient through trees and absorb water and minerals mycorrhizal association (Figure 12.9). from xylem.

107 Figure 12.11: Symbiotic mode of nutrition Nostoc associates with its coralloid roots. (Figure 12.11).

12.9.4 Insectivorous mode of nutrition Plants which are growing in nitrogen Parasitic Mode of Nutrition Figure 12.10: deficient areas develop insectivorous to resolve nitrogen deficiency. ii. : Example: Partial root parasite a. Nepenthes (Pitcher plant): Pitcher is Santalum album (Sandal wood tree) a modified leaf and contains digestive in its juvenile stage produces haustoria enzymes. Rim of the pitcher is provided which grows on roots of many plants with glands and acts as an attractive (Figure 12.10). lid. When insect is trapped, proteolytic enzymes will digest the insect. 12.9.3 Symbiotic mode of Nutrition b. Drosera (Sundew): It consists of long a. Lichens : It is a mutual association of club shaped tentacles which secrete Algae and Fungi. Algae prepares food sticky digestive fluid which looks like a and fungi absorbs water and provides sundew. structure. c. Utricularia (Bladder wort): Submerged b. Mycorrhizae : Fungi associated with plant in which leaf is modified into a roots of higher plants including bladder to collect insect in water. Gymnosperms. Example: Pinus. d. Dionaea (Venus fly trap): Leaf of this c. Rhizobium and Legumes: This symbiotic plant modified into a colourful trap. Two association fixes atmospheric nitrogen folds of lamina consist of sensitive trigger d. Cyanobacteria and Coralloid Roots: hairs and when insects touch the hairs it This association is found in Cycas where will close (Figure 12.12).

108 higher concentration and micro nutrients (Fe, Mn, Cu, Zn, B, Mo, Cl and Ni) are required in lesser concentration. Minerals like Sodium, Cobalt, Silicon and Selenium are required by some plants for specific functions and such minerals are grouped as unclassified minerals. Actively mobile elements are N, P, K, Mg, Cl, Na, Zn and Mo. The deficiency symptoms for these minerals first appear on old and senescent leaves due to active movement of minerals to younger leaves. Relatively immobile elements are Ca, S, Fe, B and Cu. In such minerals, deficiency symptoms first appear on young leaves due to immobile nature. Minerals and their deficiency symptoms include chlorosis (loss of chlorophyll Insectivorous mode of Figure 12.12: pigments), necrosis (death of tissue), nutrition anthocyanin formation, die back of shoot, exanthema, hooked leaf tip, whiptail and Lichens are indicators so on. A concentration at which 10% of

of SO2 pollution and dry weight is reduced is considered as a pioneer species in critical concentration. Minerals used in xeric succession. excess concentration become toxic. Soil less cultivation alleviates problems due to mineral deficiency. It includes Check your grasp! hydroponics and aeroponics. Hydroponics Mineral X required for the activation is a method of growing plants in a of enzyme nitrogenase, Mineral Y nutrient solution. Aeroponics is the involved in transport of sugar and technique in which roots are suspended Mineral Z required for maintaining over the nutrient medium in air and ribosome structure. Identify X, Y and Z. nutrient sprayed over the roots by motor driven rotor. Nitrogen is an important requirement for normal growth and Summary functioning of a plant. Nitrogen fixing Sources of minerals for plants are organisms fix nitrogen from atmosphere atmosphere, water and soil. Minerals are naturally through symbiotic and non- classified based on their quantity, mobility symbiotic modes. Special modes of and functions. Macro nutrients (C, H, O, nutrition are seen in plant which grew in N, P, K, Ca, Mg and S) are required in nutrient deficient soils and the character becomes permanent.

109 Evaluation 1. Identify correct match. 1. Die back disease of citrus - (i) Mo 2. Whip tail disease - (ii) Zn 3. Brown heart of turnip - (iii) Cu 4. Little leaf - (iv) B 5. Identify the correct statement a. 1 (iii) 2 (ii) 3 (iv) 4 (i) i. Sulphur is essential for amino acids b. 1 (iii) 2 (i) 3 (iv) 4 (ii) Cystine and Methionine ii. Low level of N, K, S and Mo affect c. 1 (i) 2 (iii) 3 (ii) 4 (iv) the cell division d. iii) 2 (iv) 3 (ii) 4 (i) 1 ( iii. Non-leguminous plant Alnuswhich 2. If a plant is provided with all mineral contain bacterium Frankia nutrients but, Mn concentration is iv. Denitrification carried out by increased, what will be the deficiency? nitrosomonas and nitrobacter. a. Mn prevent the uptake of Fe, Mg a. I, II are correct but not Ca b. I, II, III are correct b. Mn increase the uptake of Fe, Mg c. I only correct and Ca d. all are correct c. Only increase the uptake of Ca 6. The nitrogen is present in the d. Prevent the uptake Fe, Mg, and Ca atmosphere in huge amount but 3. The element which is not remobilized? higher plants fail to utilize it. Why? a. Phosphorous b. Potassium 7. Why is that in certain plants c. Calcium d. Nitrogen deficiency symptoms appear first in 4. Match the correct combination. younger parts of the plants while in others, they do so in mature organs? Minerals Role 8. Plant A in a nutrient medium shows A Molybdenum 1 Chlorophyll whiptail disease plant B in a nutrient B Zinc 2 Methionine medium shows a little leaf disease. Identify mineral deficiency of plant A C Magnesium 3 Auxin and B? D Sulphur 4 Nitrogenase 9. Write the role of nitrogenase enzyme in nitrogen fixation? a. A-1 B-3 C-4 D-2 10. Explain the insectivorous mode of nutrition in angiosperms? b. A-2 B-1 C-3 D-4 c. A-4 B-3 C-1 D-2 d. A-4 B-2 C-1 D-3

110 t ICT Corner Role of minerals in plant growth

Let’s try to make the plant blossom

Steps • Scan the QR code • Start a new game • Add lime • Test the Soil pH by test the sample press grows • Do it for combination of minerals

Activity • Change the combination of minerals and test the soil samples • Find the correct proportion of chemical and specific pH for flowering • Conclude your observations.

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111 Chapter 13 Photosynthesis

13.6 Absorption spectrum and Action Learning Objectives spectrum The learner will be able to, 13.7 Emerson’s experiments & Hill’s reaction • Learn the Ultra structure of 13.8 Modern concept of photosynthesis Chloroplast . 13.9 Photo-oxidation phase of light • Realise the importance of solar reaction energy and properties of light. 13.10 Photochemical phase of light • Acquire knowledge of Quantum, reaction Quantum yield and Quantum 13.11 Photophosphorylation requirement. 13.12 Chemiosmotic theory Dark reaction or C cycle • Develop curiosity for photosynthetic 13.13 3 Hatch & Slack Pathway or C Cycle experiments like Red drop, Emerson 13.14 4 Enhancement effect and Hill’s 13.15 CAM cycle or Crassulacean Acid Reaction. Metabolism Photorespiration or C Cycle • Analyse the pathway of electron- 13.16 2 Factors affecting photosynthesis PS I and PS II. 13.17 13.18 Photosynthesis in bacteria • Recognise the Photo-Oxidative and Photo Chemical Pathway. Life on earth is made up of organic • Develop skill in Photosynthetic compounds. How do we get these organic

pathways and ability to draw C3, compounds? Ultimately, plants are

C4, C2 and CAM cycle. the main source of all kinds of carbon compounds in this planet. We directly or indirectly depend on plants for this. Plants are the major machinery which produce Chapter Outline organic compounds like carbohydrates, 13.1 Historical events in photosynthesis , proteins, nucleic acids and other 13.2 Definition, Significance and Site of . photosynthesis Though man has reached the glory of 13.3 Photosynthetic pigments achievements still he is not able to imitate 13.4 Spectrum of electromagnetic the metabolic activities of plants which radiation produces energy resources and other Photosynthetic unit 13.5 biomolecules.

112 atmospheric oxygen and carbon A quest for future energy dioxide level. Photosynthesis consumes Hydrogen is considered as a promising atmospheric carbon dioxide which is energy vector for the next generation. continuously added by the respiration of It can be used for “green” electricity organisms. Photosynthesis is the major production or developing cogeneration endergonic reaction. In this chapter, systems such as fuel cells. The we will study about the energy yielding sustainability of its employment process of photosynthesis and various depends on the energy source used types of energy utilization processes to to synthesize it from hydrogen-rich produce carbohydrates. compounds such as water or biomass. The splitting of water in hydrogen and oxygen by means of solar radiation in 13.1 Historical Events in Photolysis is common in plants. Water Photosynthesis splitting is not an easy process to mimic • Van Helmont (1648) – Increase artificially but preliminary success is in organic substances comes from achieved so far. If young minds take water alone by growing a Willow tree up this as their research ambition a that gains weight but soil loses only revolution can be made in green energy. 2 ounces of the original weight. • Stephen Hales (1727) – Father of

In leaf cell Chloroplast Plant Physiology, Plants obtain O2 e- nourishment from air and light. PSII

e- • (1772) – Performed e- Joseph Priestley Hydrolysis experiments with candle, mice

HO2 H2 Fuel cell e- and Mint plant and concluded that H H 2 2 4e- vegetation purifies the air. 2H O + 2 4H +O2 Hydrogen storage • Jean-Ingen-Housz (1779) – Confirmed Priestley’s experiment The plants get energy from sun by that oxygen released by the plants is converting solar or radiant energy possible only in light. into chemical energy by the process • Lavoisier (1783) – Purifying gas of Photosynthesis, which acts as a produced by plants in sunlight is driving force for both biotic and abiotic Oxygen (Phlogiston) and noxious gas world. Photosynthesis produces 1700 produced by burning of candle (de million tonnes of dry matter per year Phlogiston) is Carbon di oxide. by fixing 75 × 1012 Kg of carbon every • (1804)- Explained the year. Photosynthetic organisms use Desaussure importance of water in the process of only 0.2 % of incident solar light on photosynthesis. earth. Carbohydrates produced by photosynthesis are the basic raw material • Dutrochet (1837) – Explained for respiration and also to produce the importance of Chlorophyll in many organic compounds. It maintains Photosynthesis.

113 • Von Mayer (1845) – Green plants • Melvin Calvin (1954) – Used 14 convert solar energy into chemical radioactive CO2 and traced path energy of organic matter. of carbon in the dark phase of

photosynthesis or C3 Cycle. CO2 1 H2O Organic matter 1 O2 • (1957) – Reported • (1845) – Organic matter of plants Emerson et al., Liebig existence of two photosystems was derived from CO . 2 • (1965) – Reported C • (1854) – Discovered Hatch and Slack 4 Julius Von Sachs pathway and CO fixation in C plants that product of photosynthesis was starch. 2 4 Green substance (chlorophyll) is located • Huber, Michel and Dissenhofer in special structures (Chloroplast). (1985) – Crystalized photosynthetic reaction centre of and • (1888)- Plotted action Rhodobacter T.W. Engelmann received the Nobel Prize in 1988. spectrum of photosynthesis • (1905) – Proposed Law of Blackman 13.2 Definition, Significance and Site Limiting factors. of Photosynthesis • Warburg (1920) – Used unicellular green algae Chlorella for the study of 13.2.1 Definition of Photosynthesis Photosynthesis. Photosynthesis is referred as photochemical • Van Neil (1931) – Oxygen released oxidation and reduction reactions during photolysis comes from water carried out with help of light, converting

and not from CO2. He also conducted solar energy into Chemical energy. It is experiments in Purple green bacteria and the most important anabolic process. demonstrated Photosynthesis. Plants and photosynthetic bacteria use Light simple raw materials like carbon dioxide 2H2A 1 CO2 Chlorophyll water and with the help of light energy (CH O) 1H O1 2A 2 n 2 synthesize carbohydrates and evolve In Green Sulphur bacteria H2S is oxygen. The overall chemical equation for the Hydrogen donor which releases photosynthesis is: Sulphur instead of oxygen. Light 6CO2 1 6H2O C6H12O6 1 6O2↑ • Emerson and Arnold (1932) – Chlorophyll Existence of light and dark reaction by Ruben and Kamen (1941) demonstrated flashing light experiments. six molecules of water as insufficient for

• R. Hill (1937) – Explained photolysis the of 6 molecules of O2 and with the help of isolated chloroplasts and modified the equation as: electron acceptors in the presence of light. Light 6CO2 1 12H2O C6H12O6 1 6 H2O1 6O2↑ Chlorophyll • Ruben and Kamen (1941) – Used 18O radioactive Oxygen to prove that Photosynthesis is a collection of oxygen evolves from water. oxidation and reduction reactions • Arnon, Allen and Whatley (1954) – (Redox reaction). 14 Used radioactive CO2 to show fixation Oxidation- Water is oxidised into oxygen

of CO2 by isolated chloroplast. (loss of electrons).

114 Reduction – CO2 is reduced into Carbohydrates (gain of electrons). Bioluminescence is the production and In some bacteria, oxygen is not emission of light by evolved and is called as and non-oxygenic a living organism. . Examples: anaerobic photosynthesis Bioluminescence is rare in true plants. Green sulphur, Purple sulphur and green filamentous bacteria. A team of MIT engineers have created living bioluminescent lamps out of 13.2.2 Significance of Photosynthesis watercress plants with the goal of one day 1. Photosynthetic organisms provide replacing conventional electrical lighting food for all living organisms on earth with the glowing greenery. either directly or indirectly. 2. It is the only natural process that A sac like membranous system called liberates oxygen in the atmosphere thylakoid or lamellae is present in stroma and balances the oxygen level. and they are arranged one above the other forming a stack of coin like structure called 3. Photosynthesis balances the oxygen (plural grana). Each chloroplast and carbon cycle in nature. granum contains 40 to 80 grana and each granum 4. Fuels such as coal, petroleum and consists of 5 to 30 thylakoids. other fossil fuels are from preserved Thylakoids found in granum are called photosynthetic plants. grana lamellae and in stroma are called 5. Photosynthetic organisms are the stroma lamellae. Thylakoid disc size is primary producers on which all 0.25 to 0.8 micron in diameter. A thinner consumers depend for energy. lamella called Fret membrane connects 6. Plants provide fodder, fibre, fire wood, grana. Pigment system I is located on timber, useful medicinal products outer thylakoid membrane facing stroma and these sources come by the act of and Pigment system II is located on inner photosynthesis. membrane facing lumen of thylakoid. Grana lamellae have both PS I and PS II 13.2.3 Site of Photosynthesis whereas stroma lamellae have only PS I. Chloroplasts are the main site of Chloroplast contains 30–35 Proteins, photosynthesis and both energy yielding 20–30% phospholipids, 5–10% chlorophyll, process (Light reaction) and fixation of 4–5% Carotenoids, 70S ribosomes, circular carbon dioxide (Dark reaction)that takes DNA and starch grains. Inner surface place in chloroplast. It is a double wall of lamellar membrane consists of small membrane bounded , discoid spherical structure called as Quantasomes. or lens shaped, 4–10 μm in diameter and Presence of 70S ribosome and DNA 1–33 μm in thickness. The membrane gives them status of semi-autonomy and is a unit membrane and space between proves endosymbiotic hypothesis which them is 100 to 200 A°. A colloidal and says chloroplast evolved from bacteria. proteinaceous matrix called stroma is Thylakoid contains pigment systems which present inside. produces ATP and NADPH 1 H1 using

115 (a) (b)

Figure 13.1: (a) 3D view of chloroplast (b) Sectional view of chloroplast solar energy. Stroma contains enzyme or photosynthetic bacteria which which reduces carbon dioxide into captures the light energy necessary for carbohydrates. In Cyanobacteria thylakoid photosynthesis (Table 13.1). lies freely in cytoplasm without envelope (Figure 13.1). 13.3.1 Chlorophyll Chlorophyll a is the primary pigment which acts as a reaction centre and all 13.3 Photosynthetic Pigments other pigments act as accessory pigments A photosynthetic pigment is a and trap solar energy and then transfer it pigment that is present in chloroplasts

Table 13.1: Types of Photosynthetic pigments Chlorophyll Carotenoids Phycobilins 1. Chlorophyll 'a' (C H O N Mg) 55 72 5 4 1. Carotene (C H ) – 1. Phycocyanin – – Green plants and 40 56 Lycopene (Red) Cyanobacteria Cyanobacteria 2. Xanthophyll (C H O )- 2. Chlorophyll 'b' (C H O N Mg) 40 56 2 55 70 6 4 Yellow colour – 2. Phycoerythrin – – Green algae and all higher Violaxanthin, Fucoxanthin Red Algae plants () and Lutein

3. Chlorophyll 'c' (C55H32O5N4Mg) – Dinoflagellates, Diatoms and Brown Algae 4. Chlorophyll 'd' – Red Algae 5. Chlorophyll 'e' – Xathophycean Algae 6. Bacteriochlorophyll 'a' 7. Bacteriochlorophyll 'b' 8. Chlorobium Chlorophyll 650 9. Chlorobium Chlorophyll 666

116 to chlorophyll 'a'. Chlorophyll molecules photosynthesis. Succinic acid an have a tadpole like structure. It consists of intermediate of Krebs cycle is activated by Mg-Porphyrin head (Hydrophilic Head) the addition of coenzyme A and it reacts and (Lipophilic tail) Phytol tail. The with a simple amino acid glycine and the Porphyrin head consists of four pyrrol reaction goes on to produce chlorophyll 'a'. rings linked together by C-H bridges. Each Bio synthesis of chlorophyll a requires pyrrole ring comprises of four carbons Mg, Fe, Cu, Zn, Mn, K and nitrogen. The and one nitrogen . Porphyrin ring absence of any one of these minerals leads has several side groups which alter the to chlorosis (Recall what you have studied properties of the pigment. Different side in ‘Mineral Nutrition’). groups are indicative of various types of chlorophyll. The Phytol tail made up of ii. Comparison of Chlorophyll – a with 20 carbon alcohol is attached to carbon other pigments 7 of the Pyrrole ring IV. It has a long 1. Chlorophyll 'b' differs from Chlorophyll 'a' propionic acid ester bond. Long lipophilic in having CHO (aldehyde)group instead tail helps in anchoring chlorophyll to the rd of CH3(Methyl) group at the 3 C atom lamellae (Figure 13.2). in II Pyrrol ring (Figure 13.2). i. Biosynthesis of Chlorophyll 2. Chlorophyll 'c' differs from Chlorophyll Chlorophyll is synthesized from 'a' by lacking phytol tail. intermediates of respiration and

Figure 13.2: Structures of Chlorophyll 'a' and 'b'

117 3. Chlorophyll 'd' differs from Chlorophyll 'a' in having O-CHO Separation of Chloroplast pigments nd group instead of CH-CH2 group at 2 by paper Chromatography method Carbon in the 1st Pyrrol ring. Step 1. Extract chlorophyll pigment 4. Pheophytin resembles Chlorophyll 'a' from the leaves using 80% Acetone. except that it lacks Mg atom. Instead it Step 2. Allow to concentrate by has two H atoms. evaporation. 5. Phycobilins have open tetra pyrrols and Step 3. Apply few drops on one they have neither Mg nor phytol chain. end above 2 cm from the edge of a chromatographic paper. 13.3.2 Carotenoids Step 4. A solvent with mixture of Carotenoids are yellow to orange Petroleum ether and acetone in the pigments, mostly tetraterpens and these ratio of 9:1 is prepared and poured pigments absorb light strongly in the blue into development chamber. to violet region of visible spectrum. These Step 5. Place the strip above the pigments protect chlorophyll from photo- solvent by placing one end of the strip oxidative damage. Hence, they are called as touching the solvent. shield pigments. These pigments absorb light and transfer these to chlorophyll. Observation Almost all carotenoid pigments have After one hour observe the 40 carbon atoms. Ripening of fruits, floral chromatographic paper. You can find colours and leaf colour change during the pigments being separated into autumn is due to Carotenoids (Carotene four distinct spots (Figure 13. 4). and Xanthophyll) (Figure 13.3). Chromatography i. Carotenes: Paper Orange, Red, Yellow and Brownish pigments, hydrocarbons (Lipids) and most Test tube of them are tetraterpenes(C40H56). Carotene Carotenes

Xanthophyll

Chlorophyll a

Chlorophyll b

Ether acetone solvent

Changes in Fruit colour due to Figure 13.3: Paper Chromatography difference in pigmentation Figure 13.4:

118 is the most abundant Carotene in plants and 13.4 Spectrum of Electromagnetic it is a precursor of Vitamin A. Lycopene Radiation is the red pigment found in the fruits of tomato, red peppers and roses. In the total electromagnetic spectrum,visible light is the smallest ii. Xanthophylls: part. The entire life on earth depends

Yellow (C 40H56O2) pigments are like on light and is the driving force for all carotenes but contain oxygen. Lutein is organisms. Plants have natural potential responsible for yellow colour change of to utilize solar energy directly. In the leaves during autumn season. Examples: given picture electromagnetic radiation Lutein, Violaxanthin and Fucoxanthin. spectrum and components of visible spectrum are mentioned. The wavelength 13.3.3 Phycobilins of solar radiation which reaches the earth They are proteinaceous pigments, soluble is between 300 to 2600 nm. The visible in water, and do not contain Mg and spectrum ranges between 390 to 763 nm Phytol tail. They exist in two forms such (3900 å to 7630 å). The colour of the light as 1. Phycocyanin found in cyanobacteria is determined by the wavelength. Energy 2. Phycoerythrin found in rhodophycean of the quantum is inversely proportional algae (Red algae). to wavelength. Shorter wavelength has

Figure 13.5: Electromagnetic Spectrum

119 more energy than longer wavelength. 13.5 Photosynthetic Unit (Quantasome) Electromagnetic spectrum consists of Quantasomes are the morphological 8 types of radiations such as cosmic rays, expression of physiological gamma rays, X rays, U-V rays, Visible photosynthetic units, located on the light spectrum, infrared rays, electric rays inner membrane of thylakoid lamellae. and radio rays (Figure 13. 5). Each quantasome measures about 180 å × 160 å and 100 åthickness. In 1952, Light is extremely Steinman observed granular structures variable and if radiation in chloroplast lamellae under electron is evenly distributed microscope. Later, Park and Biggins over the globe it is (1964) confirmed these granular structures sufficient to melt 35 m thick ice layer. as physiological units of photosynthesis and coined the term Quantasome. Properties of Light According to them one quantasome 1. Light is a transverse electromagnetic contains about 230 chlorophyll molecules. wave. A minimum number of chlorophyll and 2. It consists of oscillating electric and other accessory pigments act together magnetic fields that are perpendicular in a photochemical reaction to release to each other and perpendicular to the one oxygen or to reduce one molecule of direction of propagation of the light. CO2. It constitutes a photosynthetic unit. (Figure 13.7) and (1932) 3. Light moves at a speed of 3 × 108 ms–1 Emerson Arnold based on flashing light experiment found 4. Wavelength is the distance between 2500 chlorophyll molecules are required successive crests of the wave. to fix one molecule of CO2. However, the 5. Light as a particle is called . photon reduction or fixation of one CO2 requires Each photon contains an amount of 10 quanta of light and so each unit would energy known as quantum. contain 1/10 of 2500 i.e. 250 molecules. 6. The energy of a photon depends on the Usually 200 to 300 chlorophyll molecules frequency of the light (Figure 13. 6). are considered as a physiological unit of photosynthesis. According to Emerson 8 quanta of light are required for the release Electric-field of one oxygen molecule or reduction of one Component Carbon dioxide molecule. The quantum yield is 1/8 or 12 %.

Direction of 13.6 Absorption Spectrum and Action Propagation Spectrum Wavelenth (λ) 13.6.1 Absorption Spectrum Magnetic-field component The term absorption refers to complete Figure 13.6: Oscillation of electric and retention of light, without reflection or magnetic vectors in light

120 Chlorophyll a Carotene Thylakoid Chlorophyll b 100

80 Action 60 spectrum

Antenna 40 Molecule 20 Absorption spectrum

Photosynthetic rate / Absorption rate Photosynthetic rate / 0 400 600 700 Chlorophyll b 500 Wavelength (nm) Carotenoid Figure 13. 8: Absorption and action spectrum Figure 13.7: Quantasome spectrum is the absorption maxima for transmission. Pigments absorb different Chlorophyll (a) and Chlorophyll (b). wavelengths of light. A curve obtained The Action Spectrum is instrumental by plotting the amount of absorption of in the discovery of the existence of different wavelengths of light by a pigment two photosystems in O2 evolving is called its absorption spectrum. photosynthesis (Figure 13. 8). • Chlorophyll 'a' and chlorophyll 'b' absorb quanta from blue and red region 13.7 Emerson’s Experiments and Hill’s • Maximum absorption peak for different Reaction forms of chlorophyll 'a' is 670 to 673, 680 to 683 and 695 to 705nm. 13.7.1 Red Drop or Emerson’s First Effect • Chlorophyll 'a' 680 (P680) and Emerson conducted experiment in Chlorophyll 'a' 700 (P700) function as Chlorella using only one wavelength of trap centre for PS II and PS I respectively. light (monochromatic light) at a time and he measured quantum yield. He plotted 13.6.2 Action Spectrum a graph of the quantum yield in terms

The effectiveness of different wavelength of O2 evolution at various wavelengths of of light on photosynthesis is measured light. His focus was to determine at which by plotting against quantum yield. The wavelength the photochemical yield of curve showing the rate of photosynthesis oxygen was maximum. He found that in at different wavelengths of light is the wavelength of 600 to 680 the yield called action spectrum. From the graph was constant but suddenly dropped in the showing action spectrum, it can be region above 680 nm (red region). The fall concluded that maximum photosynthesis in the photosynthetic yield beyond red takes place in blue and red region of region of the spectrum is referred as Red the spectrum. This wavelength of the drop or Emerson’s first effect.

121 13.7.2 Emerson’s Enhancement Effect Conclusions of Hill’s Reaction: Emerson modified 1. During photosynthesis oxygen is his first experiment evolved from water. by supplying shorter 2. Electrons for the reduction of CO2 wavelength of light are obtained from water. (red light) along with 3. Reduced substance produced, later longer wavelength of helps to reduce CO2 light (far red light). He found that the monochromatic light of longer wavelength 2H2O 1 2A 2 AH2 1 O2 (far red light) when supplemented with A is the Hydrogen acceptor, the common in shorter wavelength of light (red light) vitro hydrogen acceptors are ferricyanide, enhanced photosynthetic yield and benzoquinone and Di Chloro Phenol recovered red drop. This enhancement Indole Phenol (DCPIP). of photosynthetic yield is referred to as Emerson’s Enhancement Effect 13.8 Modern Concept of Photosynthesis (Figure 13.9). Photosynthesis is an Oxidation and Reduction process. Water 650 +710 (Red + Far red) 650nm (Red) is oxidised to release O2

710nm (Far red) and CO2 is reduced to form sugars. The first phase requires light and

Rate of Photosynthesis is called light reaction or λ of light exposed (nm) Hill’s reaction. Figure 13.9: Emerson’s Enhancement Effect 1. Light reaction: It is a photochemical Photosynthetic rate at far red light reaction whereas dark reaction is a (710 nm) 5 10 thermochemical reaction. Photosynthetic rate at red light Solar energy is trapped by chlorophyll (650 nm) 5 43.5 and stored in the form of chemical energy Photosynthetic rate at red 1 far red (assimilatory power)as ATP and reducing (650 1 710 nm) 5 72.5 (Enhancement power NADPH 1 H1. NADPH 1 H1 effect). alone are known as reducing powers. This reaction takes place in thylakoid membrane 13.7.3 Hill’s Reaction of the chloroplast. Oxygen is evolved as a R. Hill (1937) isolated chloroplasts result of splitting of water molecules by light. and when they were illuminated in the Light reaction is discussed in two phases: presence of suitable electron acceptors i. Photo-oxidation Phase: such as ferricyanide, they were reduced • Absorption of light energy. to ferrocyanide and oxygen is evolved. • Transfer of energy from accessory Hill’s Reaction is now considered to be pigments to reaction centre. equivalent to Light Reaction. • Activation of Chlorophyll 'a' molecule.

122 ii. Photo Chemical Phase: molecule is in an excited state, this excitation • Photolysis of water and oxygen evolution energy is utilised for the phosphorylation. • Electron transport and synthesis of Phosphorylation takes place with the help assimilatory power. of light generated electron and hence it is known as photophosphorylation. 2. Dark reaction (Biosynthetic phase): Fixation and reduction of CO into 2 13.9.1 Fluorescence and Phosphorescence carbohydrates with the help of assimilatory Normal state of an atom or molecule power produced during light reaction. This is called . When a photon reaction does not require light and is not ground state of light collides with the chlorophyll directly light driven. Hence, it is called as molecule, an electron from outer most Dark reaction or Calvin-Benson cycle orbit is moved to higher energy orbit (Figure 13.10). causing excitation of chlorophyll. This is known as excited state. There are three excited states such as:

1. First singlet state (S1)

2. Second singlet state (S2)

3. First Triplet Sate (T1) When a red light strikes chlorophyll molecule, one electron is released from

its ground level (S0) to first singlet state

(S1). It is in unstable state having half-life period of 10-9 seconds. When a blue light Light and Dark Reaction Figure 13.10: strikes chlorophyll molecule, one electron is released from its ground level (S ) to 13.9 Photo-Oxidation Phase of Light 0 second singlet state (S2). It is because blue Reaction light has shorter wavelength and more The action of photon plays a vital role in energy than red light. This state is also excitation of pigment molecules to release unstable having half-life period of less an electron. When the molecules absorb a –12 than 10 seconds. Both S1 and S2 states photon, it is in excited state. When the light being unstable move to ground state S0 source turned off, the high energy electrons by releasing energy through the several return to their normal low energy orbitals as possible ways. the excited molecule goes back to its original stable condition known as ground state. i. Fluorescence When molecules absorb or emit light they The electron from first singlet state (S1) change their electronic state. Absorption of returns to ground state (S0) by releasing blue light excites the chlorophyll to higher energy in the form of radiation energy energy state than absorption of Red light, (light) in the red region and this is because the energy of photon is higher when known as fluorescence. Fluorescence their wavelength is shorter. When the pigment is the immediate emission of absorbed

123 S –12 2 (Half Life 10 Sec.) of absorbed radiations. Pathway of electron

during Phosphorescence: S2 → S1 → T1 → S0 –9 S1 (Half Life 10 Sec.) 13.9.2 Photosystem and Reaction Centre –3 T1(Half Life 10 Sec.) • Thylakoid membrane contains λ2 λ1 F P

Energy Level Photosystem I (PS I) and Photosystem S 0 II (PS II). Ground State • PS I is in unstacked region of granum Figure 13.11: Fluorescence (F) and facing stroma of chloroplast. Phosphorescence (P) • PS II is found in stacked region of thylakoid radiations (Figure 13.11). Pathway of membrane facing lumen of electron during fluorescence: S → S 1 0 thylakoid. ii. Phosphorescence • Each Photosystem

Electron from Second Singlet State (S2) may consists of central core return to next higher energy level (S1) by complex (CC) and light harvesting losing some of its extra energy in the form Complex (LHC) or Antenna of heat. From first singlet state (S1) electron molecules(Figure 13.12). further drops to first triplet state (T1). Triplet • The core complex consists of respective State is unstable having half life time of 10-3 reaction centre associated with proteins, seconds and electrons returns to ground electron donors and acceptors. state with emission of light in red region • PS I – CC I consists of reaction centre called as (Figure 13.11). phosphorescence P700 and LHC I. Phosphorescence is the delayed emission

Electron transfer Primary electron acceptor Reaction Reaction center center Photon Chlorophyll

Transfer of energy

Antenna pigment molecules Figure 13.12: Photosystem

124 Table 13.2: Differences between Photosystem I and Photosystem II Photosystem I Photosystem II 1. The reaction centre is P700 1. Reaction centre is P680 2. PS I is involved in both cyclic and 2. PS II participates in Non-cyclic non-cyclic. pathway 3. Not involved in photolysis of water and 3, Photolysis of water and evolution of evolution of oxygen oxygen take place. 4. It receives electrons from PS II during 4. It receives electrons by photolysis of non-cyclic photophosphorylation water 5. Located in unstacked region granum 5. Located in stacked region of thylakoid facing chloroplast stroma membrane facing lumen of thylakoid. 6. Chlorophyll and Carotenoid ratio is 6. Chlorophyll and Carotenoid ratio is 20 to 30:1 3 to 7:1

• PS II – CC II consists of reaction centre of water is due to strong oxidant which is P680 and LHC II (Table 13.2). yet unknown and designated as Z or Yz. • Light Harvesting Complex consists of Widely accepted theory proposed by Kok several , carotenoids and et al.,(1970) explaining photo-oxidation of xanthophyll molecules. water is water oxidising clock (or) S’ State • The main function of LHC is to harvest Mechanism. It consists of a series of 5 states called as S , S , S , S and S . Each state light energy and transfer it to their 0 1 2 3 4 respective reaction centre. acquires positive charge by a photon (hv) and after the S4 state it acquires 4 positive charges, four electrons and evolution of 13.10 Photo chemical phase of light oxygen. Two molecules of water go back to reaction 1 - the S0. At the end of photolysis 4 H ,4 e and

In this phase electrons pass through electron O2 are evolved from water (Figure 13.13). carrier molecules and generate assimilatory powers ATP and NADPH 1 H1. Splitting of 2H2 O water molecule generates electrons replacing s O electrons produced by the light. 4 2 + 13.10.1 Photolysis of Water H s The process of Photolysis is associated with 3 s0 (OEC) or water H+ Oxygen Evolving Complex + splitting complex in pigment system II and H + is catalysed by the presence of Mn11 and H – s Cl . When the pigment system II is active 2 s1 it receives light and the water molecule splits into OH– ions and H1 ions. The OH– ions unite to form water molecules again Figure 13.13: Oxygen Evolving and release O2 and electrons. Photolysis Complex (OEC)

125 PQ acts as shuttle between PS II and 1 – 4 H2O 4 H 1 4 OH Cytochrome b6- f complex and PC – – 4 OH 2 H2O 1 O2 1 4 e connects 2H O 4 H1 1 O 1 4 e– 2 2 • Cytochrome b6-f and PS I complex. • ATPase complex or Coupling factor: 13.10.2 Electron Transport Chain of It is found in the surface of thylakoid membrane. Th is complex is made up Chloroplast

Figure 13.14: Electron Transport Chain in Chloroplast

Electron transport chain in each of CF1 and CF0 factors. Th is complex photosystem involves four complexes: utilizes energy from ETC and converts

• Core Complex (CC): CC I in PS I the ADP and inorganic phosphate (Pi) into reaction centre is P700, CC II in PS II ATP (Figure 13.14). the reaction centre is P680 • Light Harvesting Complex or Antenna 13.11 Photophosphorylation complex (LHC): Phosphorylation taking place during • Two types: LHC I in PS I and LHC II respiration is called as oxidative in PS II. phosphorylation and ATP produced • Cytochrome b6 f complex: It is the by the breakdown of substrate is known non-pigmented protein complex as substrate level phosphorylation. connecting PS I and PS II. In this topic, we are going to learn Plastoquinone (PQ) and Plastocyanin about phosphorylation taking place in (PC) are intermediate complexes chloroplast with the help of light. During acting as mobile or shuttle electron the movement of electrons through carrier carriers of Electron Transport Chain. molecules ATP and NADPH 1 H1 are

126 produced. Phosphorylation is the process - ADP+ P 2e FRS of synthesis of ATP by the addition of i ATP Ferredoxin inorganic phosphate to ADP. The addition 2e- Light of phosphate here takes place with the Cyt b6 - - 2e help of light generated electron and so 2e it is called as . It ADP+ P photophosphorylation i Cyt f takes place in both cyclic and non-cyclic 2e- - P700 electron transport. ATP PC 2e PS I LHC I 13.11.1 Cyclic Photophosphorylation Cyclic photophosphorylation refers to Figure 13.15: Cyclic Photophosphorylation the electrons ejected from the pigment system I (Photosystem I) and again cycled 13.11.2 Non-Cyclic Photophosphorylation back to the PS I. When the photons When photons are activated reaction activate P700 reaction centre photosystem centre of pigment system II(P680), II is activated. Electrons are raised to electrons are moved to the high energy the high energy level. The primary level. Electrons from high energy electron acceptor is Ferredoxin Reducing state passes through series of electron Substance (FRS) which transfers electrons carriers like pheophytin, plastoquinone, to Ferredoxin (Fd), Plastoquinone (PQ), cytochrome complex, plastocyanin and cytochrome b6-f complex, Plastocyanin finally accepted by PS I (P700). During (PC) and finally back to chlorophyll this movement of electrons from PS II to P700 (PS I). During this movement PS I ATP is generated (Figure 13. 16). PS I of electrons Adenosine Di Phosphate (P700) is activated by light, electrons are (ADP) is phosphorylated, by the addition moved to high energy state and accepted of inorganic phosphate and generates by electron acceptor molecule ferredoxin Adenosine Tri Phosphate (ATP). Cyclic reducing Substance (FRS). During the electron transport produces only ATP and downhill movement through ferredoxin, there is no NADPH 1 H1 formation. At electrons are transferred to NADP1 and each step of electron transport, electron reduced into NADPH 1 H1 (H1 formed loses potential energy and is used by from splitting of water by light). the transport chain to pump H1 ions Electrons released from the across the thylakoid membrane. The photosystem II are not cycled back. It proton gradient triggers ATP formation is used for the reduction of NADP1 in in ATP synthase enzyme situated on the to NADPH 1 H1. During the electron thylakoid membrane. Photosystem I need transport it generates ATP and hence this light of longer wave length (> P700 nm). type of photophosphorylation is called It operates under low light intensity, less non-cyclic photophosphorylation. The

CO2 and under anaerobic conditions electron flow looks like the appearance which makes it considered as earlier in of letter ‘Z’ and so known as Z scheme. evolution (Figure 13.15). When there is availability of NADP1 for reduction and when there is splitting of

127 -2.0 - FRS 4e

- Q 4e Ferredoxin -1.0 Pheophytin Light - - - 4e PQ 4e 4e + + 2NADP 2NADPH+H - Cyt b6,f 0 Light 4e - complex 4e P700 ADP+ Pi PC - PS I +1.0 P680 4e ATP LHC I

PS II - 2H O LHC II 4e 2 ++ ++ Mn , Ca ,Cl - O Evolving O2 + 2 4H Complex

Figure 13.16: Non-Cyclic Photophosphorylation water molecules both PS I and PS II are 13.11.3 Bio energetics of light reaction activated (Table 13.3). Non-cyclic electron • To release one electron from pigment transport PS I and PS II both are involved system it requires two quanta of light. co-operatively to transport electrons from • One quantum is used for transport of water to NADP1 (Figure 13.6). In oxygenic electron from water to PS I. species non-cyclic electron transport takes place in three stages. • Second quantum is used for transport of electron from PS I to NADP1 i. Electron transport from water to P680: • Two electrons are required to generate Splitting of water molecule produce one NADPH 1 H1. electrons, protons and oxygen. Electrons • During Non-Cyclic electron transport lost by the PS II (P680) are replaced by two NADPH 1 H1 are produced and it electrons from splitting of water molecule. requires 4 electrons. ii. Electron transport from P680 to P700: • Transportation of 4 electrons requires Electron flow starts from P680 through 8 quanta of light. a series of electron carrier molecules like pheophytin, plastoquinone (PQ), Check your grasp! cytochrome b -f complex, plastocyanin 6 Name the products produced from (PC) and finally reaches P700 (PS I). Non-Cyclic photophosphorylation? 1 iii. Electron transport from P700 to NADP Why does PS II require electrons from PS I(P700) is excited now and the electrons water? pass to high energy level. When electron Can you find the difference in the travels downhill through ferredoxin, Pathway of electrons during PS I and 1 1 NADP is reduced to NADPH 1 H . PS II?

128 Table 13.3 Differences between Cyclic Photophosphorylation and Non-Cyclic Photophosphorylation Cyclic Photophosphorylation Non-Cyclic Photophosphorylation 1. PS I only involved 1. PS I and PS II involved 2. Reaction centre is P700 2. Reaction centre is P680 3. Electrons released are cycled back 3. Electron released are not cycled back 4. Photolysis of water does not take place 4. Photolysis of water takes place 5. Only ATP synthesized 5. ATP and NADPH 1 H1are synthesized 6. Phosphorylation takes place at two 6. Phosphorylation takes place at only one places place 7. It does not require an external electron 7. Requires external electron donor like

donor H2O or H2S 8. It is not sensitive to di chloro di methyl 8. It is sensitive to DCMI and inhibits urea (DCMI) electron flow

13.12 Chemiosmotic Theory H+ Chemiosmosis theory was proposed by NADP+ + Cytochromes NADPH+H P. Mitchell (1966). According to this b & f PS PS II I theory electrons are transported along MEN LU H+ the membrane through PS I and PS II and + H H+ Thylakoid H+ membrane connected by Cytochrome b6-f complex. The + + H flow of electrical current is due to difference H in electrochemical potential of protons across STROMA the membrane. Splitting of water molecule ADP ATP ATP Synthase takes place inside the membrane. Protons Chemiosmotic Theory or H1 ions accumulate within the lumen Figure 13.17: of the thylakoid (H1 increase 1000 to 2000 membrane stimulates ATP generation times). As a result, proton concentration (Figure 13.17). is increased inside the thylakoid lumen. The evolution of one oxygen molecule These protons move across the membrane (4 electrons required) requires 8 quanta because the primary acceptor of electron is of light. C3 plants utilise 3 ATPs and located outside the membrane. Protons in 2 NADPH 1 H1 to evolve one Oxygen stroma less in number and creates a proton molecule. To evolve 6 molecules of gradient. This gradient is broken down Oxygen 18 ATPs and 12 NADPH 1 H1 due to the movement of proton across the are utilised. C4 plants utilise 5 ATPs and 1 membrane to the stroma through CFO of the 2 NADPH 1 H to evolve one oxygen ATP synthase enzyme. The proton motive molecule. To evolve 6 molecules of force created inside the lumen of thylakoid Oxygen 30 ATPs and 12 NADPH 1 H1 or chemical gradient of H1 ion across the are utilised.

129 dioxide into carbohydrates. This reaction Check your grasp! does not require light. Therefore, it is named What will be the quanta requirement Dark reaction. Ribulose 1,5 bisphosphate for complete light reaction which (RUBP) act as acceptor molecule of carbon

releases 6 oxygen molecules? dioxide and fix the CO2 by RUBISCO Solution: Complete light reaction enzyme. The first product of the pathway is releases 6 oxygen molecules. If a 3- carbon compound (Phospho Glyceric

one molecule of oxygen evolution Acid) and so it is also called as C3 Cycle. It requires 8 quanta means, for 6 oxygen takes place in the stroma of the chloroplast. molecules 6 × 8 5 48 quanta of light M. Melvin Calvin, A.A. Benson and their required for complete light reaction. co-workers in the year 1957 found this path way of carbon fixation. Melvin Calvin was 13.13 Dark Reaction or C3 Cycle or awarded Nobel Prize for this in 1961 and this pathway named after the discoverers Biosynthetic Phase or Photosynthetic as Calvin-Benson Cycle. Dark reaction Carbon Reduction (PCR)Cycle is temperature dependent and so it is also Biosynthetic phase of photosynthesis called thermo-chemical reaction. utilises assimilatory powers(ATP and Dark reaction consists of three phases: NADPH 1 H1) produced during light (Figure 13.18). reaction are used to fix and reduce carbon

Figure 13.18: Phases of Calvin Cycle

130 phosphate pool phosphate

3C t hexose Stromal r o 3C p x E G3P 6C (DHAP) Acetone Phoshate Dihydroxy i 6C P G3P Starch Fructose 1,6 Bis Phosphate DHAP G3P Aldolase Fructose 6 Phosphate Glucose 1 Phosphate Glucose 6 Phosphate Phosphatase G3P G3P DHAP Glyceraldehyde 3 -Phosphate (G3P) pool Xylulose G3P 5 Phosphate 5C 7C i + i P Calvin cycle Aldolase Phosphatase Erythrose 6 NADP 4 Phosphate 4C 6 ADP+ 6 P 7 Phosphate Sedoheptulose Kinase Figure 13.19: Figure Dehydrogenase 6 ATP 6 NADPH Sedoheptulose 1,7 Bis Phosphate 7C 5C 3C Epimerase Glycerate 3-Phospho Ribose (6) 5-Phosphate Xylulose O ADP 2 C 5 Phosphate 3 5C S 3 ATP I B Isomerase

(3)CO U R Epimerase Kinase Ribulose Ribulose (3) 5C (3) 5-Phosphate 5C 1,5-Bis Phosphate

131 1. Carboxylation (fixation) requires 3 ATPs and 2 NADPH 1 H1, and

2. Reduction (Glycolytic Reversal) for the fixation of 6 CO2 requires 18 ATPs and 12 NADPH 1 H1 during C cycle. One 3. Regeneration 3 6 carbon compound is the net gain to form Phase 1- Carboxylation (Fixation) hexose sugar. The acceptor molecule Ribulose 1,5 ATP ADP Bisphosphate (RUBP) a 5 carbon compound RU5P RUBP with the help of RUBP carboxylase oxygenase (RUBISCO) enzyme accepts Overall equation for dark reaction: one molecule of carbon dioxide to form 6CO 1 18ATP 1 12NADPH 1 H1 an unstable 6 carbon compound. This 2 C H O 1 6H O1 18ADP 1 18Pi 1 6C compound is broken down into two 6 12 6 2 molecules of 3-carbon compound phospho 12NADP1 glyceric acid (PGA) (Figure 13.19). Rubisco RUBP 1 CO 2 molecules PGA RUBISCO – RUBP 2 Carboxylase Oxygenase enzyme, Phase 2 – Glycolytic Reversal / is the most abundant Reduction protein found on earth. It constitutes Phospho glyceric acid is phosphorylated 16 % of the chloroplast protein. It acts by ATP and produces 1,3 bis phospho as carboxylase in the presence of CO2 glyceric acid by PGA kinase. 1,3 bis phospho and oxygenase in the absence of CO2. glyceric acid is reduced to glyceraldehyde 3 Phosphate (G-3-P) by using the reducing 13.14 Hatch & Slack Pathway or C4 power NADPH 1 H1. Glyceraldehyde Cycle or Dicarboxylic Acid 3 phosphate is converted into its isomeric Pathway or Dicarboxylation form di hydroxy acetone phosphate (DHAP). Pathway Till 1965, Calvin cycle is the only pathway for PGA PGA Kinase 1,3 bisphosphoglyceric acid ATP ADP CO2 fixation. But in 1965,Kortschak , Hart and Burr made observations in sugarcane and found C or dicarboxylic acid pathway. 4 NADPH 1 H1 NADP1 Malate and aspartate are the major labelled 1,3 bisphosphoglceric acid products. This observation was confirmed Glyceraldehyde-3-Phosphate by Hatch & Slack in 1967. This alternate

pathway for the fixation of CO2 was found in Phase 3 – Regeneration several tropical and sub-tropical grasses and

Regeneration of RUBP involves the formation some dicots. C4 cycle is discovered in more of several intermediate compounds of than 1000 species. Among them 300 species 6-carbon, 5-carbon,4-carbon and 7- carbon belong to dicots and rest of them are skeleton. Fixation of one carbon dioxide monocots. C4 plants represent about 5% of

132 The C4 pathway Photosynthetic cells of C Mesophyll 4 CO2 plant leaf cell PEP carboxylase

C4 leaf anatomy Oxaloacetate (4c) PEP (3c) Mesophyll cell ADP Malate (4c) ATP Bundle- sheath cell Bundle Pyruvate (3c) sheath CO2 vein cell (vascular calvin tissue) cycle

Sugar

stoma Vascular tissue

Figure 13.20: C4 Cycle

Earth’s plant biomass and 1% of its known require 5 ATP and 2 NADPH 1 H1 to fix plant species. Despite this scarcity, they one molecule of CO2. account for about 30% of terrestrial carbon 13.14.1 Stage: I Mesophyll Cells fixation. Increasing the proportion of C4 plants on earth could assist biosequestration Phosphoenol Pyruvate 1 CO of CO2 and represent an important climate 2 change avoidance strategy. (PEP) (3C) PEP carboxylase

C4 pathway is completed in two phases, first phase takes place in stroma of Oxaloacetic acid (OAA) (4C) mesophyll cells, where the CO2 acceptor molecule is 3-Carbon compound, phospho Oxaloacetic acid (OAA) is converted enol pyruvate (PEP) to form 4-carbon Oxalo into malic acid or aspartic acid and is acetic acid (OAA). The first product is a transported to the bundle sheath cells through plasmodesmata. 4-carbon and so it is named as C4 cycle. oxalo acetic acid is a dicarboxylic acid and hence 13.14.2 Stage: II Bundle Sheath Cells this cycle is also known as dicarboxylic acid pathway (Figure 13.20). Carbon Malic acid undergoes decarboxylation dioxide fixation takes place in two places and produces a 3 carbon compound one in mesophyll and another in bundle Pyruvic acid and CO2. The released CO2 sheath cell (di carboxylation pathway). It is combines with RUBP and follows the the of tropical and sub tropical calvin cycle and finally sugar is released plants growing in warm and dry conditions. to the phloem. Pyruvic acid is transported

Fixation of CO2 with minimal loss is due to the mesophyll cells. to absence of photorespiration. C4 plants

133 Rubisco It RUBP 1 CO 2 PGA Kranz Anatomy: 2 is the German term (5C) (3C) meaning a halo or wreath. In C4 plants Activity vascular bundles are surrounded by a layer of bundle sheath. Bundle sheath is • Collect the leaves of Paddy (C3) and Sugar cane (C ). surrounded by a ring of mesophyll cells. 4 The characteristic feature of C plants is • Take the cross section. 4 the presence of dimorphic chloroplast: • Observe the sections under the Larger microscope. Bundle sheath chloroplast: chloroplast, thylakoids not arranged • See the difference in their anatomy in granum and rich in starch. (Dimorphic chloroplast and Kranz Smaller anatomy). Mesophyll Chloroplast: chloroplast, thylakoids arranged in granum and less starch.

Table 13.4: Differences between C3 and C4 plants

C3 Plants C4 Plants

1. CO2 fixation takes place in mesophyll 1. CO2 fixation takes place mesophyll and cells only bundle sheath

2. CO2 acceptor is RUBP only 2. PEP in mesophyll and RUBP in bundle sheath cells 3. First product is 3C- PGA 3. First product is 4C- OAA 4. Kranz anatomy is not present 4. Kranz anatomy is present 5. Granum is present in mesophyll cells 5. Granum present in mesophyll cells and absent in bundle sheath 6. Normal Chloroplast 6. Dimorphic chloroplast 7. Optimum temperature 20o to 25oC 7. Optimum temperature 30o to 45oC

8. Fixation of CO2 at 50 ppm 8. Fixation of CO2 even less than 10 ppm 9. Less efficient due to higher 9. More efficient due to less photorespiration photorespiration 10. RUBP carboxylase enzyme used for 10. PEP carboxylase and RUBP fixation carboxylase used 11. 18 ATPs used to synthesize one 11. Consumes 30 ATPs to produce one glucose glucose.

12. Efficient at low CO2 12. Efficient at higher CO2

13. Example: Paddy, Wheat, Potato and 13. Example: Sugar cane, Maize, Sorghum, so on Amaranthus and so on

134 4. Due to absence of photorespiration, Check your grasp! CO2 Compensation Point for C4 is C plants requires 30 ATPs and 4 lower than that of C3 plants. 12 NADPH 1 H1 to synthesize one Differences between 3C Plants (C3 Cycle) and glucose, but C3 plants requires only C4 Plants (C4 Cycle) are given in table 13.4. 18 ATPs and 12 NADPH 1 H1 to synthesize one glucose molecule. If 13.15 Crassulacean Acid then, how can you say C4 plants are more advantageous? Metabolism or CAM cycle It is one of the carbon pathways identified Solution: C4 plants are more advantageous in succulent plants growing in semi-arid than C3 plants because most of the energy or xerophytic condition. This was first lost during photo respiration in C3 plants. observed in crassulaceae family plants like

13.14.3 Significance of C4 cycle Bryophyllum, Sedum, Kalanchoe and is the reason behind the name of this cycle. It is 1. Plants having C4 cycle are mainly of tropical and sub-tropical regions and also noticed in plants from other families are able to survive in environment Examples: Agave, Opuntia, Pineapple and Orchids. The stomata are closed during day with low CO2 concentration. and are open during night (Scotoactive). 2. C4 plants are partially adapted to drought conditions. This reverse stomatal rhythm helps to conserve water loss through transpiration 3. Oxygen has no inhibitory effect on and will stop the fixation of CO2 during the C4 cycle since PEP carboxylase is day time. At night time CAM plants fix CO2 insensitive to O2.

Night: Open stomata Day: Closed stomata Open stoma permits Decarboxylation of stored CO2 uptake Closed stoma Atmospheric entry of CO2 and malate and refixation of and fixation prevents H2O loss CO loss of H2O internal CO2 deacidification and CO2 uptake leaf acidification 2

NADP+ malk PEP carboxylase enzyme CO2 Malate Phosphoenol- Oxaloacetate Malic acid NAD+ malic pyruvate NADH dehydro Pyruvate NAD+ Calvin genase cycle Triose Vacuole phosphate Malate Starch

Starch Malic acid Chloroplast Chloroplast Vacuole

Figure 13.21: CAM cycle

135 with the help of Phospho Enol Pyruvic acid their photosynthesis. (PEP) and produce oxalo acetic acid (OAA). 3. Stomata are closed during the day Subsequently OAA is converted into malic time and help the plants to avoid acid like C4 cycle and gets accumulated in transpiration and water loss. vacuole increasing the acidity. During the day time stomata are closed and malic acid 13.16 Photorespiration or C2 Cycle is decarboxylated into pyruvic acid resulting or Photosynthetic Carbon in the decrease of acidity. CO2 thus formed enters into Calvin Cycle and produces Oxidation (PCO) Cycle carbohydrates (Figure13.21). Respiration is a continuous process for all living organisms including plants. Significance of CAM Cycle Decker (1959) observed that rate of respiration is 1. It is advantageous for succulent plants more in light than in dark. Photorespiration to obtain CO from malic acid when 2 is the excess respiration taking place in stomata are closed. photosynthetic cells due to absence of 2. During day time stomata are closed CO2 and increase of O2(Table 13.5). This and CO2 is not taken but continue

(2) O 5C 2

(2) Ribulose 1,5 (2) PGA bis phosphate 2C

Calvin (2) Phospho Glycolate Cycle

3C PGA ADP (2) Pi 3C 2C ATP Glycerate (2) Glycolate

3C P 2C E Glycerate R NAD+ (2) Glycolate O 3C + + O X NADH+H 2 2C HO I

Hydroxy pyruvate 22 S

(2) Glyoxylate O 3C M H22 O + ½ O 2C

Serine (2) Glycine E

3C 2C M IT Serine (2) Glycine O C

H

CO2 O

N

NH3 D

+ + R

NADH+H I

NAD O N

Figure 13.22: Photorespiration

136 condition changes the carboxylase role conditions 50% of the photosynthetic of RUBISCO into oxygenase. C2 Cycle potential is lost because of Photorespiration takes place in chloroplast, peroxisome and (Figure 13.22). mitochondria. RUBP is converted into PGA and a 2C-compound phosphoglycolate by 13.16.1 Significance of photorespiration Rubisco enzyme in chloroplast. Since the 1. Glycine and Serine synthesised during first product is a 2C-compound, this cycle this process are precursors of many is known as . Phosphoglycolate biomolecules like chlorophyll, proteins, C2 Cycle by loss of phosphate becomes glycolate. nucleotides. Glycolate formed in chloroplast enters into 2. It consumes excess NADH 1 H 1 generated. peroxisome to form glyoxylate and hydrogen 3. Glycolate protects cells from Photo peroxide. Glyoxylate is converted into oxidation. glycine and transferred into mitochondria. In mitochondria, two molecules of glycine 13.16.2 Carbon Dioxide Compensation Point combine to form serine. Serine enters into When the rate of photosynthesis equals peroxisome to form hydroxy pyruvate. the rate of respiration, there is no exchange Hydroxy pyruvate with help of NADH 1 H1 of oxygen and carbon dioxide and this is becomes glyceric acid. Glyceric acid is cycled called as carbon dioxide compensation back to chloroplast utilising ATP and point. This will happen at particular light becomes Phosphoglyceric acid (PGA) and intensity when exchange of gases becomes enters into the Calvin cycle (PCR cycle). zero. When light is not a limiting factor and

Photorespiration does not yield any free atmospheric CO2 concentration is between energy in the form of ATP. Under certain 50 to 100 ppm the net exchange is zero.

Table 13.5: Differences between Photorespiration and Dark Respiration Photorespiration Dark respiration 1. It takes place in photosynthetic green 1. It takes place in all living cells cells 2. It takes place only in the presence of 2. It takes place all the time light 3. It involves chloroplast, peroxisome 3. It involves only mitochondria and mitochondria 4. It does not involve Glycolysis, Kreb’s 4. It involves glycolysis, Kreb’s Cycle and Cycle, and ETS ETS 5. Substrate is carbohydrates, protein or 5. Substrate is glycolic acid fats 6. It is not essential for survival 6. Essential for survival 7. Phosphorylation produces ATP 7. No phosphorylation and yield of ATP energy 1 1 8. NADH2 is oxidised to NAD 8. NAD is reduced to NADH2 9. Hydrogen peroxide is produced 9. Hydrogen peroxide is not produced

10. End products are CO2 and PGA 10. End products are CO2 and water

137 13.17 Factors affecting Photosynthesis HIGH LIGHT D INTENSITY E In 1860, Sachs gave three cardinal points theory explaining minimum, optimum MEDIUM LIGHT and maximum factors that control C INTENSITY F photosynthesis. In 1905, Blackman put forth the importance of smallest factor. LOW LIGHT B INTENSITY Blackman’s law of limiting factor is actually a modified Law proposed by Liebig’s Law of minimum. According to A Blackman, OF PHOTOSYNTHESIS RATE “When a process is conditioned CO2 CONCENTRATION as to its rapidity by a number of separate Figure 13.23: Blackman’s Law of Limiting factors, the rate of the process is limited by Factors the pace of the lowest factor”. To conclude in an easy way “at any given point of time the lowest factor among essentials will limit directly controlled by light. Stomatal For example, the rate of photosynthesis”. movement leading to diffusion of CO2 is when even sufficient light intensity is indirectly controlled by light. available, photosynthesis may be low a. Intensity of Light: due to low CO2 in the atmosphere. Here, Intensity of light plays a direct role in CO2 acts as a limiting factor. If CO2 is increased in the atmosphere the rate of the rate of photosynthesis. Under low photosynthesis also increases. Further intensity the photosynthetic rate is low increase in photosynthesis is possible and at higher intensity photosynthetic rate only if the available light intensity is also is higher. It also depends on the nature of increased proportionately (Figure 13.23). plants. Heliophytes (Bean Plant) require Factors affecting photosynthesis higher intensity than Sciophytes (Oxalis). are further grouped into External or b. Quantity of Light: Environmental factors and Internal factors. In plants which are exposed to light I. External factors: Light, carbon for longer duration (Long day Plants) dioxide, temperature, water, mineral photosynthetic rate is higher. and pollutants. c. Quality of light: II. Internal factors: Pigments, protoplasmic factor, accumulation of carbohydrates, Different wavelengths of light affect the rate of anatomy of leaf and hormones. photosynthesis because pigment system does not absorb all the rays equally. Photosynthetic 13.17.1. External factors rate is maximum in blue and red light. Photosynthetically Active Radiation (PAR) 1. Light is between 400 to 700 nm. Red light induces Energy for photosynthesis comes only highest rate of photosynthesis and green light from light. Photooxidation of water and induces lowest rate of photosynthesis. excitation of pigment molecules are

138 2. Carbon dioxide 5. Water

CO2 is found only 0.3 % in the atmosphere Photolysis of water provides electrons and but plays a vital role. Increase in protons for the reduction of NADP, directly. concentration of CO2 increases the rate of Indirect roles are stomatal movement and photosynthesis (CO2 concentration in the hydration of protoplasm. During water atmosphere is 330 ppm). If concentration stress, supply of NADPH 1 H1 is affected. is increased beyond 500ppm, rate of photosynthesis will be affected showing the 6. Minerals inhibitory effect. Deficiency of certain minerals affect photosynthesis e.g. mineral involved in the 3. Oxygen synthesis of chlorophyll (Mg, Fe and N), The rate of photosynthesis decreases Phosphorylation reactions (P), Photolysis when there is an increase of oxygen of water (Mn and Cl), formation of concentration. This Inhibitory effect of plastocyanin (Cu). oxygen was first discovered by Warburg (1920) using green algae Chlorella. 7. Air pollutants

Pollutants like SO2, NO2, O3 (Ozone) and 4. Temperature Smog affects rate of photosynthesis. The optimum temperature for photosynthesis varies from plant to plant. Temperature is 13.17.2 Internal Factors not uniform in all places. In general, the optimum temperature for photosynthesis 1. Photosynthetic Pigments is 25oC to 35oC. This is not applicable for It is an essential factor and even a all plants. The ideal temperature for plants small quantity is enough to carry out o o photosynthesis. like Opuntia is 55 C, Lichens 20 C and Algae growing in hot spring photosynthesis 2. Protoplasmic factor is 75oC. Whether high temperature or low Hydrated protoplasm is essential for temperature it will close the stomata as well photosynthesis. It also includes enzymes as inactivate the enzymes responsible for responsible for Photosynthesis. photosynthesis (Figure 13. 24). Rate of Photosynthesis Rate of Photosynthesis Rate of Photosynthesis

Light intensity CO2 Concentration Temperature Figure 13.24: Factors affecting Photosynthesis

139 3. Accumulation of Carbohydrates Experiment to determine rate Photosynthetic end products like of photosynthesis by Wilmott’s carbohydrates are accumulated in cells bubbler and if translocation of carbohydrates Wilmott’s bubbler consists of a wide is slow then this will affect the rate of mouth bottle fitted with single holed photosynthesis. cork, a glass tube with lower end having 4. Anatomy of leaf wider opening to insert plant, Hydrilla Thickness of cuticle and epidermis, the upper end fitted to a narrow bottle distribution of stomata, presence or absence with water (Figure 13.25). of Kranz anatomy and relative proportion of photosynthetic cells affect photosynthesis.

5. Hormones Water Hormones like gibberellins and cytokinin increase the rate of photosynthesis.

Test tube funnel experiment or Experiment to prove oxygen evolved during Photosynthesis

1. Place Hydrilla plant at the bottom of a beaker containing water. Specimen tube 2. Cover the plant with an inverted funnel. Hydrilla 3. Invert a test tube over the funnel. 4. Keep this setup in sunlight. Figure 13.25: Wilmott’s Bubbler Note your observations (Figure 13. 26).

1. Fill the bottle with water and Gas collected by downward displacement of water insert Hydrilla twig into the wider part of the tube Test tube 2. Hydrilla plant should be cut inside the water to avoid entry of air

bubbles Poond water 3. Fix the tube with jar which acts as water reservoir Inverted funnel

4. Keep the apparatus in sunlight Hyydrilla 5. Count the bubbles when they are in same size. Figure 13.26: Test tube funnel experiment

140 Table 13.6: Difference between photosynthesis in plants and photosynthesis in bacteria Photosynthesis in Plants Photosynthesis in Bacteria 1. Cyclic and non-cyclic phosphorylation 1. Only cyclic phosphorylation takes takes place place 2. Photosystem I and II involved 2. Photosystem I only involved

3. Electron donor is water 3. Electron donor is H2S 4. Oxygen is evolved 4. Oxygen is not evolved

5. Reaction centres are P700 and P680 5. Reaction centre is P870 6. Reducing agent is NADPH 1 H1 6. Reducing agent is NADH 1 H1 7. PAR is 400 to 700 nm 7. PAR is above 700 nm 8. Chlorophyll, carotenoid and 8. Bacterio chlorophyll and bacterio xanthophyll viridin 9. Photosynthetic apparatus – chloroplast 9. It is chlorosomes and chromatophores

13.18 Photosynthesis in bacteria Summary Though we study about bacterial Photosynthesis is an oxidation and reduction photosynthesis as the last part, bacterial process. It has two phases: the light reaction and photosynthesis formed first and foremost dark reaction. During light reaction water is in evolution. Bacteria does not have oxidised to release O2 and during dark reaction specialized structures like chloroplast. CO2is reduced to form sugars. Solar energy It has a simple type of photosynthetic is trapped by pigment system I and pigment apparatus called chlorosomes and system II. P700 and P680 act as reaction centres chromatophores (Table 13.6). Van Neil for PS I and PS II respectively. Splitting of water (1930) discovered a bacterium that molecule (Photolysis) produces electrons, releases sulphur instead of oxygen during protons and oxygen. Photophosphorylation photosynthesis. Here, electron donor is takes place through cyclic and non-cyclic mechanisms and generates energy and reducing hydrogen sulphide (H2S) and only one photosystem is involved (PS I) and the power. Dark reaction or biosynthetic phase of photosynthesis use the products of light energy reaction centre is P870. Pigments present in bacteria are bacteriochlorophyll a, b, c, (ATP and NADPH 1 H1) and carbon dioxide d, e and g and carotenoids. Photosynthetic is reduced to Carbohydrates. Carbon pathway bacteria are classified into three groups: in C3 cycle has RUBP as the acceptor molecule and the first product is PGA (3C). Carbon 1. Green sulphur bacteria. Example: pathway in C4 plants involves mesophyll Chlorobacterium and Chlorobium. and bundle sheath cells, Kranz anatomy. 2. Purple sulphur bacteria. Example: Dimorphic chloroplast, no photorespiration, Thiospirillum and Chromatium. acceptor molecule as PEP and first product as 3. Purple non-sulphur bacteria. Example: OAA (4C) are some of the unique characters of C cycle. C Cycle or photorespiration is Rhodopseudomonas and Rhodospirillum. 4 2 operated when less amount of CO2 is used for

reduction and O2 increases. Rubisco starts to

141 play oxygenase role. Succulent and xerophytic a. 2ATP 1 2NADPH plants show reverse stomatal rhythm as they b. 2ATP 1 3NADPH open during night time and close during c. 3ATP 1 2NADPH day time and follow CAM cycle. Night time d. 3ATP 1 3NADPH produces malic acid and during day time malate is converted into pyruvate and produces 5. Identify true statement regarding light reaction of photosynthesis? CO2 which is reduced to carbohydrates. Photosynthesis is affected by internal and a. Splitting of water molecule is associate external factors. Bacterial photosynthesis is the with PS I. primitive type of photosynthesis and it involves b. PS I and PS II involved in the only photosystem I. formation of NDPH1H1. Evaluation c. The reaction center of PS I is 1. Assertion (A): Chlorophyll a with absorption peak Increase in Proton at 680 nm. gradient inside lumen d. The reaction center of PS II is responsible for ATP Chlorophyll a with absorption peak synthesis at 700 nm. Reason (R): Oxygen evolving complex 6. Two groups (A & B) of bean plants of of PS I located on thylakoid membrane similar size and same leaf area were placed facing Stroma, releases H1 ions in identical conditions. Group A was a. Both Assertion and Reason are True. exposed to light of wavelength 400-450nm & Group B to light of wavelength of 500- b. Assertion is True and Reason is False. 550nm. Compare the photosynthetic rate c. Reason is True and Assertion is False. of the 2 groups giving reasons. d. Both Assertion and Reason are False. 7. A tree is believed to be releasing oxygen 2. Which chlorophyll molecule does not during night time. Do you believe the have a phytol tail? truthfulness of this statement? Justify a. Chl- a b. Chl-b c. Chl- c d. Chl -d your answer by giving reasons? 3. The correct sequence of flow of electrons 8. Grasses have an adaptive mechanism in the light reaction is to compensate photorespiratory losses- a. PS II, plastoquinone, cytochrome, PS Name and describe the mechanism. I, ferredoxin. 9. In Botany class, teacher explains, Synthesis of one glucose requires 30 ATPs in C b. PS I, plastoquinone, cytochrome, PS 4 plants and only 18 ATPs in C plants. The II ferredoxin. 3 same teacher explains C plants are more c. PS II, ferredoxin, plastoquinone, 4 advantageous than C3 plants. Can you cytochrome, PS I. identify the reason for this contradiction? d. PS I, plastoquinone, cytochrome, PS 10. When there is plenty of light and higher II, ferredoxin. concentration of O2, what kind of

4. For every CO2 molecule entering the C3 pathway does the plant undergo?Analyse cycle, the number of ATP & NADPH the reasons. required 142 t ICT Corner Photosynthesis

Let’s play photosynthesis

Steps • Scan the QR code • Start a new game and tap • Click light dependent reaction and follow the steps • After completion – move back and Click Calvin cycle reaction and follow the steps

Activity • Observe the cycle and record it • Check your grasp by click the Quiz tap • Conclude your observations.

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143 Chapter 14 Respiration

Plant and Animal Interdependence Learning Objectives In , plants and animals The learner will be able to, are complementary systems which • Recognize the stages of glucose are integrated to sustain life. In breakdown and its redox system. plants, oxygen enters through the • Differentiate aerobic respiration stomata and it is transported to from anaerobic respiration. cells, where oxygen is utilized for • Describe the conditions under energy production. Plants require which respiration occurs. carbon dioxide to survive, to produce • Realize the role of mitochondria as carbohydrates and to release oxygen power house of the cell. through photosynthesis. These oxygen molecules are inhaled by human • Understand, how ATP molecules through the nose, which reaches the are generated during respiration. where oxygen is transported through the and it reaches cells. Chapter Outline Cellular respiration takes place inside the cell. A specialized respiratory 14.1 Gaseous exchange system is present in animals but Structure of ATP 14.2 is absent in plants for delivering 14.3 Redox reactions oxygen inside the cell. But the cellular 14.4 Types of Respiration respiration stages are similar in both 14.5 Stages of Respiration plants and animals which hint at evolutionary divergence. 14.6 Respiratory Quotient 14.7 Anaerobic Respiration

14.8 Factors Affecting Respiration O2 14.9 Pentose Phosphate Pathway CO2

144 If you are sleeping under a tree organic substances which are oxidised during night time you will feel difficulty during respiration are called respiratory in breathing. During night, plants take substrates. Among these, glucose is up oxygen and release carbon dioxide the commonest respiratory substrate. and as a result carbon dioxide will be Breaking of C-C bonds of complex organic abundant around the tree. This process compounds through oxidation within the of CO2 evolution is called respiration. cells leads to energy release. The energy This process takes place during day time released during respiration is stored in the also (Figure 14.1). It is accompanied by form of ATP (Adenosine Tri Phosphate) as breakdown of substrates and release of well as liberated heat. Respiration occurs energy. In this chapter, respiration process in all the living cells of organisms. The in plants at cellular level will be dealt with. overall process of respiration corresponds to a reversal of photosynthesis.

C6H12O6 1 6O2 → 6CO2 1 6H2O 1 Energy (686 K cal or 2868 KJ) COO 2 2 O

O 2 Depending upon the nature of 2 CO respiratory substrate, Blackman divided respiration into, 1. Floating respiration 2. Protoplasmic respiration When carbohydrate or fat or organic acid serves as respiratory substrate and it is

2 called floating respiration. It is a common O CO 2 mode of respiration and does not produce any toxic product. Whereas respiration utilizing protein as a respiratory substrate, it is called protoplasmic respiration. Protoplasmic respiration is rare and it depletes structural and functional Figure 14.1: Gaseous exchange in plants proteins of protoplasm and liberates toxic ammonia. 14.1 Gaseous Exchange 14.1.2 Compensation point 14.1.1 Respiration At dawn and dusk the intensity of light The term respiration was coined by is low. The point at which CO2 released Pepys (1966). Respiration is a biological in respiration is exactly compensated by process in which oxidation of various CO2 fixed in photosynthesis that means food substances like carbohydrates, no net gaseous exchange takes place, it proteins and fats take place and as a is called compensation point. At this result of this, energy is produced where moment, the amount of oxygen released O2 is taken in and CO2 is liberated. The from photosynthesis is equal to the

145 Rate of High energy bonds Photosynthesis NH2 Compensation N O O O Point N O P O P O P OH N N O OH OH OH Adenine Phosphate groups

Rate of OH OH Respiration Ribose Adenosine Adenosine

Carbohydratre balance Monophosphate (AMP) Adenosine Time in a day (hours) Diphosphate (ADP) Adenosine Figure 14.2: Compensation point Triphosphate (ATP) amount of oxygen utilized in respiration. Figure 14.3: Molecular structure of ATP The two common factors associated with compensation point are CO2 and ATP is not only higher light (Figure 14.2). Based on this there energy compound are two types of compensation point. present in a cell. There They are CO2 compensation point and are other higher energy light compensation point. C3 plants have compounds also present. Example compensation points ranging from 40-60 GTP (Guanosine Tri Phosphate) and ppm (parts per million) CO2 while those UTP (Uridine Tri Phosphate). of C4 plants ranges from 1-5 ppm CO2.

14.3 Redox Reactions 14.2 Structure of ATP Respiration is responsible for generation NAD1 1 2e - 1 2H1 NADH 1 H1 - 1 of ATP. The discovery of ATP was made by FAD 1 2e 1 2H FADH 2 Karl Lohman (1929). ATP is a nucleotide When NAD1 (Nicotinamide Adenine consisting of a base-adenine, a pentose Dinucleotide-oxidised form) and FAD sugar-ribose and three phosphate groups. (Flavin Adenine Dinucleotide) pick up Out of three phosphate groups the last two electrons and one or two hydrogen ions are attached by high energy rich bonds (protons), they get reduced to NADH 1 H 1 (Figure 14.3). On hydrolysis, it releases and FADH2 respectively. When they drop energy (7.3 K cal or 30.6 KJ/ATP) and it is electrons and hydrogen off they go back found in all living cells and hence it is called to their original form. The reaction in universal energy currency of the cell. ATP which NAD1 and FAD gain (reduction) or is an instant source of energy within the lose (oxidation) electrons are called redox cell. The energy contained in ATP is used reaction (Oxidation reduction reaction). in synthesis carbohydrates, proteins and These reactions are important in cellular lipids. The energy transformation concept respiration. was established by Lipman (1941).

146 energy is released. Aerobic respiration is a Handy mnemonic very complex process and is completed in four major steps: 1. Glycolysis 2. Pyruvate oxidation (Link reaction) 3. Krebs cycle (TCA cycle) 4. Electron Transport Chain (Terminal oxidation).

14.4.2 Anaerobic respiration LEO the lion says GER In the absence of molecular oxygen glucose is incompletely degraded into either ethyl LEO - Loss of Electrons is Oxidation alcohol or lactic acid (Table 14.1). It GER - Gain of Electrons is Reduction includes two steps: 1. Glycolysis 14.4 Types of Respiration 2. Fermentation Respiration is classified into two types 14.5 Stages of Respiration as aerobic and anaerobic respiration (Figure 14.4) 1. Glycolysis-conversion of glucose into pyruvic acid in cytoplasm of cell.

14.4.1 Aerobic respiration 2. Link reaction-conversion of pyruvic acid into acetyl coenzyme-A in Respiration occurring in the presence mitochondrial matrix. of oxygen is called aerobic respiration. During aerobic respiration, food materials 3. Krebs cycle-conversion of acetyl like carbohydrates, fats and proteins are coenzyme A into carbon dioxide and water in the mitochondrial matrix. completely oxidised into CO2, H2O and

Respiration

Aerobic Respiration Anaerobic Respiration

Alcoholic Lactic acid Mixed acid fermentation fermentation fermentation

Figure 14.4: Types of Respiration

147 Table 14.1: Differences between aerobic and anaerobic respiration Aerobic respiration Anaerobic Respiration 1. It occurs in all living cells of higher It occurs yeast and some bacteria. organisms. 2. It requires oxygen for breaking the Oxygen is not required for breaking the respiratory substrate. respiratory substrate. The end products are alcohol, and CO 3. The end products are CO and H O. 2 2 2 (or) lactic acid. . 4. Oxidation of one molecule of glucose Only 2 ATP molecules are produced. produces 36 ATP molecules. 5. It consists of four stages-glycolysis, It consists of two stages-glycolysis and link reaction, TCA cycle and electron fermentation. transport chain. 6. It occurs in cytoplasm and mitochondria. It occurs only in cytoplasm.

4. Electron transport chain and oxidative molecule with energy in the form of phosphorylation remove hydrogen atoms ATP in mitochondrial inner membrane from the products of glycolysis, link (Figure 14.5). reaction and Krebs cycle release water

Glucose ADP+Pi

Ethyl alcohol + CO2 ATP Anaerobic 2 molecules of Pyruvic acid

Lactic acid Glycolysis Aerobic

k rea Lin ct io n 2NADH+H 2NADH+H +

+ 6NADH+H ATP

+

2 2 x Acetyl Co-A 2FADH2 ADP+Pi 2CO Krebs ETC Cycle 2 ADP+2 Pi 2 ATP O 2 HO2 4CO2

Figure 14.5: Overall stages of Respiration

148 E

Glucose c c c c c c S

1. Phosphorylaon 1 ATP A

Hexokinase H ADP P P Glucose-6-Phosphate c c c c c c Y

2. Isomerisaon 2 Phosphohexose isomerase R ++ O Mg P T

Fructose-6-Phosphate c c c c c c A ATP Phosphofructo kinase R

3. Phosphorylaon A 3 ++ ADP Mg P P P

Fructose-1,6-Bisphosphate c c c c c c E

4. Spling into R 4 Aldolase two molecules P P P c c c c c c Triose phosphate Glyceraldehyde- isomerase Dihydroxy Acetone 5.Isomerisaon 3-Phosphate 5 Phosphate

+ 2Pi 2NAD Glyceraldehyde-3-Phosphate

6.Oxidaon and + dehydrogenase Phosphorylaon 2NADH+H 6 P P 2x 1,3 Bisphospho Glycerate c c c

2ADP Phosphoglycerate kinase 7. Dephosphorylaon 2ATP 7 Mg++ P E 2x 3-Phospho Glycerate c c c S A

8. Shiing P from 8 Phosphoglyceromutase H ++

rd nd P 3 C to 2 C Mg P F 2x 2-Phospho Glycerate c c c F O 9 Enolase

2H2 O Y 9. Dehydraon ++ Mg A

P P 2x Phospho Enol Pyruvate c c c 2ADP Pyruvate kinase 10 ++ 2ATP Mg 10. Dephosphorylaon K++ 2x Pyruvate c c c

Figure 14.6: Glycolysis or EMP pathway

149 14.5.1 Glycolysis Check your grasp! (Gr: Glykos 5 Glucose, Lysis 5 Splitting) Glycolysis is a linear series of reactions in How many ATP molecules are which 6-carbon glucose is split into two produced from one sucrose molecule? molecules of 3-carbon pyruvic acid. The enzymes which are required for glycolysis 2. Pay off phase are present in the cytoplasm (Figure 14.6). Two molecules of glyceraldehyde-3- The reactions of glycolysis were worked phosphate oxidatively phosphorylated into out in yeast cells by three scientists Gustav two molecules of 1,3 - bisphospho glycerate. Embden (German), Otto Meyerhoff During this reaction 2NAD1 is reduced (German) and J Parnas (Polish) and so to 2NADH 1 H1 by glyceraldehyde- it is also called as . It is the EMP pathway 3- phosphate dehydrogenase at step 6. first and common stage for both aerobic Further reactions are carried out by and anaerobic respiration. It is divided different enzymes and at the end two into two phases. molecules of pyruvate are produced. In 1. Preparatory phase or endergonic this phase, 2ATPs are produced at step 7 phase or hexose phase (steps 1-5). and 2 ATPs at step10 (Figure 14.6). Direct 2. Pay off phase or oxidative phase or transfer of phosphate moiety from substrate exergonic phase or triose phase (steps molecule to ADP and is converted into 6-10). ATP is called substrate phosphorylation or direct phosphorylation or trans 1. Preparatory phase phosphorylation. During the reaction at Glucose enters the glycolysis from sucrose step 9, 2phospho glycerate dehydrated into which is the end product of photosynthesis. Phospho enol pyruvate a water molecule is Glucose is phosphorylated into glucose-6- removed by the enzyme enolase. As a result, phosphate by the enzyme hexokinase, and enol group is formed within the molecule. subsequent reactions are carried out by This process is called Enolation. different enzymes (Figure 14.6). At the end of this phase fructose-1, 6 - bisphosphate is 3. cleaved into glyceraldehyde-3- phosphate In the pay off phase totally 4ATP and and dihydroxy acetone phosphate by the 2NADH 1 H1 molecules are produced. enzyme aldolase. These two are isomers. Since 2ATP molecules are already Dihydroxy acetone phosphate is isomerised consumed in the preparatory phase, the into glyceraldehyde-3- phosphate by the net products in glycolysis are 2ATPs and enzyme triose phosphate isomerase, now 2NADH 1 H1. two molecules of glyceraldehyde 3 phosphate The overall net reaction of glycolysis enter into pay off phase. During preparatory C H O 1 2ADP 1 2Pi 1 2NAD1 phase two ATP molecules are consumed in 6 12 6 step-1 and step-3 (Figure 14.6). 1 2x CH3COCOOH 1 2ATP 12NADH12H

150 14.5.2 Pyruvate Oxidation (Link reaction) Sir Hans Adolf Two molecules of pyruvate formed by Krebs was born in glycolysis in the cytosol enters into Germany on 25th August 1900. He was the mitochondrial matrix. In aerobic awarded Nobel Prize respiration this pyruvate with coenzyme for his discovery of A is oxidatively decarboxylated into acetyl in CoA by pyruvate dehydrogenase complex. Physiology in 1953. This reaction is irreversible and produces

1 two molecules of NADH 1 H and 2CO2. It is also called transition reaction or Link reaction. The reaction of pyruvate oxidation is

1 2x CH3COCOOH 1 2NAD 1 2CoA Pyruvate dehydrogenase complex/ Mg11

1 2xCH3CO.CoA1 2NADH12H 1 F1 2CO2↑ Stalk

F Pyruvate dehydrogenase complex 0 consist of three distinct enzymes, Figure 14.7: Structure of such as 1. Pyruvate dehydrogenase TCA cycle starts with condensation 2. Dihydrolipoyil transacetylase of acetyl CoA with oxaloacetate in the 3. Dihydrolipoyil dehydrogenase presence of water to yield citrate or citric and five different coenzymes, TPP acid. Therefore, it is also known as Citric (Thymine Pyro Phosphate), NAD1, Acid Cycle (CAC) or Tri Carboxylic Acid FAD, CoA and lipoate. (TCA) cycle. It is followed by the action of different enzymes in cyclic manner. During the conversion of succinyl CoA to succinate 14.5.3 Krebs cycle or Citric acid cycle or by the enzyme succinyl CoA synthetase TCA cycle: or succinate thiokinase, a molecule of Two molecules of acetyl CoA formed from ATP synthesis from substrate without link reaction now enter into Krebs cycle. entering the electron transport chain is It is named after its discoverer, German called substrate level phosphorylation. In (1937). The Sir Hans Adolf Krebs animals a molecule of GTP is synthesized enzymes necessary for TCA cycle are found from GDP1Pi. In a coupled reaction GTP in mitochondrial matrix except succinate is converted to GDP with simultaneous dehydrogenase enzyme which is found in synthesis of ATP from ADP1Pi. In three mitochondrial inner membrane (Figure 14.7).

151 4. Oxidation 2. Dehydration 3. Rehydration Oxidation and 1. Condensation 6. Oxidation and decarboxylation decarboxylation c c c + 5. Decarboxylation c c c c c c c c c c c c c c c c c c c c + 2 HO 2 e NADH+H 2 t HO e e t a NAD t r c c CO c a + 2 a 4 t 3 a Co A r 5 i c c c t t ++ i n CO u l c ++ o 2 e g o Mn c t Fe + s o a I t a r t s e Co A C i i NADH+H k 6 2 - C C Oxalosuccinate NAD HO α c c CoA c Pyruvate dehydrogenase Aconitase c 1 c Aconitase 2 A o Oxalosuccinate decarboxylase Isocitrate dehydrogenase c CO ketoglutarate Co A C − l c dehydrogenase α y c n c i c c + CoA c Citrate synthase u + Pyruvate Acetyl CoA S e H t NAD + a Krebs cycle or Citric acid cycle Citric cycle or Krebs 2 t H 7 HO e D Succinyl synthetase Co-A e c A t a Malate dehydrogenase a N c c o l n Co A e i e c c a t t Succinate dehydrogenase c x Fumarase a a c r l Figure 14.8: Figure O u a a P 10 ADP+Pi S 9 T c A M m + 8 c u + F c 2 D HO A c c c N c c NADH+H c c FAD c c 2 e l c FADH y c s b e r Link Reaction 7. Hydration and Phosphorylation 8.Oxidation 9. Hydration 10. Oxidation K

152 steps (4, 5, 9) in this cycle NAD1 is reduced Two molecules of pyruvic acid formed to NADH1 H1 and at step 7 (Figure14.8) at the end of glycolysis enter into the where FAD is reduced to FADH2. mitochondrial matrix. Therefore, Krebs The summary of link reaction and cycle is repeated twice for every glucose Krebs cycle in Mitochondria is molecule where two molecules of pyruvic acid produces six molecules of CO eight 1 2, Pyruvic acid 1 4NAD 1 FAD 1 4H2O 1 ADP1Pi molecules of NADH 1 H1, two molecules Mitochondrial matrix. of FADH2 and two molecules of ATP. 1 3CO21 4NADH14H 1FADH 2 1H2O1ATP.

Fats Carbohydrates Proteins Proteases

Fatty acids Glycerol Glucose Amino acids

o

Fructose-1,6-Bisphosphate i

t

a

n

i

m

a

DHAP Glyceraldehyde e -3-Phospate Dn

Pyruvic acid

CO2 Acetyl CoA

Krebs NH2 cycle

HO2 CO2

Figure 14.9: Alternative substrates for respiration

153 1. Significance of Krebs cycle: through pyruvic acid or acetyl CoA and it 1. TCA cycle is to provide energy in the depends upon the structure. So respiratory form of ATP for metabolism in plants. intermediates form the link between 2. It provides carbon skeleton or raw synthesis as well as breakdown. The citric material for various anabolic processes. acid cycle is the final common pathway for oxidation of fuel molecules like amino 3. Many intermediates of TCA cycle are acids, fatty acids and carbohydrates. further metabolised to produce amino Therefore, respiratory pathway is an acids, proteins and nucleic acids. amphibolic pathway (Figure 14.9). 4. Succinyl CoA is raw material for formation of chlorophylls, cytochrome, 14.5.4 Electron Transport Chain (ETC) phytochrome and other pyrrole (Terminal oxidation) substances. During glycolysis, link 5. α-ketoglutarate and oxaloacetate reaction and Krebs undergo reductive amination and cycle the respiratory produce amino acids. substrates are oxidised 6. It acts as metabolic sink which plays a at several steps and as a central role in intermediary metabolism. result many reduced coenzymes NADH 1 H1 and FADH are produced. These 2. Amphibolic nature 2 reduced coenzymes are transported to Krebs cycle is primarily a catabolic inner membrane of mitochondria and pathway, but it provides precursors for are converted back to their oxidised various biosynthetic pathways there by forms produce electrons and protons. In an anabolic pathway too. Hence, it is mitochondria, the inner membrane is called . It serves as amphibolic pathway folded in the form of finger projections a pathway for oxidation of carbohydrates, towards the matrix called cristae. In cristae fats and proteins. When fats are respiratory many oxysomes (F particles) are present substrate they are first broken down 1 which have electron transport carriers are into glycerol and fatty acid. Glycerol is present. According to converted into DHAP and acetyl CoA. Peter Mitchell’s this electron This acetyl CoA enter into the Krebs Chemiosmotic theory transport is coupled to ATP synthesis. cycle. When proteins are the respiratory Electron and hydrogen(proton) transport substrate they are degraded into amino takes place across four multiprotein acids by proteases. The amino acids after complexes(I-IV). They are deamination enter into the Krebs cycle 1. Complex-I (NADH dehydrogenase). The synthesis of It contains a flavoprotein(FMN) and glucose from certain associated with non- iron Sulphur non-carbohydrate protein (Fe-S). This complex is responsible carbon substrates for passing electrons and protons from such as proteins and lipids are called mitochondrial NADH (Internal) to gluconeogenesis. Ubiquinone(UQ).

154 1 1 (A and B) and cytochromes a and a NADH 1 H 1 UQ NAD 1 UQH2 3. Complex IV is the terminal oxidase and In plants, an additional NADH brings about the reduction of 1/2 O to dehydrogenase (External) complex is 2 present on the outer surface of inner H2O.Two protons are needed to form a membrane of mitochondria which can molecule of H2O (terminal oxidation).

1 oxidise cytosolic NADH 1 H . 1 2Cyt coxidised 1 2H 1 1/2 O2 2Cyt creduced 1H2O Ubiquinone (UQ) or Coenzyme Quinone(Co Q) is a small, lipid soluble The transfer of electrons from electron, proton carrier located within the reduced coenzyme NADH to oxygen inner membrane of mitochondria. via complexes I to IV is coupled to the synthesis of ATP from ADP and inorganic

2. Complex-II (Succinic dehydrogenase) phosphate (Pi) which is called It contains FAD flavoprotein is associated Oxidative . The F F -ATP synthase with non-heme iron Sulphur (Fe-S) phosphorylation 0 1 (also called complex V) consists of F protein. This complex receives electrons 0 and F . F converts ADP and Pi to ATP and protons from succinate in Krebs cycle 1 1 and is attached to the matrix side of the and is converted into fumarate and passes inner membrane. F is present in inner to ubiquinone. 0 membrane and acts as a channel through Succinate 1 UQ → Fumarate 1 UQH 2 which protons come into matrix.

3. Complex-III (Cytochrome bc1 com- Oxidation of one molecule of plex) This complex oxidises reduced ubi- NADH 1 H1 gives rise to 3 molecules quinone (ubiquinol) and transfers the elec- of ATP and oxidation of one molecule trons through Cytochrome bc Complex 1 FADH 2 produces 2 molecules of ATP (Iron Sulphur center bc1 complex) to cy- within a mitochondrion. But cytoplasmic tochrome c. Cytochrome c is a small pro- NADH 1 H1 yields only two ATPs tein attached to the outer surface of inner through external NADH dehydrogenase. membrane and act as a mobile carrier to Therefore, two reduced coenzyme transfer electrons between complex III to (NADH 1 H1) molecules from glycolysis complex IV. being extra mitochondrial will yield

1 2 3 2 5 4 ATP molecules instead of UQH2 12Cyt coxidised UQ12Cyt creduced 12H 6 ATPs (Figure 14.10). The Mechanism of mitochondrial ATP synthesis is based Ubiquinone and on Chemiosmotic hypothesis. According cytochrome bc complex 1 to this theory electron carriers present are structurally and in the inner mitochondrial membrane functionally similar allow for the transfer of protons (H1). to plastoquinone and cytochrome b f 6, For the production of single ATP, complex respectively in the photosynthetic 3 protons (H1) are needed. The terminal electron transport chain. oxidation of external NADH bypasses the first phosphorylation site and hence 4. Complex IV (Cytochome c oxidase) only two ATP molecules are produced This complex contains two copper centers per external NADH oxidised through

155 288.247 pt

Figure 14.10: Electron Transport Chain and Terminal Oxidation mitochondrial electron transport chain. Recent view However, in those animal tissues in which When the cost of transport of ATPs from malate shuttle mechanism is present, the matrix into the cytosol is considered, oxidation of external NADH will yield the number will be 2.5 ATPs for each almost 3 ATP molecules. 1 1 NADH H and 1.5 ATPs for each FADH2 oxidised during electron transport system. Abnormal rise in Therefore, in plant cells net yield of 30 ATP respiratory rate of molecules for complete aerobic oxidation of ripening in fruits is one molecule of glucose. But in those animal called Climacteric. cells (showing malate shuttle mechanism) Examples are apple, banana, mango, net yield will be 32 ATP molecules. papaya, pear. Electron transport chain inhibitors 1. 2,4 DNP (Dinitrophenol) - It prevents Complete oxidation of a glucose synthesis of ATP from ADP, as it directs molecule in aerobic respiration results in electrons from Co Q to O the net gain of 2 36 ATP molecules in plants 2. - It prevents flow of electrons as shown in table 14.2. Since huge amount Cyanide from Cytochrome a to O of energy is generated in mitochondria 3 2 in the form of ATP molecules they are 3. Rotenone - It prevents flow of electrons from NADH 1 H1/FADH to Co Q called ‘power house of the cell’. In the 2 case of aerobic prokaryotes due to lack of 4. Oligomycin – It inhibits oxidative mitochondria each molecule of glucose phosphorylation produces 38 ATP molecules.

156 Volume of CO liberated RQ 5 2 Peter Mitchel, a British Volume of O2 consumed Biochemist received Nobel 1. The respiratory substrate is a prize for Chemistry in 1978 carbohydrate, it will be completely for his work on the coupling oxidised in aerobic respiration and the of oxidation and value of the RQ will be equal to unity. phosphorylation in mitochondria.

C6H12O6 1 6O2 6CO2 ↑ 1 6H2O 1 Energy Glucose 6 molecules of CO Cyanide resistant RQ of glucose 5 2 6 molecules of O respiration is believed 2 to be responsible for 5 1 (unity) the climacteric in fruits 2. If the respiratory substrate is a Cyanide resistant respiration is carbohydrate it will be incompletely known to generate heat in thermogenic oxidised when it goes through anaerobic tissues. respiration and the RQ value will be The amount of heat produced in infinity. thermogenic tissues may be as high as C6H12O6 2CO2↑1 2C2H5OH 1 Energy 51°C. Glucose Ethyl alcohol RQ of glucose 2 molecules of CO 5 2 Anaerobically } zero molecule of O 14.6 Respiratory Quotient (RQ) 2 5 ∞ (infinity) The ratio of volume of carbon dioxide 3. In some succulent plants like O given out and volume of oxygen taken in puntia, carbohydrates are partially during respiration is called Bryophyllum Respiratory oxidised to organic acid, particularly . RQ value Quotient or Respiratory ratio malic acid without corresponding release depends upon respiratory substrates and of CO but O is consumed hence the RQ their oxidation. 2 2 value will be zero.

Table 14.2: Net Products gained during aerobic respiration per glucose molecule.

1 Reduced Total ATP Stages CO2 ATP Reduced NAD FAD Production 2 Glycolysis 0 2 06 (2 3 2 5 4) 2 Link reaction 2 0 06 (2 3 3 5 6) 6 2 Krebs cycle 4 2 24 (6 3 3 5 18) (2 3 2 5 4)

Total 6 4 ATPs 28 ATPs 4 ATPs 36 ATPs

157 2C6H12O6 1 3O2 3C4H6O5 1 3H2O 1 Energy Glucose Malic acid

RQ of glucose zero molecule of CO 5 2 in succulents 3 molecules of O2 5 0 (zero) 4. When respiratory substrate is protein or fat, then RQ will be less than unity.

2(C51H98O6) 1 145O2 102CO2↑1 98H2O 1 Energy Tripalmitin(Fat) RQ of 102 molecules of CO 5 2 Tripalmitin 145 molecules of O2 5 0.7 (less than unity)

5. When respiratory substrate is an organic acid the value of RQ will be more than unity.

C4H6O5 1 3O2 4CO2 ↑1 3H2O 1 Energy Malic acid The apparatus used for determining RQ of 4 molecules of CO respiration and RQ is called Ganong’s 5 2 malic acid Respirometer. 3 molecules of O2 5 1.33 (more than unity) Respiratory quotients of some other Significance of RQ substances 1. RQ value indicates which type of Proteins : 0.8–0.9 respiration occurs in living cells, either Oleic acid (Fat) : 0.71 aerobic or anaerobic. Palmitic acid (Fat) : 0.36 2. It also helps to know which type of Tartaric acid : 1.6 respiratory substrate is involved. Oxalic acid : 4.0

Red colour in various parts of plants is Experiment to demonstrate the due to the presence production of CO2 in aerobic of anthocyanin, respiration Take small quantity of any seed synthesis of which require more O2 (groundnut or bean seeds) and allow than CO2 evolved. RQ will be less than one. them to germinate by imbibing them. While they are germinating place them in a conical flask. A small glass tube containing 4 ml of freshly prepared

158 Potassium hydroxide (KOH) solution Activity is hung into the conical flask with the help of a thread and tightly close the Take a test tube with some germinated one holed cork (Figure 14.11). Take seeds and fill with water. Keep this test a bent glass tube, the shorter end of tube after some time until liberation of which is inserted into the conical CO When the carbon dioxide from 2. flask through the hole in the cork, respiration is mixed to water, carbonic while the longer end is dipped in a acid (H2CO3) is produced. Therefore, beaker containing water. Observe the as more carbon dioxide is released, position of initial water level in bent the solution becomes more acidic. You glass tube. This experimental setup will see changes in pH as an indicator is kept for two hours and the seeds using blue litmus paper changed into were allowed to germinate. After red that respiration has occurred two hours, the level of water rises in CO21H2O H2CO3 the glass tube. It is because, the CO2 evolved during aerobic respiration by 14.7 Anaerobic Respiration germinating seeds will be absorbed by KOH solution and the level of water 14.7.1 Fermentation will rise in the glass tube. Some organisms can respire in the absence of CO2 1 2KOH —> K2CO3 1H2O oxygen. This process is called fermentation or anaerobic respiration (Figure 14.12). There are three types of fermentation: 1. Alcoholic fermentation 2. Lactic acid fermentation Figure 14.11: Demonstration of 3. Mixed acid fermentation production of CO2 during respiration In the case of groundnut or bean 1. Alcoholic fermentation seeds, the rise of water is relatively The cells of roots in water logged soil respire lesser because these seeds use fat and by alcoholic fermentation because of lack proteins as respiratory substrate and of oxygen by converting pyruvic acid into ethyl alcohol and CO . Many species of yeast release a very small amount of CO2. 2 But in the case of wheat grains, the (Saccharomyces) also respire anaerobically. rise in water level is greater because This process takes place in two steps: Pyruvate they use carbohydrate as respiratory decarboxylase (i) 2CH3COCOOH 2CH3CHO 12CO2↑ TPP substrate. When carbohydrates are Pyruvic acid Alcohol Acetaldehyde dehydrogenase 1 1 used as substrate, equal amounts of (ii) 2CH3CHO 1 2NADH12H 2CH3CH2OH 1 2NAD

Acetaldehyde Ethyl alcohol CO2 and O2 are evolved and consumed.

159 Table 14.3: Comparison of alcoholic fermentation and lactic acid fermentation Alcoholic fermentation Lactic acid fermentation

1. It produces alcohol and releases CO2 It produces lactic acid and does not release

from pyruvic acid. CO2 from pyruvic acid. 2. It takes place in two steps. It takes place in single step. 3. It involves two enzymes, pyruvate It uses one enzyme, lactate dehydrogenase decarboxylase with Mg11 and alcohol with Zn11. dehydrogenase. 4. It forms acetaldehyde as intermediate Does not form any intermediate compound. compound.

Occurs in bacteria, some fungi and 5. It commonly occurs in yeast. vertebrate muscles.

Industrial uses of alcoholic 3. In producing vinegar and in tanning, fermentation: curing of leather. 1. In bakeries, it is used for preparing 4. Ethanol is used to make gasohol (a fuel bread, cakes, biscuits. that is used for cars in Brazil). 2. In beverage industries for preparing wine and alcoholic drinks.

Glucose

Net gain of 2 ATP

+ 2NAD

+ 2NADH+H

2 x Pyruvic Acid

+ + 2 x NADH+H 2 x NADH+H

+ + 2 x NAD 2 x NAD Alcohol dehydrogenase Lactate dehydrogenase

2 x Ethyl alcohol + CO2 2 x Lactic Acid Alcoholic fermentation Lactic acid fermentation

Figure 14.12: Anaerobic Respiration

160 2. Lactic acid fermentation Table 14.5: Net products from one Some bacteria (Bacillus), fungi and molecule of Glucose under Glycolysis and muscles of vertebrates produce lactic acid Anaerobic respiration. from pyruvic acid (Table 14.3). Substrate Reduced Total 2CH COCOOH 1 2NADH12H1 Stage level ATP 1 3 NAD ATP Pyruvic acid Lactate dehydrogenase production

1 Glycolysis 2 2* 8 2CH3CHOHCOOH 1 2NAD Lactic acid 2 reduced Anaerobic 2 NAD1 r e - 2 3. Mixed acid fermentation respiration oxidised This type of fermentation is a characteristic feature of Enterobacteriaceae and results *One reduced NAD1 equivalent to 3 ATPs in the formation of lactic acid, ethanol, formic acid and gases like CO and H 2 2. Check your grasp! Characteristics of Anaerobic Respiration • Why respire 1. Anaerobic respiration is less efficient anaerobically? than the aerobic respiration (Figure 14. 12) • Does anaerobic respiration take (Table 14.4). place in higher plants? 2. Limited number of ATP molecules is generated per glucose molecule (Table 14.5). Demonstration of alcoholic 3. It is characterized by the production of fermentation Take a Kuhne’s fermentation tube CO2 and it is used for Carbon fixation in photosynthesis. which consists of an upright glass tube with side . Pour 10% sugar Table 14.4: Comparison between glycolysis solution mixed with baker’s yeast and fermentation into the fermentation tube the side Glycolysis Fermentation tube is filled plug the mouth with lid. After some time, the glucose solution 1. Glucose is Starts from pyruvic will be fermented. The solution will converted into acid and is converted give out an alcoholic smell and level pyruvic acid. into alcohol or lactic acid. of solution in glass column will fall

2. It takes place in It takes place in the due to the accumulation of CO2 gas. the presence or absence of oxygen. It is due to the presence of zymase absence of oxygen. enzyme in yeast which converts the 3. Net gain is 2ATP. No net gain of ATP glucose solution into alcohol and molecules. CO2. Now introduce a pellet of KOH 4. 2NADH 1 H1 2NADH 1 H1 into the tube, the KOH will absorb molecules are molecules are CO2 and the level of solution will produced. utilised. rise in upright tube (Figure 14.13).

161 Activity Take a bottle filled with warm water CO 2 mixed with baker’s yeast and sugar. After some time, you will notice water bubbling as yeast produces carbon dioxide. Attach a balloon to the mouth of the bottle. Sugar solution and Yeast After 30 minutes you’ll notice balloon standing upright (Figure 14.14).

Why the balloon has inflated?

Yeast & sugar in warm water were poured into a bottle After 15 minutes. After 30 minutes.

Sugar Sugar Sugar

Figure 14.13: Kuhne’s Figure: 14.14: Air balloon activity fermentation experiment

14.8 Factors Affecting Respiration Factors affecting Respiration The amount of protoplasm and its state of activity Optimum temperature for External influence the rate of Internal respiration is 30ºC. At low respiration Factors Factors temperatures and very high temperatures rate of respiration Concentration of respiratory decreases substrate is proportional to the rate of respiration When sufficient amount of O is available the rate of Wounding of plant 2 aerobic respiration will be organs stimulates optimum and anaerobic the rate of respiration respiration is completely stopped. in that region. This is called Extinction point. Rate of respiration decreases with decreasing amount of water. Proper hydration High concentration of CO2 is essential for respiration reduces the rate of respiration Some chemical substance A plant or tissue transferred acts as inhibitors. from water to salt solution Example: Cyanides will increase the rate of Light is an indirect factor respiration. It is called affecting the rate of respiration salt respiration

162 or Direct Oxidative Pathway. It consists How alcoholic beverages of two phases, oxidative phase and non- like beer and wine is oxidative phase. The oxidative events made? convert six molecules of six carbon The conversion of Glucose-6-phosphate to 6 molecules pyruvate to ethanol takes place in malted of five carbon sugar Ribulose-5 barley and grapes through fermentation. phosphate with loss of 6CO2 molecules Yeasts carryout this process under and generation of 12 NADPH 1 H1 anaerobic conditions and this conversion (not NADH). The remaining reactions increases ethanol concentration. If the known as non-oxidative pathway, convert concentration increases, it’s toxic effect Ribulose-5-phosphate molecules to kills yeast cells and the left out is called various intermediates such as Ribose-5- beer and wine respectively. phosphate(5C), Xylulose-5-phosphate(5C), Glyceraldehyde-3-phosphate(3C), 14.9 Pentose Phosphate Pathway Sedoheptulose-7-Phosphate(7C), and Erythrose-4-phosphate(4C). Finally, five (Phospho Gluconate Pathway) molecules of glucose-6-phosphate is During respiration breakdown of glucose regenerated (Figure 14.16). The overall in cytosol occurs both by glycolysis reaction is: (about 2/3) as well as by oxidative pentose 1 1 1 phosphate pathway (about 1/3). Pentose 6 x Glucose-6-Phosphate 12NADP 6H2O phosphate pathway was described by 1 1 1 Warburg, Dickens and Lipmann (1938). 5 x Glucose-6-Phosphate 6CO2 Pi 1 1 Hence, it is also called Warburg-Dickens- 12NADPH 12H Lipmann pathway. It takes place in The net result of complete oxidation cytoplasm of mature plant cells. It is an of one glucose-6-phosphate yield 6CO2 alternate way for breakdown of glucose and 12NADPH 1 H1. The oxidative (Figure 14.15). pentose phosphate pathway is controlled It is also known as Hexose by glucose-6-phosphate dehydrogenase monophosphate shunt (HMP Shunt) enzyme which is inhibited by high ratio of NADPH to NADP1.

Starch

Oxidation Pentose via Glucose phosphate Pathway Oxidation via glycolysis

Ribulose- 5-phosphate Pyruvic acid

Figure 14.15: Fate of Glucose in HMP shunt and Glycolysis

163 + 2. Hydration 1. Oxidation + Decarboxylation + 3. Oxidation and 2 2 6H O 6CO 6 x NADPH+H + 6 x NADP 3 2 Lactonase 6 x NADPH+H 6 x NADP 1 36 C 30 C 30 C 36 C 6-Phospho Gluconate Ribulose-5-Phosphate 6-Phospho gluconate dehydrogenase 6-Phospho Gluconolactone 6 X 6 X

OXIDATIVE PHASE 6 X 36 C Glucose-6-Phosphate dehydrogenase 4 Glucose-6-Phosphate 6 6 X Pentose phosphate pathway or HMP shunt or pathway phosphate Pentose 5 NON OXIDATIVE PHASE Hexokinase Figure 14.16: Figure phosphorylated compounds phosphorylated sugars 30 C 6C 30 C such as 3C,such 4C, 5C and 7C P ADP 4. Formation of T A Various intermediate compounds Various Fructose-6-Phosphate 6C Phospho hexose isomerase Phospho hexose 5 X Glucose-6-Phosphate Glucose Phosphorylation 5. Conversion 6. Isomerisation

164 Significance of pentose phosphate pathway Summary 1 HMP shunt is associated with the Respiration is a biological process in which generation of two important products, energy is released by breaking down of NADPH and pentose sugars, which play a vital complex organic substances into simple role in anabolic reactions. compounds. The respiratory substrates may 2 Coenzyme NADPH generated is used for be carbohydrate, protein or fats. Respiration is reductive biosynthesis and counter damaging of two types, aerobic (with O2) and anaerobic the effects of oxygen free radicals (without O2). All plants, animals and most 3 Ribose-5-phosphate and its derivatives of the microbes derive energy from aerobic are used in the synthesis of DNA, RNA, ATP, respiration. Some bacteria and fungi like yeast NAD1, FAD and Coenzyme A. show anaerobic respiration. Aerobic respiration 4 Erythrose is used for synthesis of consists of four stages and they are glycolysis, anthocyanin, lignin and other aromatic link reaction, TCA cycle and ETS. Glycolysis compounds. is the first stage which occurs in cytosol and common for both aerobic and anaerobic respiration and it involves breaking down of

165 glucose into two molecules of pyruvic acid. molecules produced in plants are Acetyl CoA formed from pyruvic acid, acts as a a. 3 b. 4 c. 6 d. 8 link between glycolysis and Krebs cycle. Krebs 3. The compound which links glycolysis and cycle takes place in matrix of mitochondria Krebs cycle is and also called as citric acid cycle in which CO 2 a. succinic acid b. pyruvic acid and H O were produced. Hydrogen removed 2 c. acetyl CoA d. citric acid from the substrates is received by coenzymes which get reduced. They are again oxidised by 4. Assertion (A): Oxidative phosphorylation removal of hydrogen. This hydrogen splits into takes place during the electron transport protons and electrons. The electrons transferred chain in mitochondria. through various electron transport carriers Reason (R): Succinyl CoA is present in inner membrane of mitochondria is phosphorylated into succinic acid by used for the synthesis of ATP with the help of substrate phosphorylation. ATP synthase. This process is called oxidative a. A and R is correct. R is correct phosphorylation. explanation of A Anaerobic respiration involves incomplete b. A and R is correct but R is not the breaking down of the substrate glucose correct explanation of A into ethyl alcohol or lactic acid. In aerobic c. A is correct but R is wrong respiration 36 ATP molecules are produced d. A and R is wrong. in plant mitochondria but in animals 38 ATP 5. Which of the following reaction is not molecules are produced per glucose molecule. involved in Krebs cycle. During anaerobic respiration only 2 ATP a. Shifting of phosphate from 3C to 2C molecules are produced, therefore anaerobic b. Splitting of Fructose 1,6 bisphosphate respiration is less efficient than aerobic of into two molecules 3C compounds. respiration. The respiratory quotient (RQ) c. Dephosphorylation from the is the ratio of carbon dioxide production to substrates oxygen consumption and reflects the relative d. All of these contributions of fat, carbohydrate, and protein to the oxidation. Pentose phosphate pathway is 6. What are enzymes involved in an alternative pathway to glycolysis and TCA phosphorylation and dephosphorylation cycle for oxidation of glucose. It occurs in reactions in EMP pathway? cytoplasm of both prokaryotes and . 7. Respiratory quotient is zero in succulent plants. Why? Evaluation 8. Explain the reactions taking place in 1. The number of ATP mitochondrial inner membrane. molecules formed by 9. What is the name of alternate way of complete oxidation of glucose breakdown? Explain the process one molecule of pyruvic involved in it? acid is 10. How will you calculate net products of a. 12 b. 13 c. 14 d. 15 one sucrose molecule upon complete 2. During oxidation of two molecules of oxidation during aerobic respiration as cytosolic NADH 1 H1, number of ATP per recent view?

166 t ICT Corner Rate of respiration

Let’s estimate rate of respiration

Steps • Scan the QR code or go to google play store • Type online labs and install it. • Select biology and select rate of respiration • Click theory to know the basic about respiration • Register yourself with mail-id and create password to access online lab simulations

Activity • Press simulation to do the rate of respiration. • Conclude your observations.

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167 Chapter 15 Plant Growth and Development

seedling? How does a new plant structure Learning Objectives arise from the pre-existing structure? Growth The learner will be able to, is defined as an irreversible permanent increase in size, shape, number,volume • Define growth. and dry weight. Plant growth occurs by cell • List out and differentiate the phases division, cell enlargement, differentiation of growth. and maturation. • Understand the ways of measuring Bamboos are evergreen growth. grasses and certain • Explain the structure, precursor, species of it can grow bioassay and physiological effects at the rate of growth 91 of plant growth regulators. cm per day. The Saguaro is a tree like cactus and is a slow Chapter Outline growing plant. The rate of growth is one inch in the first ten years and it does not 15.1 Characteristics of growth begin to until it is about 60 years 15.2 Plant growth regulators old. It’s lifespan exceeds 150 years and takes 75–100 years to grow a side arm. 15.3 Plant movements 15.4 Photoperiodism 15.5 Vernalization 15.6 Seed germination and dormancy 15.7 Senescence 15.8 Stress physiology

The Banyan tree continues to grow for 15.1 Characteristics of Growth thousands of years and some others • Growth increases in protoplasm at particularly annual plants cease growth cellular level. within a season or within a year. Can you • Stem and roots are indeterminate in understand the reasons? How does a zygote growth due to continuous cell division give rise to an embryo and an embryo to a and is called open form of growth.

168 15.1.2 Phases of growth Growth is measurable, it is There are three phases of growth, amazing to know that 1. Formative phase one single maize root 2. Elongation phase apical meristem can give rise to more 3. Maturation phase than 17,500 new cells per hour and 1. Formative phase: Growth in this phase cells in a watermelon may increase in occurs in meristematic cells of shoot and size upto 3,50,000 times. root tips. These cells are small in size, have dense protoplasm, large nucleus and • The primary growth of the plant is due small vacuoles. Cells divide continuously to the activity of apical meristem where, by mitotic cell division. Some cells retain new cells are added to root and shoot capability of cell division while other cells apex causing linear growth of plant body. enter the next phase of growth (Figure 15.1). • The secondary vascular cambium and 2. Elongation Phase: Newly formed cork cambium add new cells to cause daughter cells are pushed out of the increase in girth. meristematic zone and increases the volume. • Leaves, flowers and fruits are limited It requires auxin and food supply, deposition in growth or of determinate or closed of new cell wall materials (intussusception), form growth. addition of protoplasm and development of • Monocarpic annual plants produce central vacuole take place. flowers only once during lifetime and 3. Maturation Phase: During this dies. Example: Paddy and Bean stage cells attain mature form and size. • Monocarpic perennials produce Thickening and differentiation takes flowers only once during life time place. After differentiation, the cells do but the plants survive for many years. not grow further. Example: Bamboo. Activity • Polycarpic perennials produce flowers every year during life time. Example: Demonstration of phases of growth Coconut. To demonstrate and study the phases of growth, germinate a few seeds of 15.1.1 Indication of growth bean on a circular filter paper soaked Growth in plants can be measured in with water in a petridish. After two terms of, days of growth, select a few seedlings i. Increase in length or girth (roots and with straight radical of 2 to 3 cm stems) length. Dry the surface of radical with ii. Increase in fresh or dry weight a blotting paper and mark the radical iii. Increase in area or volume (fruits and from tip to base with at least 2 mm leaves) gap using water proof ink. Replace the seedlings in filter paper and observe iv. Increase in number of cells produced. further growth.

169 tip of the stem, root and branches. It is the initial stage of growth. In other words, growth starts from this period (Figure 15.2).

Maturation Phase ii. Log phase or exponential growth Here, the newly formed cell increases Elongation Phase in size rapidly by deposition of cell wall ? Formative Phase material. Growth rate is maximum and Figure 15.1: Phases of growth in root reaches top because of cell division and physiological processes are quite fast. 15.1.3 Kinetics of growth The volume of protoplasm also increases. It is an analysis of the of cells or It results in rapid growth and causes expansion. elongation of internode in the stem.

1. Stages in Growth rate iii. Decelerating phase or Decline phase The total period from initial to the final or slow growth phase stage of growth is called the grand period The rate of growth decreases and becomes of growth. The total growth is plotted limited owing to internal and external or against time and ‘S’ shaped sigmoid both the factors because the metabolic curve (Grand period curve) is obtained. process becomes slow. It consists of four phases (Figure 15.2). They are: iv. Steady state period or maturation i. Lag phase phase ii. Log phase In this phase cell wall thickening due iii. Decelerating phase to new particle deposition on the inner surface of the cell wall takes place. The iv. Maturation phase overall growth ceases and becomes i. Lag phase constant. The growth rate becomes zero. In this phase new cells are formed from pre-existing cells slowly. It is found in the 2. Types of growth rate The increased growth per unit time is termed as growth rate. An organism or Maturation Phase part of an organism can produce more cells Decelerating Phase through arithmetic growth or geometric growth or both.

i. Arithmetic Growth Rate

Log Phase If the length of a plant organ is plotted against time, it shows a linear curve and this growth is called . Size / Weight ofSize / Weight the organ Lag Phase arithmetic growth Time • The rate of growth is constant and it increases in an arithmetic manner. Figure 15.2: Stages in growth rate

170 • Only one cell is allowed to divide between the two-resulting progeny cell. • One continues to divide but the other t

undergoes cell cycle arrest and begins n a to develop, differentiate and mature. l p

e C h

• After each round of cell division, only t f

a single cell remains capable of division o t D h g

and one new body cell forms. i e

For example, starting with a single cell H after round 1 of cell division there is one dividing cell and one body cell. After round 2 there are two body cells, after round 3 Time there are three and so on (Figure 15.3). Figure 15.4: Constant Linear Growth

Dividing cell hair next to other epidermal cells. Hair may Body Cell contain 5 to 10 cells by the division of the basal cell. So, all its cells could be produced in just five to ten days. In the figure 15.4, on plotting the hight of the plant against time a linear curve is obtained. Mathematically it is expressed as:

Lt 5 Lo + rt 5 length at time ‘t’ Lt 5 length at time zero Lo r 5 growth rate of elongation per unit ii. Geometric growth rate: This growth occurs in many higher plants Arithmetic Growth Rate Figure 15.3: and plant organs and is measured in size The plants single dividing cell would or weight. In plant growth, geometric cell undergo one million rounds of nuclear and division results if all cells of an organism cellular division. If each round requires one or tissue are active mitotically. Example: day, this type of arithmetic increase would Round three in the given figure 15.5, require one million days or 2739.7 years. produces 8 cells as 23 5 8 and after round This arithmetic rate is capable of producing 20 there are 220 5 1,048,576 cells. small number of cells present in very small The large plant or animal parts are parts of plants. For example the hair on produced this way. In fact, it is common many leaves and stems consists of just a in animals but rare in plants except when single row of cells produced by the division they are young and small. Exponential of the basal cell, the cell at the bottom of the growth curve can be expressed as,

171 Mother cell

2 Progeny cells

4 Progeny cells

8 Progeny cells Figure 15.5: Geometric growth

5 rt W1 W0e 5 Final size (weight, height and W1 number) 5 Initial size at the beginning of the W0 period r 5 Growth rate t 5 Time of growth e 5 Base of the natural logarithms Figure 15.6: Arithmetic and geometric growth of embryo Here ‘r’ is the relative growth rate and also a measure of the ability of the plant to Quantitative comparisons between the produce new plant material, referred to as growth of living system can also be made efficiency index. Hence, the final size of in two ways and is explained in the table 1. depends on the initial size W1 W0. In figure 15.7, two leaves A and B are drawn at a particular time. Then A1and iii. Arithmetic and Geometric Growth B1 are drawn after a given time. A and of Embryo B 5 Area of leaves at a particular time. A1 Plants often grow by a combination and B1 5 Area of leaves after a given time. of arithmetic and geometric growth (A1-A) and (B1-B) represents an absolute patterns. A young embryonic plant grows increase in area in the given time. Leaf A geometrically and cell division becomes restricted to certain cells at the tips of roots Table 1: Comparison between absolute and and shoots. After this point, growth is of relative growth rates the slower arithmetic type, but some of the Absolute growth rate Relative growth rate Increase in total The growth of the new cells that are produced can develop into growth of two organs given system per unit their mature condition and begin carrying measured and time expressed per out specialized types of metabolism compared per unit unit initial parameter (Figure 15. 6). Plants are thus a mixture of time is called absolute is called relative older, mature cells and young, dividing cells. growth rate. growth rate.

172 increases from 5 cm2 to 10 cm2; 5 cm2 in a in carbon-di-oxide and hydrogen in water given time. Leaf B increases from 50 cm2 are assimilated in photosynthesis. to 55 cm2 ; 5 cm2 in a given time. Hence, c. Temperature both leaves A and B increase their area Temperature plays a significant role in by 5 cm2 in a given time. This is absolute the growth of the plant. Proper growth growth. Relative growth is faster in leaf A of a plant occurs at a about 28o C to 30o C because of initial small size. It decreases temperature and above 45o C will damage with time (Figure 15.7). the protoplasm and hinders the growth. d. Oxygen Oxygen has a vital role in the growth of the plant. It helps in releasing metabolic energy essential for growth activities. It is necessary for respiration. e. Light Light has its own contribution in the growth of the plant. Light is important for growth and photosynthesis. Light stimulates healthy growth. Absence of Figure 15.7: Diagrammatic comparision of light may lead to yellowish in colour. This absolute and relative growth rates is called etiolation. II. Internal Factors 3.Conditions of growth a. Genes are intracellular factors for Plant growth is influenced by a variety growth. of external and internal factors. A brief b. Phytohormones are intracellular factors account of these factors is given below: for growth. Example: auxin, gibberellin, I. External Factors cytokinin. c. C/N ratio. a. Water Water is essential for cell enlargement The ratio of carbohydrates and nitrogenous as well as growth in the size of the compounds regulate the specific pattern cell. Turgidity of cells helps in growth of growth in plants. For example, if a plant extension. Water provides the medium for contains more nitrogenous compounds as enzymatic activities needed for growth. compared to carbohydrates it produces more protoplasm less mechanical tissues b. Nutrition and vigorous vegetative growth. On the Nutrition plays an important role in the other hand, less nitrogenous compounds formation of protoplasm. Macro and micro and more carbohydrates favour the elements are very important as sources of synthesis of more wall material, less energy. For example, carbon and oxygen protoplasm, and more mechanical tissues.

173 4. Measurement of growth 5. Sequence of developmental process in a plant cell Activity Development is a term that includes Measurement of growth by direct all the changes that an organism goes method. through during life cyle from germination Step 1: Take ordinary scale. of a seed to senescence. Diagrammatic Step 2: Measure ground stem up to representation of the sequence of processes the growing point of the plant. which constitute the development of a cell Step 3: Use Indian ink and mark at of a higher plant is given in the figure. It is regular intervals to measure the length also applicable to tissues/organ. of root, stem, and girth of the trunk.

Experiment: 1. Arc auxanometer: The increase in the length of the stem tip can easily be measured by an arc auxanometer which consists of a small pulley to the axis of which is attached a long pointer sliding over a graduated arc. A thread one end of which is tied to the stem tip and another end to a weight passes over the pulley tightly. As soon as the stem tip increases in length, the pulley moves and the pointer slide over the graduated arc (Figure 15.8). The reading is taken. The actual increase in the length of the stem is then calculated by knowing the length of the pointer and the radius of the pulley. If the radius of the pulley is 4 inches and the length of pointer 20 inches the actual growth is measured as follows: Arc

Pulley Pointer

Weight

Potted plant Stand

Figure 15.8: Arc auxanometer Actual growth in length 5 Distance travelled by the pointer × radius of the pulley Length of the pointer For example, actual growth in length 5 10 × 4 inches 20 inches 5 2 inches

174 1. Differentiation This ability is called plasticity. Example: The process of maturation of meristematic Heterophylly in cotton and coriander. cells to specific types of cells performing In such plants, the leaves of the juvenile specific functions is called differentiation. plant are different in shape from those in mature plants. On the other hand, 2. Dedifferentiation the difference in shapes of leaves The living differentiated cells which had produced in air and those produced in lost capacity to divide, regain the capacity water in buttercup also represent the to divide under certain conditions. Hence, heterophyllous development due to dedifferentiation is the regaining of the the environment. This phenomenon of ability of cell division by the differentiated heterophylly is an example of plasticity. cells. Example: Interfascicular cambium and Vascular cambium. 15.2 Plant Growth Regulators 3. Redifferentiation Plant Growth Regulators Differentiated cells, after multiplication (chemical messenger) again lose the ability to divide and mature are defined as organic to perform specific functions. This is called substances which are synthesized in minute redifferentiation (Figure 15.9). Example: Secondary xylem and Secondary phloem. quantities in one part of the plant body and transported to 4. Plasticity another part where they influence specific Plants follow different pathways in physiological processes. Five major groups response to environment or phases of of hormones viz., , gibberellins, life to form different kinds of structures. cytokinins, ethylene and abscisic acid are presently known to coordinate and regulate growth and development in plants. The term phytohormones is implied to those chemical substances which are synthesized by plants and thus, naturally occurring. On the other hand, there are several manufactured chemicals which often resemble the hormones in physiological action and even in molecular structure. Recently, another two groups, the brassinosteroids and polyamines were also known to behave like hormones.

1. Plant growth regulators – classification Plant Growth Regulators are classified Figure 15.9: Sequences of developmental process in a plant cell as natural and synthetic based on their

175 Plant Growth Regulators (PGRs)

Natural (Phytohormones) Synthetic

Plant Growth Promoters Growth inhibitors

Auxin Ethylene NAA Gibberellin Abscisic acid 2,4 -D Cytokinin 2,4,5 - T

Figure 15.10: Classification of Plant Growth Regulators source and a detailed flow diagram is ii. Antagonistic effects: The effect of two given in Figure 15.10. substances in such a way that they have opposite effects on the same process. 2. Characteristics of phytohormones One accelerates and other inhibits. i. Usually produced in tips of roots, stems Example: ABA and gibberellins during and leaves. seed or dormancy. ABA induces ii. Transfer of hormones from one place to dormancy and gibberellins break it. another takes part through conductive systems. 15.2.1 Auxins iii. They are required in trace quantities. 1. Discovery iv. All hormones are organic in nature. During 1880, Charles Darwin noted the v. There are no specialized cells or organs unilateral growth and curvature of Canary for their secretion. grass (Phalaris canariensis) coleoptile to light. vi. They are capable of influencing The term auxin (Greek: Auxin – to Grow) physiological activities leading to was first used by F. W. Went in 1926 using promotion, inhibition and modification Oats (Avena) coleoptile and isolated the of growth. auxin. F. W. Went in 1928 collected auxin in agar jelly. Kogl and Haugen Smith (1931) 3. Synergistic and Antagonistic effects isolated Auxin from human urine, and called i. Synergistic effects: The effect of one or it as Auxin A. Later on in 1934, similar active more substance in such a way that both substances was isolated from corn grain oil promote each others activity. Example: and was named as Auxin B. Kogl et al., (1934) Activity of auxin and gibberellins or found heteroauxin in the plant and chemically cytokinins. called it as Indole Acetic Acid (IAA)

176 Types of Auxin

Natural Synthetic Auxin occuring in plants are called These are synthesized artificially and have “Natural auxin” properties like Auxin. 1. Indole Acetic Acid (IAA) 1. 2,4-Dichloro Phenoxy Acetic Acid (2,4-D) 2. Indole Propionic Acid (IPA) 2. 2,4,5-Trichloro Phenoxy Acetic Acid (2,4,5-T) 3. Indole Butyric Acid (IBA) 3. Napthalene Acetic Acid (NAA) 4. Phenyl Acetic Acid (PAA)

Figure 15.11: Classification of Auxins

2. Occurrence 7. Chemical structure Auxin is generally produced by the growing Auxin has similar chemical structure of tips of the stem and root, from where they IAA. migrate to the region of the action. 8. Transport in Plants 3. Types of Auxin Auxin is polar in transport. It includes Auxins are divided into two categories basipetal and acropetal transport. Natural auxins and Synthetic auxins Basipetal means transport through (Figure 15.11). phloem from shoot to root and acropetal means transport through xylem from root Anti-auxins to shoot. Anti-auxin compounds when applied to the plant inhibit the effect of auxin. 9. Bioassay (Avena Curvature Test / Example: 2, 4, 5-Tri Iodine Benzoic Went Experiment) Acid (TIBA) and Napthylpthalamine. Bioassay means testing of substances for their activity in causing a growth response in a living plant or its part. 4. Free auxin They move out of tissues as they are easily The procedure involves the following diffusible. Example: IAA. steps:

5. Bound Auxin When the Avena seedlings have attained They are not diffusible. Example: IAA- a height of 15 to 30 mm, about 1mm of Aspartic acid the coleoptile tip is removed. This apical part is the source of natural auxin. The 6. Precursor tip is now placed on agar blocks for few The amino acid Tryptophan is the hours. During this period, the auxin precursor of IAA and zinc is required for diffuses out of these tips into the agar. its synthesis. The auxin containing agar block is now

177 Auxin in the Auxin containing agar block Diffusion of Auxin Avena coleoptile in one side of stump from agar block Decapited stump

Coleoptile placed on Agar Block Auxin diffuses in to agar block

Figure 15.12: Avena Curvature Test placed on one side of the decapitated and for the formation of callus. stump of Avena coleoptile. The auxin • Auxin stimulates respiration. from the agar blocks diffuses down • Auxin induces vascular differentiation. through coleoptile along the side to which the auxin agar block is placed. An agar block without auxin is placed on Agent Orange another decapitated coleoptile. Within Mixture of two phenoxy herbicides an hour, the coleoptiles with auxin agar 2,4-D and 2,4,5-T is given the name block bends on the opposite side where ‘Agent orange’ which was used by the agar block is placed. This curvature USA in Vietnam war for defoliation can be measured (Figure 15.12). of forest (chemical warfare).

10. Physiological Effects • They promote cell elongation in stem and coleoptile. • At higher concentrations auxins inhibit the elongation of roots but induce more lateral roots. Promotes growth of root only at extremely low concentrations. • Suppression of growth in lateral bud by apical bud due to auxin produced by apical bud is termed as In botanical gardens and tea gardens, . apical dominance gardeners trim the plants regularly • Auxin prevents abscission. so that they remain bushy. Does this • It is responsible for initiation and practice have any scientific explanation? promotion of cell division in cambium, Yes, trimming of plants removes which is responsible for the secondary apical buds and hence apical growth and tumor. This property of dominance. The lateral buds sprout induction of cell division has been and make the plants bushy. exploited for techniques

178 11. Agricultural role and steroids) formed by 5-C precursor, • It is used to eradicate weeds. Example: an Isoprenoid unit called Iso Pentenyl 2,4-D and 2,4,5-T. Pyrophosphate (IPP) through a number • Synthetic auxins are used in the formation of intermediates. The primary precursor of seedless fruits (Parthenocarpic fruit). is acetate. • It is used to break the dormancy in seeds. 4. Chemical structure • Induce flowering in Pineapple by NAA All gibberellins have gibbane ring & 2,4-D. structure. • Increase the number of female flowers and fruits in cucurbits. 5. Transport in plants The transport of gibberellins in plants is 15.2.2 Gibberellins non-polar. Gibberellins are translocated through phloem and also occur in xylem 1. Discovery due to lateral movement between vascular The effect of gibberellins had been known bundles. in Japan since early 1800 where certain rice plants were found to suffer from 6. Bioassay (Dwarf Pea assay) ‘Bakanae’ or foolish seedling disease. Seeds of dwarf pea are allowed to germinate This disease was found by Kurosawa till the formation of the coleoptile. GA (1926) to be caused by a fungus Gibberella solution is applied to some seedlings. Others fujikuroi. The active substance was are kept under control. Epicotyle length separated from fungus and named as is measured and as such, GA stimulating gibberellin by Yabuta (1935). These are epicotyle growth can be seen. more than 100 gibberellins reported from both fungi and higher plants. They are 7. Physiological Effects • It produces extraordinary elongation noted as GA1, GA2, GA3 and so on. GA3 is the first discovered gibberellin. In 1938, of stem caused by cell division and cell elongation. Yabuta and Sumiki isolated gibberellin in crystalline form. In1955, et al., gave • plants (genetic dwarfism) the name gibberellic acid. In 1961, Cross plants exhibit excessive internodal et al., established its structure. growth when they are treated with gibberellins. This sudden elongation 2. Occurrence of stem followed by flowering is called The major site of gibberellin production bolting (Figure 15.13). in plants is parts like embryo, roots and • Gibberellin breaks dormancy in potato young leaves near the tip. Immature seeds tubers. are rich in gibberellins. • Many biennials usually flower during second year of their growth. For 3. Precursors flowering to take place, these plants The gibberellins are chemically related to should be exposed to cold season. Such terpenoids (natural rubber, carotenoids plants could be made to flower without

179 (liquid endosperm of coconut) which contains cell division inducing substances. In 1954, Skoog and Miller discovered that autoclaved DNA from herring sperm stimulated cell division in tobacco Rosette leaves pith cells. They called this cell division inducing principle as kinetin (chemical structure: 6-Furfuryl Amino Acid). (b) Treated plant This does not occur in plants. In 1963, (a) Untreated plant showing bolting. Lethan introduced the term cytokinin. Figure 15.13: Bolting In 1964, Lethan and Miller isolated and identified a new cytokinin called exposure to cold season in the first Zeatin from unripe grains of maize. The most year itself, when they are treated with widely occurring cytokinin in plants is gibberellins. Iso Pentenyl adenine (IPA). 8. Agricultural role 2. Occurrence • Formation of seedless fruits without Cytokinin is formed in root apex, shoot fertilization is induced by gibberellins apex, buds and young fruits. Example: Seedless tomato, apple and cucumber. 3. Precursor • It promotes the formation of male Cytokinins are derivatives of the purine flowers in cuccurbitaceae. It helps in adenine. crop improvement. • Uniform bolting and increased uniform 4. Bioassay (Neem Assay) seed production. Neem are measured and placed in cytokinin solution as well as in ordinary • Improves number and size of fruits in water. Enlargement of cotyledons is an grapes. It increase yield. indication of cytokinin activity. • Promotes elongation of inter-node in sugarcane without decreasing sugar 5. Transport in plants content. The distribution of cytokinin in plants • Promotion of flowering in long day is not as wide as those of auxin and plants even under short day conditions. gibberellins but found mostly in roots. • It stimulates the seed germination. Cytokinins appear to be translocated through xylem. 15.2.3 Cytokinins (Cytos – cell, 6. Physiological effect Kinesis – division) • Cytokinin promotes cell division in the 1. Discovery presence of auxin (IAA). The presence of cell division inducing • Induces cell enlargement associated substances in plants was first demonstrated with IAA and gibberellins by Haberlandt in 1913 in Coconut milk

180 • Cytokinin can break the dormancy 4. Precursor of certain light-sensitive seeds like It is a derivative of amino acid methionine, tobacco and induces seed germination. linolenic acid and fumaric acid. • Cytokinin promotes the growth of lateral bud in the presence of apical bud. 5. Bioassay (Gas Chromatography) Ethylene can be measured by gas • Application of cytokinin delays the chromatography. This technique helps in process of aging by nutrient mobilization. the detection of exact amount of ethylene It is known as . Richmond Lang effect from different plant tissues like lemon • Cytokinin (i) increases rate protein and orange. synthesis (ii) induces the formation of inter-fascicular cambium 6. Physiological Effects (iii) overcomes apical dominance • Ethylene stimulates respiration and (iv) induces formation of new leaves, ripening in fruits. chloroplast and lateral shoots. • It stimulates radial growth in stem and • Plants accumulate solutes very actively root and inhibits linear growth. with the help of cytokinins. • It breaks the dormancy of buds, seeds and storage organs. 15.2.4 Ethylene • It stimulates formation of abscission (Gaseous Phytohormone) zone in leaves, flowers and fruits. This makes the leaves to shed prematurely. Almost all plant tissues produce ethylene • Inhibition of stem elongation gas in minute quantities. (shortening the internode). 1. Discovery • In low concentration, ethylene helps in root initiation. In 1924, Denny found that ethylene stimulates • Growth of lateral roots and root hairs. the ripening of lemons. In 1934, R. Gane found that ripe bananas contain abundant This increases the absorption surface of the plant roots. ethylene. In 1935, Cocken et al., identified ethylene as a natural . • The growth of fruits is stimulated by ethylene in some plants. It is more 2. Occurrence marked in climacteric fruits. Maximum synthesis occurs during • Ethylene causes epinasty. climacteric ripening of fruits (see Box info) and tissues undergoing senescence. Agricultural role It is formed in almost all plant parts like • Ethylene normally reduces flowering in roots, leaves, flowers, fruits and seeds. plants except in Pine apple and Mango. • It increases the number of female 3. Transport in plants flowers and decreases the number of Ethylene can easily diffuse inside the plant male flowers. through intercellular spaces. • Ethylene spray in cucumber crop produces female flowers and increases the yield.

181 GROWTH PROMOTERS x X Weedicide growth Promote lateral bud 3 Bolting 6 12 X Prevents 9 Auxin abscission ageing process Delaying x Gibberellins Apical Cytokinins dominance Callus Root /Shoot initiation from 3 A 3 Breaks seed dormancy G A B seed A Regulators Plant growth Induces Plant Growth dormancy Auxin, GA and Cytokinin induces Synergistic effects Antagonistic effects

ABA

ABA stomata Closure of Fruit ripening Induce ABA Ethylene Abscission Radial growth

Ethylene Induce

of leaf Abscission Yellowing Yellowing GROWTH INHIBITORS GROWTH

182 3. Precursors Climacteric fruits: In most of the The hormone is formed from mevalonic plants, there is sharp rise in respiration acid pathway or xanthophylls. rate near the end of the development of fruit, called climacteric rise. Such 4. Transport in plants fruits are called climacteric fruits. The Abscisic acid is transported to all parts ripening on demand can be induced of the plant through diffusion as well as in these fruits by exposing them to through phloem and xylem. normal air containing about 1 ppm of ethylene. A liquid called ethephon 5. Chemical structure is being used in fruit ripening as it It has carotenoid structure. continuously releases ethylene. 6. Bioassay (Rice Coleoptile) Example: Tomato, , Banana, The inhibition of IAA induces straight Mango. growth of rice seedling coleoptiles. Non climacteric fruits: All fruits cannot be ripened by exposure to 7. Physiological effects ethylene. Such fruits are called non- • It helps in reducing transpiration rate climacteric fruits and are insensitive by closing stomata. It inhibits K1 uptake to ethylene. by guard cells and promotes the leakage of malic acid. It results in closure of Example: Grapes, Watermelon, stomata. Orange. • It spoils chlorophylls, proteins and nucleic acids of leaves making them 15.2.5 Abscisic Acid (ABA) yellow. (Stress Phyto Hormone) • Inhibition of cell division and cell elongation. 1. Discovery In 1963, the hormone was first isolated • ABA is a powerful growth inhibitor. It causes 50% inhibition of growth in Oat by Addicott et al., from young cotton coleoptile. bolls and named as Abscission II. Eagles and Wareing during 1963–64 isolated a • It induces bud and seed dormancy. dormancy inducing substance from leaves • It promotes the abscission of leaves, of Betula and called it as dormin. In 1965, flowers and fruits by forming abscission it was found by Cornsforth et al., that both layers. dormin and abscission are chemically • ABA plays an important role in plants same compounds and called Abscisic during water stress and during drought Acid (ABA). conditions. It results in loss of turgor and closure of stomata. 2. Occurrence This hormone is found abundantly inside • It has anti-auxin and anti-gibberellin the chloroplast of green cells. property. • Abscisic acid promotes senescence in

183 leaves by causing loss of chlorophyll 15.3 Plant Movements pigment decreasing the rate of Plants have the capacity for photosynthesis and changing the rate changing their positions of proteins and nucleic acid synthesis. in response to external 8. Agricultural Role or internal stimuli, which are known as • In Cannabis sativa, induces male flower plant formation on female plants. movements. Movements are basically of two types: I. Vital movements • Induction of flowers in short day plants. and II. Physical movements (hygroscopic) • It promotes sprouting in storage organs (Figure 15.14). like Potato. • ABA plays an important role in plants I. Vital movements during water stress drought conditions. Vital movements are those which are • It inhibits the shoot growth and exhibited by the living cells or plants or promotes growth of root system. This organs and they are always related to character protect the plants from water the irritability of the protoplasm. These stress. Hence, ABA is called as stress movements are of two types: hormone. A. Movements of locomotion B. Movements of curvature

Plant Movement

Vital Movement Physical Movement

Movement of locomotion Movement of curvature

Autonomic Paratonic Autonomic Paratonic (Spontaneous) (Tactic/ Induced) (Spontaneous) (Tactic/ Induced)

Ciliary Phototactic Amoeboid Chemotactic Cyclosis Thermotactic Tropic Nastic (Growth Movement) (Variation Movement) Geotropic Nyctinastic Phototropic Seismonastic Thigmotropic Thigmonastic Growth Movement Variation Movement Hydrotropic Hyponastic Chemotropic Epinastic Thermotropic Nutational Aerotropic

Figure 15.14: Types of Plant Movements

184 Paratonic or Tactic (induced) movement of locomotion

Phototactic Chemotactic Thermotactic These movements It occurs in response to It occurs in response occur in response to chemical . to heat stimulus. light. Example: Antherozoids in Example: Example: Zoospores Bryophytes and Chlamydomonas of Chlamydomonas Pteridophytes are moves from cold to warm water attracted to chemical substances of Archegonia

Figure 15.15: Types of Paratonic movements A. Movements of locomotion i. Autonomic movements of curvature These movements include the movement The movement arising from internal of protoplasm inside the cell or movement changes or internal stimuli of plant of whole unicellular or multicellular plant body is called autonomic movement body as in Chlamydomonas, gametes and of curvature. This does not require any zoospores. external stimulus. They are two types: a. It is of i. Autonomic movements of locomotion Autonomic movement of growth: the following types: The movements arising from internal changes or internal stimuli of plant 1. Hyponasty: When growth is more on lower surface, show curvature body is called autonomic movements of locomotion. This movement takes place on upper side and ultimately the flower due to the presence of cilia or flagella and becomes closed. Such type of movement movement of cytoplasm (Cyclosis). is called hyponasty. 2. Epinasty: When the growth is more ii. Paratonic or Tactic (induced) on upper surface, petals show curvature movements of locomotion on the lower side and ultimately the The movements due to external factors flower opens. Such movement is called or stimuli like light, temperature and epinasty. The flower usually opens at chemicals are called paratonic movement high temperature and remains closed at of locomotion (Figure 15.15). low temperature (Figure 15.16). B. Movement of curvature 3. Nutation: The growth of the stem In higher plants they are restricted only apices occurs in a zig-zag manner. It is to bending or curvature of some of their because the two sides of the stem apex parts. There are mainly two types: alternatively grow more. Such growth movements are called as nutational They are i) Autonomic movement of movements. In some plants nutational curvature and ii) Paratonic movement of movements allow the shoots apex curvature. to grow in helical path in upward

185 Hyponasty Epinasty

Figure 15.16: Hyponasty and Epinasty

direction. This movement is called circumnutation. It is commonly found in the stems of climbers of Cucurbitaceae (Figure 15. 17). b. Autonomic Movement of variation: It happens in Indian telegraph plant. (Desmodium gyrans). The compound leaf consists of a larger terminal and two smaller lateral leaflets. During day time, the two lateral leaflets move upward at an angle of 90° and come to lie parallel to the rachis. Again, they may move downward at 180° so that they are Circumnutation parallel to the rachis. They may again Figure 15.17: move upward at 90° to come in their original position. All these movements occur with jerks after intervals, each movement being completed in about 2 minutes (Figure 15.18). ii. Paratonic (induces) movements of curvature The movement arising from external stimulus is called Paratonic (Induced) movements of curvature. They are of two types. 1) Tropic movements 2) Nastic movements (Table 2) a. Tropic movements A movement that occurs in response to Figure 15.18: Autonomic Movement of an unidirectional stimulus is called tropic Variation

186 Table 2: Differences between Tropic Movements and Nastic movements Tropic Movements Nastic movements 1. Movement occurs due to unidirectional These movements occur due to a stimulus. diffused stimulus. 2. The stimulus acts on protoplasm from one The stimulus acts on the protoplasm direction only. from all sides. 3. The response is directly related to the The response has no relation to the direction of the stimulus. direction of the stimulus but with organ. 4. These are movements of curvature caused These are also the movement of by unilateral growth. curvature but they are caused by reversible turgor changes. 5. Tropic movements may be phototropic, Nastic movements may be geotropic, hydrotropic, thigmotropic, seismonastic, photonastic or chemotropic, thermotropic or aerotropic. thermonastic movement or tropism. There are seven flowers move towards the stimulus of light types in tropic movements (Geotropic, and are said to be positively phototropic Phototropic, Thigmotropic, Chemotropic, while others such as roots and Hydrotropic, Thermotropic and Aerotropic) which move away from the stimulus of 1. Geotropism light are called negatively phototropic. The movements which take place in b. Nastic Movements response to gravity stimulus are called When growth movements occur in . The primary geotropic movements response to an external stimulus which is roots growing down into soil are not unidirectional but diffused, they are Primary stems that positive geotropic. called nastic or paratonic movements of grow away from soil (against gravity) variation. Paratonic variation movements are . Secondary roots negative geotropic are determined by some external stimuli, growing at right angles to the force of light, temperature, chemicals and touch. gravity are . Secondary Diageotropic They are: lateral roots which grow obliquely downwards are Plagiogeotropic. 1. Nyctinastic movement (or) sleep Lateral roots and branches which are movement not sensitive to gravitational stimulus The diurnal (change in day-night) are . Apogeotropic movements of leaves and flowers of some 2. Phototropism species which take up sleep position at The tropic movement taking place as night are called nyctinastic movements. a response to light stimulus is called They are caused by relative changes in phototropism. Some of the plant parts such cell size on the opposite sides of the leaf as stems, branches, leaves and pedicels of base called pulvinus. The movements

187 are attributed to the amount of auxin and Experiment to demonstrate K1 ions. The entry of water to the lower negative geotropism in aerial stem side of the pulvinus causes the leaves to The Clinostat has a rotating pot like container mounted on an axis rod. stand erect and exit of water causes them A potted plant is fitted horizontally to drop. They are of two types: on the Clinostat and rotated slowly which completely eliminates gravity i. Photonasty as all the sides of the plant are equally The nastic movement caused in response to stimulated. If the rotation of the light is called or Clinostat is stopped for a considerable photonasty photonastic period of time then the tip of the movement. The opening of leaves and stem is observed to curve and grow flowers during daytime and their close at upwards this proves that the stem tip night is an example. is negatively geotropic (Figure 15.19). ii. Thermonasty Clinostat The nastic movement taking place in response to temperature is called thermonasty or thermonastic movement. In Crocus the flowers open at high temperature and close at low temperature.

Figure 15.19: Clinostat 2. Seismonastic movement This means a response to shaking. The Experiment to demonstrate positive best example is Mimosa pudica (Touch- phototropism in shoot tips A darkened black box is taken having a small window on one side. A well- watered potted plant is placed inside the box. This is referred to as a phototropic chamber or heliotropic chamber. If the window is kept closed for about 24 hours the plant shows normal growth. If the window is kept opened, it is found after two days that the shoot tip bends and grows towards light proving that it is positively phototropic (Figure 15.20). Figure 15.21: Mimosa pudica showing

Closed Window Open Window response to touch

Direction of Darkness Light me-not plant) which is a sensitive plant (Figure 15.21). Such plants respond to stimuli such as touch, blow or metallic by folding their leaflets and lowering their leaves .This effect is caused by the movement of water in and out of Figure15.20: Experiment to demonstrate the parenchymatous cells of the pulvinus Photropism (Figure 15.22).

188 b c

(d) (e) plasma membrane H2O cell wall flexor cells 2+ turgid extensor Ca cells TnV O N H 2 pulvinus H + K+ Cl- turgid state

shrinking swelling - + Cl stretched K flaccid state flexor cells H+

H O H2O flaccid extensor 2 H2O O cells H 2 H O H2O 2 TnVT N

Figure 15.22: Mechanism of Seismonastic movement in Mimosa pudica 3. Thigmonastic movement hairs are activated. Similarly, in dionaea, The movements found in the leaves of the two halves of the leaf curve upwards Drosera and Dionaea (Venus fly trap) result along the midrib. These parts of the leaves in response to the touch stimulus of insects. come to their normal position after the As soon as an insect sits on the leaf the cilia insect has been digested (Figure 15.23). curve inward to trap the insect and trigger II Physical Movement (Hygroscopic Movements) Physical movements are those which are found in dead parts of the plants and they are not related to any irritability of the protoplasm. They are also called hygroscopic movements or mechanical movements. Dispersal of and seeds, dehiscence of sporangia, bursting of seeds and movement of elaters are the examples of physical or hygroscopic Figure 15.23: in Dionaea movement.

189 15.4 Photoperiodism Intermediate plants Day neutral plants Trees take several years for initiation of flowering whereas an annual herb flowers within few months. Each plant requires Photoperiodism in plants a specific time period to complete their vegetative phase which will be followed by reproductive phase as per their Long day plants Short day plants internal control points through Biological Clock. The physiological mechanisms in relation to flowering are controlled by Short long day Long short day (i) light period (Photoperiodism) and plants plants (ii) temperature (Vernalization). The Figure: 15.24 Classification of Plants based physiological change on flowering due on Photoperiodism to relative length of light and darkness iii. : The plants that require (photoperiod) is called . Short day plants Photoperiodism a short critical day length for flowering The term photoperiodism was coined are called short day plants or long night by and (1920) when they Garner Allard plants. Example: Tobacco, Cocklebur, observed this in ‘Biloxi’ variety of soybean Soybean, Rice and Chrysanthemum. (Glycine max) and ‘Maryland mammoth’ iv. : These are variety of tobacco (Nicotiana tabacum). Long short day plants The photoperiod required to induce actually short-day plants but they have to be exposed to long days during their flowering is called critical day length. Maryland mammoth (tobacco variety) early periods of growth for flowering. requires 12 hours of light and cocklebur Example: Some species of Bryophyllum and Night jasmine. (Xanthium pensylvanicum) requires 15.05 hours of light for flowering. v. Intermediate day plants: These require a photoperiod between long day and 1. Classification of plants based on short day for flowering. Example: Photoperiodism Sugarcane and Coleus. Depending upon the photoperiodic vi. Day neutral plants: There are a responses plants are classified as given in number of plants which can flower in Figure 15.24. all possible photoperiods. They are also i. Long day plants: The plants that require called photo neutrals or indeterminate long critical day length for flowering plants. Example: Potato, Rhododendron, are called long day plants or short night Tomato and Cotton. plants. Example: Pea, Barley and Oats. 2. Photoperiodic induction ii. Short long day plants: These are long day plants but should be exposed to An appropriate photoperiod in 24 hours’ short day lengths during early period of cycle constitutes one inductive cycle. Plants may require one or more inductive growth for flowering. Example: Wheat and Rye. cycles for flowering. The phenomenon of

190 conversion of leaf primordia into flower 5. Phytochrome primordia under the influence of suitable inductive cycles is called X photoperiodic Day . Example: (SDP) – 1 660nm induction Xanthium P P P X Physiological response r 730nm fr fr inductive cycle and Plantago (LDP) – 25 Night inductive cycles. Phytochrome is a bluish biliprotein pigment 3. Site of Photoinductive perception responsible for the perception of light in Photoperiodic stimulus is perceived by the photo physiological process. Butler et al., leaves. Floral hormone is synthesised in (1959) named this pigment and it exists leaves and translocated to the apical tip to in two interconvertible forms: (i) red light promote flowering. This can be explained absorbing pigment which is designated as by a simple experiment on Cocklebur Pr and (ii) far red light absorbing pigment which is designated as P . The P form (Xanthium pensylvanicum), a short day fr r absorbs red light in 660nm and changes to P plant. Usually Xanthium will flower under fr. short day conditions. If the plant is defoliated The frP form absorbs far red light in 730nm and kept under short day conditions it will and changes to Pr. The rP form is biologically not flower. Flowering will occur even when inactive and it is stable whereas Pfr form is all the leaves are removed except one leaf. biologically active and it is very unstable. In If a cocklebur plant is defoliated and kept short day plants, Pr promotes flowering and under long day conditions, it will not flower. Pfr inhibits the flowering whereas in long If one of its leaves is exposed to short day day plants flowering is promoted by frP and condition and rest are in long day condition, inhibited by Pr form. Pfr is always associated flowering will occur (Figure 15.25). with hydrophobic area of membrane systems while Pr is found in diffused state in the The nature of flower producing cytoplasm. The interconversion of the two stimulus has been elusive so far. It is forms of phytochrome is mainly involved in believed by many physiologists that it flower induction and also additionally plays is a hormone called florigen. The term a role in seed germination and changes in florigen was coined by Chailakyan membrane conformation. (1936) but it is not possible to isolate. Short Day Long Day

4. Importance of photoperiodism Short 1. The knowledge of photoperiodism Day plays an important role in hybridisation experiments. 2. Photoperiodism is an excellent example of physiological pre-conditioning that is using an external factor to induce ABCDEF physiological changes in the plant. Figure 15.25: Experiment on Cocklebur plant showing photoperiodic stimulus

191 192 15.5 Vernalization (Vernal – Spring

Like) C Devernalization

High Besides photoperiod certain plants require temperature a low temperature exposure in their B Vernalin D Chilling earlier stages for flowering. Many species Translocation of flower A inducing substance of biennials and perennials are induced to Florigen F o flower by low temperature exposure (0 C to Precursor 5oC). This process is called Vernalization. The term Vernalization was first used by T. D. Lysenko (1938).

1. Mechanism of Vernalization: Figure 15.26: Vernalization and Flowering Two main theories to explain the seeds are transferred to low temperature mechanism of vernalization are: (3oC to 5oC) from few days to 30 days. i. Hypothesis of phasic development Germinated seeds after this treatment are ii. Hypothesis of hormonal involvement allowed to dry and then sown. The plants will show quick flowering when compared i. Hypothesis of phasic development to untreated control plants. According to Lysenko, development of an annual seed plant consists of two phases. 3. Devernalization First phase is thermostage, which is Reversal of the effect of vernalization is vegetative phase requiring low temperature called devernalization. and suitable moisture. Next phase is photo 4. Practical applications which requires high temperature for stage 1. Vernalization shortens the vegetative synthesis of florigen (flowering hormone). period and induces the plant to ii. Hypothesis of hormonal involvement flower earlier. According to Purvis (1961), formation 2. It increases the cold resistance of the of a substance A from its precursor, plants. is converted into B after chilling. The 3. It increases the resistance of plants to substance B is unstable. At suitable fungal disease. temperature B is converted into stable 4. Plant breeding can be accelerated. compound D called Vernalin. Vernalin is converted to F (Florigen). Florigen induces 15.6 Seed Germination and Dormancy flower formation. At high temperature B is converted to C and devernalization occurs I. Seed Germination (Figure 15.26). The activation and growth of embryo from seed into seedling during favourable 2. Technique of Vernalization: conditions is called seed germination. The seeds are first soaked in water and allowed to germinate at 10o C to 12o C. Then

193 but some seeds do not germinate when due to blockage by cork cells. These suitable conditions like water, oxygen and seeds are shaken vigorously to remove favourable temperature are not available. the plug which is called Impaction. Germination of such seeds may be delayed iii. Stratification: Seeds of rosaceous for days, months or years. The condition plants (Apple, , Peach and ) of a seed when it fails to germinate even in will not germinate until they have been suitable environmental condition is called exposed to well aerated, moist condition seed dormancy. There are two main under low temperature (0oC to 10oC) reasons for the development of dormancy: for weeks to months. Such treatment is Imposed dormancy and innate dormancy. called Stratification. Imposed dormancy is due to low moisture iv. Alternating temperatures: Germination and low temperature. Innate dormancy is of some seeds is strongly promoted related to the properties of seed itself. by alternating daily temperatures. An alternation of low and high temperature 1. Factors causing dormancy of seeds: improves the germination of seeds. i. Hard, tough seed coat causes barrier v. : The dormancy of photoblastic effect as impermeability of water, gas Light seeds can be broken by exposing them and restriction of the expansion of to red light. embryo prevents seed germination. ii. Many species of seeds produce 15.7 Senescence imperfectly developed called Plant life comprises some sequential events, rudimentary embryos which promotes : germination, juvenile stage, maturation, dormancy. viz old age and death. Old age is called iii. Lack of specific light requirement leads in plants. Senescence refers to to seed dormancy. senescence all collective, progressive and deteriorative iv. A range of temperatures either higher processes which ultimately lead to complete or lower cause dormancy. loss of organization and function. Unlike v. The presence of inhibitors like phenolic animals, plants continuously form new compounds which inhibits seed organs and older organs undergo a highly germination cause dormancy. regulated senescence program to maximize nutrient export. 2. Methods of breaking dormancy: The dormancy of seeds can be broken by 1. Types of Senescence different methods. These are: Leopold (1961) has recognised four types of senescence: i. Scarification: Mechanical and chemical treatments like cutting or chipping of i. Overall senescence hard tough seed coat and use of organic ii. Top senescence solvents to remove waxy or fatty iii. Deciduous senescence compounds are called as Scarification. iv. Progressive senescence ii. Impaction: In some seeds water and oxygen are unable to penetrate micropyle

195 secretes hydrolytic enzymes. The branch of botany which deals with • The starch content is decreased in the ageing, abscission and senescence is cells. called Phytogerontology • Photosynthesis is reduced due to loss of chlorophyll accompanied by synthesis i. Overall senescence: This kind of senescence occurs in annual plants and accumulation of anthocyanin when entire plant gets affected and dies. pigments, therefore the leaf becomes red. Example: Wheat and Soybean. It also • There is a marked decrease in protein occurs in few perennials also. Example: content in the senescing organ. Agave and Bamboo. • RNA content of the leaf particularly ii. Top senescence: It occurs in aerial parts rRNA level is decreased in the cells of plants. It is common in perennials, due to increased activity of the enzyme underground and root system remains RNAase. viable. Example: Banana and Gladiolus. • DNA molecules in senescencing leaves iii. Deciduous senescence: It is common degenerate by the increased activity of in deciduous plants and occurs only in enzyme DNAase. leaves of plants, bulk of the stem and 3. Factors affecting Senescence: root system remains alive. Example: • ABA and ethylene accelerate senescence Elm and Maple. while auxin and cytokinin retard iv. : This kind of Progressive senescence senescence. senescence is gradual. First it occurs • Nitrogen deficiency increases in old leaves followed by new leaves senescence whereas nitrogen supply then stem and finally root system. It is retards senescence. common in annuals (Figure 15.28). • High temperature accelerates senescence 2. Physiology of Senescence but low temperature retards senescence. • Cells undergo changes in structure. • Senescence is rapid in dark than in • Vacuole of the cell acts as lysosome and light.

Overall senescence Top senescence Deciduous senescence Progressive senescence

Figure 15.28: Different types of senescence in plants

196 • Water stress leads to accumulation of its vascular system to prevent loss of water ABA leading to senescence. and nutrients. Final stage of senescence is abscission. In temperate regions all the 4. Programmed cell death (PCD) leaves of deciduous plants fall in autumn Senescence is controlled by plants own and give rise to naked appearance, then the genetic programme and death of the plant new leaves are developed in the subsequent or plant part consequent to senescence is spring season. But in evergreen plants there called Programmed Cell Death. In short is gradual abscission of leaves, the older senescence of an individual cell is called PCD. leaves fall while new leaves are developed The proteolytic enzymes involving PCD continuously throughout the year. in plants are phytaspases and in animals are caspases. The nutrients and other 6. Morphological and Anatomical substrates from senescing cells and tissues changes during abscission are remobilized and reallocated to other parts Leaf abscission takes place at the base of of the plant that survives. The protoplasts petiole which is marked internally by a of developing xylem vessels and tracheids distinct zone of few layers of thin walled die and disappear at maturity to make them cells arranged transversely. This zone is functionally efficient to conduct water for called . transport. In aquatic plants, aerenchyma abscission zone or abscission layer An abscission layer is greenish-grey in is normally formed in different parts of the colour and is formed by rows of cells of 2 to plant such as roots and stems which encloses large air spaces that are created through PCD. 15 cells thick. The cells of abscission layer In the development of unisexual flowers, separate due to dissolution of middle lamella male and female flowers are present in earlier and primary wall of cells by the activity of stages, but only one of these two completes enzymes pectinase and cellulase resulting its development while other aborts through in loosening of cells. Tyloses are also formed PCD (Figure 15.29). blocking the conducting vessels. Degrading of chlorophyll occur leading to the change 5. Abscission in the colour of leaves, leaf detachment Abscission is a physiological process of from the plant and leaf fall. After abscission, shedding of organs like leaves, flowers, fruits outer layer of cells becomes suberized by the and seeds from the parent plant body. When development of periderm (Figure 15.30). these parts are removed the plant seals off

Mitochondria Vacuole Nucleus

Plastid

Figure 15.29: Programmed cell death

197 functioning of plants under adverse environmental conditions is called Pholoem stress Xylem physiology. Jacob Levitt (1972) first used the term biological stress in relation to plants and according to him stress is “any change in environmental condition that might adversely change the growth and Cortex development of a plant”. Abscission layer The reaction of plants facing stress is called strain. For example, if a normal plant growing under favourable light conditions is subjected to low light intensity, its photosynthesis is reduced. Thus, low light intensity is referred as stress and reduction of photosynthesis is referred as strain. Biological strains are of Figure 15.30: L.S of petiolar base showing two types; Elastic biological strain and Plastic abscission layer biological strain. If the reaction of plant function is temporary and when it returns to 7. Hormones influencing abscission its original state it is called elastic biological All naturally occurring hormones strain. Example: Temporary wilting. If influence the process of abscission. Auxins the reaction is permanent and the plant and cytokinins retard abscission, while function does not return to the normal state abscisic acid (ABA) and ethylene induce it. it is called plastic biological strain. Example: Permanent wilting. Some plants get adapted 8. Significance of abscission to stress condition and are not adversely 1. Abscission separates dead parts of the affected by stress. Such plants are called plant, like old leaves and ripe fruits. stress resistant or stress tolerant plants. 2. It helps in dispersal of fruits and Example: Mangroves. Some plants cannot continuing the life cycle of the plant. face stress and they pass their adverse period 3. Abscission of leaves in deciduous in dormant state and so they are called stress plants helps in water conservation enduring plants. Ephemeral plants are short during summer. lived desert plants, which complete their life 4. In lower plants, shedding of vegetative cycle during the seasonal rains before the parts like gemmae or plantlets help in onset of dry season. These ephemeral plants vegetative . are called stress escapers. Stress in plants can be classified as given in figure 15.31. 15.8 Stress Physiology 1. Biotic Stresses Like all other organisms, plants are also These are adverse effects on plants caused subjected to various environmental stresses by other living organisms such as viruses, such as water deficit, drought, cold, heat, bacteria, fungi, parasites, insects, weeds and salinity and air pollution. The study of

198 Environmental Stress

Positive Allelopathy Allelopathic plant Biotic Abiotic Negative Allelopathy Allelopathy Pathogenecity Atmospheric Edaphic

Water Salt Promote Retard Light Temperature Air pollution growth growth Figure 15.31: Classification of Stress types Allelochemicals in plants SOIL Figure 15.32: Allelopathy in plants competing plants. Biotic environmental stress is also caused due to the activity of man by allelochemicals exhibit symptoms such as cutting herbs and trees, twigs for fodders, fuels wilting, chlorosis and death. and agricultural purposes. The biotic stresses caused by bacteria, fungi and nematodes that Check your grasp! Are all plants are ever present in the environment are called allelopathic? Can allelopathic potential biotic stresses. These are divided into chemicals affect animals and humans? two types. They are: i) Allelopathy Tree of heaven (Ailanthus altissima) is An organism producing one or more a recent addition to the list of allelopathic biochemical substances that greatly trees. Ailanthone an allelochemical influence the germination, growth and extracted from the root of Ailanthus acts reproduction of other organisms is as potent herbicide. In Sorghum plant the allelochemical sorgolone possess called Allelopathy. These biochemicals allelopathic activity. It is found in root are known as allelochemicals. They are beneficial (positive allelopathic) exudates of most Sorghum species. Root or detrimental (negative allelopathic). exudation of maize inhibits the growth of These allelochemicals are obtained from some weeds such as Chenopodium album leaf after leaching on the ground and and Amaranthus retroflexus. The seed also from roots. The term allelopathy is exudates of oat (Avena fatua) affect the germination of wheat seedling. from Greek words allelon-each other and -to suffer and first used in 1937 by pathos ii. Pathogenecity . Allelopathic effect may Hans Molisch The effect of microbes that cause diseases occur with weeds on crops and vice versa in plants. Example: (Figure 15.32). Xanthomonas citri One of the most famous allelopathic 2. Abiotic Stresses plants is Black walnut (Juglans nigrum). The Abiotic stress may occur due to an chemical which is present in Black walnut atmospheric condition (atmospheric is Juglone and it is a respiratory inhibitor. stress) or soil condition (edaphic stress). Solanaceous plants such as tomato, Atmospheric stresses may occur due capsicum and eggplant are susceptible to to excess and deficient levels of light juglone. These plants when exposed to these temperature and air pollutants.

199 i. Light Stress b. Low Temperature Light limits the distribution of species. Low temperature stress is quite harmful to In low light intensity Sciophytes (shade plants and the temperature near freezing loving plants) develop, while in high light point causes irreversible damage so that the plants fail to survive under extreme intensity Heliophytes (high light loving plants) develop. In low light intensity, cold conditions. However, some plants stomata do not fully open hence there is growing in alpine and arctic regions can survive under low temperature and such less diffusion of gases. As a result, there plants are said to be . Stress is less photosynthesis and the chlorophyll cold resistant due to freezing temperature is called synthesis is also affected. High light frost stress. Temperature below 10oC, decreases intensity also inhibits photosynthesis. root growth, increases leakage of ions and Change in photoperiod inhibits flowering. ethylene production. ii. Temperature Plants are adapted to a particular region and Some plant parts like they face temperature stress in another region. Seeds, pollen grains and embryos can be a. High temperature stored at very low High temperature causes soil and temperature (–196oC). atmospheric drought. Plants are subjected to permanent wilting in soil drought and temporary wilting in atmospheric drought. iii. Air pollutants Plants generally die above temperature Important atmospheric pollutants of 44oC. However, some organisms like prevalent in the Indian sub-continent are CO , CO, SO , NO , O , fluoride Mastigocladus (a cyanobacterium) grow 2 2 2 3 o o o well at 85 C to 90 C in hot springs. At 42 C and H2S. These pollutants do not cause synthesis of normal protein declines and new visible injury but cause hidden injury. protein called Heat Shock Proteins (HSPs) If the concentration of these pollutants appears. These proteins were discovered increases visible injury like chlorotic in fruit fly Drosophila( melanogaster) and and necrotic spots appear on leaves as since then they have also been discovered well as inhibit photosynthetic carbon in animals, plants and microorganisms. metabolism and biomass formation. Some At high temperature all physiological pollutants at low concentration stimulate processes decline. Photosynthesis decreases plant growth. Example: SO2, NO2 and and respiration increases. So, plants face a NO. Respiration and photorespiration are sensitive to air pollutants. If the shortage of organic substances. concentration of air pollutants is high it inhibits respiration whereas at lower Apple, a temperate concentration stimulates respiration. plant, when planted in Nitrogenous air pollutants under chronic tropical condition fails exposure increases chlorophyll content to produce fruits and while NO2 reduces pigment content at growth is also affected. acute exposure.

200 iv. Edaphic Stress the activity of certain enzymes; Increase in They are divided into two types. They are abscisic acid level ultimately closes down the water stress and salt stress: stomatal apparatus to the minimum, hence, transpiration declines; Protochlorophyll a. Water stress formation is inhibited and photosynthetic A common stress condition arising from process declines; Levels of proline increases; lack of water or excess of water is called Respiration and translocation of assimilates water stress. The abundance of water decreases; Loss of water leads to increase in leads to a stress called flood stress and scarcity of water leads to a stress called the activity of hydrolytic enzymes, followed by destruction of RNA and disruption of protein; drought stress. Wilting in mature leaves is associated with I. Flood Stress carbohydrate depletion due to mobilization The temporary inundation of plants export, followed by leaf senescence. and its parts by flooding causes oxygen Mechanism of drought resistance deficiency to the roots and soil borne Xerophytes are well adapted for drought microorganisms. Effects of flooding are either because, as follows: Nitrogen turnover in the soil i. the protoplasm of such plants does not is reduced; Abscisic acid, ethylene and die when it faces extreme or prolonged ethylene precursors are formed in larger desiccation (dehydration) hence, it amount; Stimulation of partial stomatal tolerates or endures such conditions. closure, epinasty and abscission in Example: Creosote bush (Larrea leaves; Cellular membrane systems break tridentata) can survive water content down, mitochondria and microbodies drops upto 30% whereas, in most disintegrate and enzymes are partially plants the lethal level is below 50–70% inhibited. Flood tolerant plants include or these plants are able to avoid or those found on permanently wet soils. postpone the lethal level of desiccation Examples: Marsh plants, shore plants and because they have developed structural hydrophytes. Tree species found dominant or physiological adaptations. Plants in flooded sites are also tolerant. Examples: that avoid or postpone desiccation have Taxodium disticum, Mangroves and palms evolved an alternative path by developing are tolerant to flood stress. following mechanisms: Improved water uptake by roots which penetrate deep II. Drought Stress down up to the water source; Efficient The term ‘drought’ denotes a period without water conduction by increasing and appreciable precipitation, during which enlarging the conductive tissues in the water content of the soil is reduced to terms of producing more number of such an extent that plants suffer from water xylem elements, dense leaf venation and deficiency. Effects of drought are as follows: reducing the transport distance (short Decrease in cellular growth and synthesis internodes); Restriction of transpiration of cell wall components cause the cells to brought about by stomata present only become smaller in size; Nitrogen fixation on the lower epidermis and covered and its reduction are decreased by decreasing

201 by dense trichomes; Rolling of leaves of toxic sodium carbonate and also help to reduce water uptake by chloride ions. minimizing the transpiring surface; On the basis of salt tolerance, they are Water storage in succulent tissue of Agave grouped into two categories: americana and other CAM plants have 1. Halophytes been found to use water conservatively. 2. Non-halophytes or glycophytes Halophytes are native to saline soils. The Resurrection plants, halophytes which can resist a range of salt those plants having concentration are called as and ability to survive near euryhaline those with narrow range of resistance are total drying which called . Non-halophytes cannot causes them to appear dead. They stenohaline resist salts as the halophytes. recover when water is available. Helianthus tolerates high Mn21 ions. Those which Example: annus Selaginella lepidophylla are present in salt regions face two problems: During drought stress an essential • One is high concentration of salts in protection mechanism that stabilizes the soil water leads to decrease in water cell structure is induced gene expression potential so they grow in opposite direction. Example: of stress protein (dehydrin and osmotin). Salicornia. These proteins protect the • Injuries in salt affected plants caused by in the cytoplasm and in the nucleus, the both osmotic effects and specification cytoskeleton (biomembranes) against effects. Accumulation of chloride denaturation. High desiccation tolerance ions reduces water absorption and transpiration. implies that the protoplasm rehydrates when water becomes available. Plants growing in Salt stress due to deficiency of mineral deserts and arid regions are usually drought elements (K, P, S, Fe, Mo, Zn, Mg, Mn) resistant. causes physiological disorders which lead to reduced growth and yields. b. Salt Stress Presence of high salt concentration in the 1. Salt accumulators absorb and store soil restricts the growth and development salts so that the osmotic potential of their cells continues to remain of plants. Most commonly the plants which negative throughout the growing are present near the seashore and estuaries region. are subjected to salt stress. According to 2. In some salt hardy plants, the excess an estimate about one third of irrigated salt is excluded on the surface of leaves. land on earth is affected by salt stress. Some plants have salt glands which Na1, Cl2, K1, Ca11 and Mg11 ions usually secrete salt (mostly NaCl). The exuded contribute to soil salinity. Plants growing salt absorbs water hygroscopically in such areas face two problems: from the atmosphere. 1. Absorption of water from the soil 3. Some plants lose their excess salt by with negative water potential leaching into the soil or by dropping 2. Interaction with high concentration their salt filled leaves.

202 4. Salt tolerant plants (true halophytes) otherwise known as exponential phase. The synthesize large amounts of the amino three phases are collectively called Grand acid proline, galactosyl glycerol and period of growth. Plant exhibits plasticity in some organic acids which function development. Plant growth and development in osmotic adjustments. are controlled by both internal and external factors. The internal factors are chemical Mechanism of salt tolerance substances called Plant Growth Regulators The plants growing in salty like (PGRs). The hormones are classified halophytes face the problem of excessive into five groups: Auxins, gibberellins, dissolved salts in the solution. Excess of cytokinins, abscisic acid and ethylene. salt creates comparatively more negative These PGRs are synthesized in various parts osmotic potential so that the plants tend to of the plant. PGRs may act synergistically lose water into surrounding medium. Under or antagonistically. The external factors such conditions the plants tend to lose water affecting growth includes water, nutrition, only when their water potential becomes temperature, oxygen and light. Mechanism more negative. It is possible only if they of flowering is controlled by light period absorb excess of salt and accumulate it in (photoperiodism) and temperature their cell saps to maintain the same or higher (vernalization). The physiological changes concentrations as those of outside plants. on flowering with effect from relative length The drawbacks: of light and darkness (photoperiodism) are 1. Salt accumulates in the vacuoles called photoperiodism. A bluish biliprotein 2. The plants become succulents responsible for the perception of light in 3. Accumulated salt dehydrates the photophysiological process (induction cytoplasm and inhibition of flowering) is called 4. Sodium chloride cannot be Phytochrome. Besides photoperiod certain tolerated in the cytoplasm and it plants require a low temperature in the denatures several enzymes earlier stages for flowering. Many biennial Thus, absorption and accumulation of and perennial plants are induced to flower by o o inorganic salts fail to solve the problem. The low temperature (0 C to 5 C). This process is plants however tolerate the salt stress by called vernalization and the reversal effect synthesizing organic compounds that can exist of vernalization is called devernalization. at high salt concentrations without denaturing The condition of a seed when it fails to the enzymes. These organic compounds are germinate even in suitable environmental condition is called . Thus, called nontoxic organic osmotica. Examples: seed dormancy Proline and Betalin (osmoregulators). dormancy can be overcome by following methods such as scarification, impaction, Summary stratification, alternating temperatures and Growth occurs by cell division, cell elongation light. Senescence refers to all collective, and cell maturation. The first phase is lag progressive and deteriorative processes phase, the second is log phase and the final which ultimately lead to complete loss of phase is steady state phase. The log phase is organization and function. Senescence is of four types and they are overall, top, deciduous

203 and progressive. Senescence is controlled by c. ABA d. Auxin plant’s own genetic programme. Death of the 4. Select the correctly matched one plant or its parts consequent to senescence A) Human urine i) Auxin –B is called (PCD). Programmed Cell Death B) Corn gram oil ii) GA3 The final stage of senescence is abscission. C) Fungus iii) Abscisic acid II Abscission is a physiological process of D) Herring fish iv) Kinitin shedding of organs from the parent plant sperm body. The study of functioning of plants E) Unripe maize v) Auxin A under adverse environmental conditions is grains called stress physiology. The environmental F) Young cotton vi) Zeatin stress may broadly be divided into biotic and bolls abiotic stress. The on plants a) A-iii, B-iv, C-v, D-vi, E-i, F-ii, caused by other living organisms such as b) A-v, B-i, C-ii, D-iv, E-vi, F-iii, viruses, bacteria, fungi, parasites, insects, c) A-iii, B-v, C-vi, D-i, E-ii, F-iv, weeds is competing plants are called biotic d) A-ii, B-iii, C-v, D-vi, E-iv, F-i stress. Abiotic stress may occur due to an atmospheric condition or soil condition. 5. Seed dormancy allows the plants to a. overcome unfavourable climatic conditions Evaluation b. develop healthy seeds 1. Select the wrong c. reduce viability statement from the following: d. prevent deterioration of seeds a. Formative phase of 6. Which one of the following method are the cells retain the used to break the seed dormancy? capability of cell division. a) Scarification b) Impaction b. In elongation phase development of c) Stratification d) All the above. central vacuole takes place. 7. What are the parameters used to c. In maturation phase thickening and measure growth of plants? differentiation takes place. 8. What is plasticity? d. In maturation phase, the cells grow 9. Write the physiological effects of further. Cytokinins. 2. If the diameter of the pulley is 6 inches, 10. Describe the mechanism of length of pointer is 10 inches and photoperiodic induction of distance travelled by pointer is flowering. 5 inches. Calculate the actual growth 11. Give a brief account on Programmed in length of plant. Cell Death (PCD) a. 3inches b. 6 inches 12. What are the physiological effects of c. 12 inches d. 30 inches plants facing drought condition? 3. In unisexual plants, sex can be 13. Explain the mechanism of biotic changed by the application of stress. a. Ethanol b. Cytokinins

204 t ICT Corner How do Plants respond to different stimuli?

Let’s Stimulate the Plants.

Steps • Scan the QR code • Click Exploring plant responses • Select items and complete the check list • Follow the procedure – 1 to 10 steps • Record your prediction and not your observation in lab note – Right top

Activity • Observe the movements of plant seedlings and plant parts. • Conclude your observations.

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205 References Unit – 4 Plant Anatomy 1. Fahn.A, (1990), Plant Anatomy, 3rd edition, Oxford; New York; Pergamon Press 2. Gangulee,Das& Data, (2011) College Botany,Vol-II, New Central Bool Agency 3. Katherine Esau, (2006), Anatomy of Seed Plants, 2nd Edition, John Wiley & Sons, Inc. 4. PandeyB.P, (2015), A Textbook of Botany: Angiosperms, New Delhi, S. Chand & Company Ltd. 5. Pijush Roy, (2012), Plant Anatomy, New Central Book Agency (P) Ltd. 6. Ray.F.Evert, (2007), Esau’s Plant Anatomy, 3rd Edition. Wiley-Liss

Unit – 5 Plant Physiology 1. Campbell and Reece (2005) Biology Vol I, 7th Edition, Boston, Pearson,. 2. Clegg C J (2014) Biology, London, Hooder Education,. 3. Data.S.C (1990) Plant Physiology, New Delhi,Willey Eastern. 4. Devlin, R. M. (2017). Outline of Plant Physiology. Medtech Pubs. 5. Dey P.M & Harborne J.B (1997) Plant Bio chemistry, London, Academic press 6. Dey, P. M. and Harborne, J. B. (2013). Plant Bio chemistry. Elsevier. 7. Helgiopik and Stephan Rolfe (2005) The Physiology of Flowering Plants, 4th Edition, London, Cambridge University Press. 8. Jain V.K. (2017) Fundamentals of Plant Physiology, 19th Edition, New Delhi, S.Chand & Co. 9. Jain. J L., Sunjay Jain and Nitin Jain. (2005). Fundamentals of , 6th Edition. New Delhi S. Chand and Co.,. 10. Jane B Reece etal. (2011) Campbell Biology, 10th Edition, Pearson. 11. K.N.Rao, G. Sudhakara Rao, S. Bharatan (1987) The functioning plant, S. Viswanathan Pvt.Ltd. 12. Kumar.A & Purohit S.S (2002) Plant Physiology: Fundamentals and Applications, 2nd Edition, Agro-Bios. 13. Leninger, Nelson and Cox. (2017). Principles of Biochemistry, 7th Edition. NewDelhi, Macmillan Learning. 14. Maria Duca (2015) Plant Physiology, Switzerland, Springer international publishing house. 15. Mukherji, S. and Ghosh, A. K. (2015). Plant Physiology. London, New Central Book Agency Pvt. Ltd., 16. Noggle, G. R. and Fritz, G. J. (1983). Introductory Plant Physiology, Second edition. Prentice Hall India. 17. R.K.Sinha (2004) Modern plant Physiology, Alpha Publishing 18. Salisbury, F. and Ross, C. (1991). Plant Physiology, 4th Edition. India, Thomson Publications. 19. Sinha, R. K. (2003). Modern Plant Physiology, 2nd Ed. Kolkata,Narosa Publishing House. 20. Srivastava H.N (2004) Plant Physiology, Pradeep publication, Jalandhar. 21. Stern, Jansky, Bidlack (2003) Introductory Plant Biology, 9th Edition, New York, McGraw Hill,. 22. SundaraRajan.S (2000) Plant Physiology, New Delhi, Anmol Publication,. 23. Taiz.L and Zeigar.E (2010) Plant Physiology, 3rd Edition, Sunderland, Sinauer Associates, 24. Taiz, L., Zeiger, E., Moller, I. M. and Murphy, A. (2014). Plant Physiology and Development, Sixth Edition. Ingram International Inc. 25. Verma S.K and MohitVerma, (2016) A Text Book of Plant Physiology, Biochemistry and , New Delhi, S.Chand& Co,. 26 Walter Larcher, (2003). Physiological Plant , 4th Edition. New York, Springer International Edition,.

206 Glossary

Abscission zone A region near the base of petiole of leaf which contains abscission layer. Absorption Spectrum A curve obtained by plotting the amount of absorption of different wavelengths of light by a pigment is called its absorption spectrum. Action Spectrum A graphic representation showing the rate of photosynthesis at different wavelengths of light is called action spectrum Aeroponics A technique of growing plants suspended over the nutrient solution in a mist chamber. Nutrient sprayed by motor driven rotor on the roots. Agar Jelly-like substance, derived from red algae Allelopathy The chemical substances released by one plant species which affect or benefit another plant Amphicribal/ Xylem in the centre with phloem surrounding it. Example: Hadrocentric Ferns ( Polypodium) Amphivasal /Leptocentric Phloem in the centre with xylem surrounding it. Example: Dragon plant – Dracena and Yucca Anabolic It is an enzyme catalyzed reaction in a cell that involves synthesis of complex molecules from simple molecules which uses energy. Apical cell theory Single apical cell growing into whole plant Axil Parenchyma Parenchyma arranged longitudinally along the axis Callose Sieve pores are blocked by substances called callose Carbonic acid A weak acidic solution of carbon-di-oxide dissolved in water Catabolic It is an enzyme catalyzed reaction in a cell that involves degradation of molecules into simple subunits which release energy. Chelating agents A chelate is the soluble product formed when certain atoms in an organic ligand donate electrons to the cation. Chlorosis Breakdown of chlorophylls leads to yellowing of leaves Closed vascular bundle Cambium absent between xylem and phloem Example: Monocot stem Coenzyme A non-protein molecule involved in enzyme catalyzed reactions serves as transfer of protons or electrons between various molecules Colloidal An evenly distributed mixture of two different particles in a system without losing its own properties. Deamination The enzymatic removal of an amino group from an amino acid to form its corresponding keto acid. Desiccation tolerance Ability of plants which can tolerate extreme water stress without being killed. Drought resistance Capacity of a plant to limit and control consequences of water deficit.

207 EDTA Ethylene Diamine Tetra Acetic acid, chelating agent makes iron uptake possible by forming soluble complex in an alkaline soil. Endergonic A chemical reaction with a positive free energy charge or ATP utilizing reactions. Exergonic A chemical reaction with a negative free energy charge or ATP producing reactions. Extra stellar ground tissue Tissues outside the stele Fibre-Tracheids Transitional form between fibre and tracheids Fluorescence Emission of light by a substance that has absorbed light in the form luminescence. Gelatin An animal-based product used as a gelling agent. Granum A stack of thylakoid in a stroma of chloroplast Hadrome Xylem-by Haberlandt Halophytes Plants native to saline soils and complete their life cycle Heliophytes Plants which are adapted to light Differentiate tissues from undifferentiated cells of meristem Indeterminate growth Plants grow throughout their life Intrastelar ground tissue Tissues within the stele Isomerisation Rearrangement of atomic groups within the same molecule without any loss or gain of atoms. Leptome Phloem – by Haberlandt Lumen Space inside the tracheid/vessel/fibres Malate Shuttle mechanism It is a biochemical system for translocating electrons produced from glycolysis across inner membrane of mitochondrion for oxidative phosphorylation. Mass meristem Meristem which divides in all planes Necrosis Death of tissue Non heme iron An iron porphyrin prosthetic group of heme proteins from plant origin Nutation The growing stems of twiner and tendrils show automatic movement Open vascular bundle Cambium present between xylem and phloem Example: Dicot stem Oxidation Water is oxidised into Oxygen (loss of electrons) PAR The wavelength at which the rate of photosynthesis is more is called ‘Photosynthetically Active Radiations’ which falls between 400 to 700 nm. Phosphorescence Phosphorescence is the delayed emission of absorbed radiations. Photolysis Splitting of water molecules by light which generate protons, electrons and oxygen. Photon Light is electromagnetic radiant energy and travels as tiny particles called photons. A discrete Physical unit of light energy.

208 Photoperiodism The response of plants to the photoperiod expressed in the form of flowering. Phytochrome A photo reversible proteinaceous plant pigment in very low concentration that absorbs red and far red light which controls flowering. Pitted thickening Uniformly thick except at their pits Preparatory phase First half of glycolysis comprising five enzymatic reactions in which one molecule of glucose splitting into two molecules of glyceraldehyde 3 phosphate with consumption of two ATP molecules. Prickles Stiff and sharp outgrowth Quantasome Morphological expression of physiological photosynthetic units, located on the inner membrane of thylakoid lamellae. Act as photosynthetic unit contains 200 to 300 chlorophyll molecules. Quantum The energy contained in a photon is represented as quantum Quantum requirement The number of photons or quanta required to release one molecule of oxygen during photosynthesis Quantum yield The number of oxygen molecules produced per quantum of light absorbed. Quiescent centre concept Inactive region of root meristem Radial vascular bundles Xylem and phloem present on different radii Ray Parenchyma Parenchyma cells arranged in radial rows Redox reactions Oxidation (loss of electrons) and Reduction (gain of electrons) reactions are called redox reactions. Reduction CO2 is reduced into Carbohydrates (gain of electrons) Rib-meristem Meristem which divides anticlinally in two planes RUBISCO Enzyme responsible for fixation of Carbon dioxide, the most abundant protein (Ribulose 1,5 bisphosphate Carboxylase Oxygenase) Salt stress Adverse effects of excess mineral salts on plants Sap It is a fluid consist of water and dissolved minerals Slime body A special protein (Phloem Protein) in sieve tubes Stellate hairs Star shaped hairs Stratification A process of breaking the dormancy of some plants resulting from chilling requirements Subsidiary cells Surrounding guard cells in the leaf epidermis Sucrose Non-reducing disaccharide composed of glucose and fructose Trichoblasts One type of epidermal cells that is also called short cell Trichomes Unicellular or multicellular appendages Tunica-carpus theory Two zones of apical meristem Tunica and Carpus Xylos Wood

209 Competitive Exam Questions

Unit -4 – Plant Anatomy 6. The annular and spirally thickened conducting elements generally develop in 1. The balloon – shaped structures called the protoxylem when the root or stem is tyloses (NEET II – 2016 ) (CBSE -AIPMT 2009)  Ă͘ ŽƌŝŐŝŶĂte in the lumen of vessels a. maturing b. elongating b. characterise the sap wood c. widening d. differentiating c. are extensions of xylem parenchyma cells into vessels 7. Anatomically fairly old dicotyledonous root d. are linked to the ascent of sap through is distinguished from the dicotyledonous xylem vessels stem by the (CBSE- AIPMT 2009) a. absence of secondary xylem 2. Cortex is the region found between (NEET b. absence of secondary phloem II – 2016) c. presence of cortex a. epidermis and stele d. position of protoxylem b. pericycle and endodermis c. endodermis and pith 8. In barley stem, vascular bundles are (CBSE d. endodermis and vascular bundle -AIPMT 2009) a. open and scattered 3. Read I – IV and find the correct order of b. closed and scattered components from outer side to inner side c. open and in a ring in a woody dicot stem (CBSE -AIPMT – d. closed and radial 2015) (I) secondary Cortex (II) wood 9. Palisade parenchyma is absent in the leaves (III) secondary phloem (IV) phellem of (CBSE- AIPMT 2009) a. III, IV, II and I b. I, II, IV and III a. sorghum b. mustard c. IV, I, III and II d. IV, III, I and II c. soyabean d. gram 4. You are given a fairly old piece of a dicot 10. Sugarcane plant has (AIIMS 2009) stem and a dicot root. Which of the a. reticulate venation following anatomical structures will you b. capsular fruits use to distinguish between the two? (CBSE c. pentamerous flowers -AIPMT 2014) d. dump-bell shaped guard cells a. secondary xylem 11. Vascular tissues in flowering plants develop b. secondary phloem from (CBSE- AIPMT 2008 & JIPMER c. protoxylem 2012) d. cortical cells a. phellogen 5. Heart wood differs from sapwood in (CBSE b. plerome c. periblem d. dermatogen -AIPMT 2010) a. the presence of rays and fibres 12. The length of different internodes in a culm b. the absence of vessels and parenchyma of sugarcane is variable because of (CBSE c. having dead and non-conducting -AIPMT 2008) elements a. short apical meristem d. being susceptible to hosts and pathogens b. position of axillary buds

214 c. size of leaf lamina at the node below each characterized by (CBSE -AIPMT 2003) internode a. having dense cytoplasm and d. intercalary meristems prominent nucleus b. having light cytoplasm and small 13. Passage cells are thin-walled cells found in nucleus (CBSE -AIPMT 2007) c. dividing regularly to add to the corpus a. endodermis of roots facilitating rapid d. dividing regularly to add to tunica transport of water from cortex to pericycle 18. P. Protein is found in (CBSE- AIPMT 2000) b. phloem elements that serve as entry a. parenchyma b. collenchyma points for substances for transport to c. sieve tube d. xylem other plant parts c. testa of seeds to enable emergence of 19. Specialized epidermal cells surrounding the growing embryonic axis during seed guard cells are called (NEET (I) 2016) germination a. bulliform cells d. central region of style through which b. lenticels the grows towards the c. complementary cells d. subsidiary cells 14. Which one of the following is not a lateral meristem (CBSE -AIPMT 2010) Directions: a. interfascicular cambium The following questions 20 & 21 consist of two b. phellogen statements, one labelled Assertion and the another labelled . Select the correct c. intercalary meristem Reason d. intrafascicular cambium answer from the codes given below: a) Both assertion and reason are true and 15. A common feature of vessel elements and reason is the correct explanation of assertion sieve tube elements is (CBSE- AIPMT 2007) b) Both assertion and reason are true, but a. enucleate condition reason is not the correct explanation of b. presence of P. Protein assertion c. thick secondary wall c) Assertion is true but reason is false d. pores on lateral walls d) Assertion and reason are false

16. In a longitudinal section of a root, starting 20. Assertion: Conducting tissues, especially from the tip upward, the four zones occur xylem show greatest reduction in submerged in the following order (CBSE -AIPMT hydrophytes. 2004) Hydrophytes live in water. So no a. root cap, cell division, cell enlargement, Reason: need of tissues. (AIIMS – 2010) cell maturation b. root cap, cell division, cell maturation, Ans: c. cell enlargement 21. Assertion: Long distance flow of photo c. cell division, cell enlargement, cell assimilates in plants occurs through sieve maturation, root cap tubes. d. cell division, cell maturation, cell Reason: Mature sieve tubes have partial enlargement, root cap cytoplasm and perforated sieve plates (AIIMS – 2012) 17. The cells of the quiescent centre are Ans: a.

215 22. Duramen is present in (JIPMER 2016) a. phelloderm b.primary phloem a. the inner region of secondary wood c. secondary xylem d. periderm b. a part of sap wood c. the outer region of secondary wood 30. Which of the following plants shows multiple d. region of pericycle epidermis? (Manipal 2012) a. Croton b. Allium 23. The interxylary phloem is found in the stem c. Nerium d. Cucurbita of (JIPMER 2013) a. Cucurbita b. Salvia UNIT -5 PLANT PHYSIOLOGY c. Calotropis d. none of these 1. The water potential of pure water is (NEET 24. is due to (JIPMER 2013) 2017) a. ventral meristem a. Less than zero b. secondary meristem b. More than zero but less than one c. primary meristem c. More than one d. all of these d. Zero 25. Which of the following tissues consists of 2. Transpiration and root pressure cause living cells (JIPMER 2012) water to rise in plants by (NEET 2015) a. vessels b. tracheids a. pulling it upward d. sclerenchyma c. companion cell b. pulling and pushing it, respectively 26. The Quiescent centre in root meristem c. pushing it upward serves as a (JIPMER 2011) d. pushing and pulling it, respectively a. site for storage of food, which is utilized 3. Movement of ions or molecules in a during maturation direction opposite to that of prevailing b. reservoir of growth hormones electro-chemical gradient is known as c. reserve for replenishment of damaged (C.B.S.E. 2000) cells of the meristem a. Active transport d. region for absorption of water b. Pinocytosis 27. In the sieve elements, which one of the c. Brownian movement following is the most likely function of d. Diffusion P.Proteins? (JIPMER 2011) a) Deposition of callose on sieve plates 4. Correct sequence of events in wilting? b. Providing energy for active translocation (P.M.T. Kerala 2001) c. Autolytic enzymes a. Exosmosis-deplasmolysis-temporary and permanent wilting d. Sealing-off mechanism on wounding b. Exosmosis-plasmolysis-temporary 28 .Which of the following is made up of dead and permanent wilting cells? (NEET 2017) c. Endosmosis-plasmolysis-temporary a. Xylem parenchyma b. Collenchyma and permanent wilting c. Phellem d. Phloem d. Endosmosis-deplasmolysis - temporary 29. The vascular cambium normally gives rise to and permanent wilting (NEET 2017) e. Exosmosis-deplasmolysis-plasmolysis - temporary and permanent wilting

216 5. What will be the direction of net osmotic b. Water plus minerals movement of water if a solution 'A', c. Water plus enzymes enclosed in a semi permeable membrane, d. All of these having an osmotic potential of'- 30' bars and turgor pressure of '5' bars is submerged 12. Stomata of a plant open due to (CBSE 2003) in a solution 'B' with an osmotic potential of a. Influx of potassium ions '- 10' bars and '0' turgor pressure ? (C.E.T. b. Efflux of potassium ions Karnataka 2002) c. Influx of hydrogen ions a. Equal movement in both directions d. Influx of calcium ions b. 'B' to 'A' 13. Potometer works on the principle of c. No movement (CBSE 2000) d. 'A' to 'B' a. Osmotic pressure 6. The pressure exerted by a swollen vacuole b. Amount of water absorbed equals the on the cell wall is (C.M.C. Vellore 2002) amount transpired a. OP b. WP c. Potential difference between the tip of c. TP d. DPD the tube and then of the plant d. Root pressure 7. Who said that ‘transpiration is a necessary evil’? (JIPMER-2006) 14. Most suitable theory for ascent of sap is a. Curtis b. Steward (CBSE 1991, CPMT-UP 1995) c. Anderson d. J.C.Bose a. Transpirational pull and cohesion theory of Dixon and Jolly 8. Which one gives the most valid and recent b. Pulsation theory of J.C. Bose explanation for stomatal movements? c. Relay pump theory of Godlewski (NEET 2015) d. None of these a. Transpiration 15. If a cell kept in a solution of unknown b. Potassium influx and efflux concentration gets deplasmolysed, the c. Starch hydrolysis solution is, (CPMT-UP 1996) d. Guard cell photosynthesis a. Detonic b. Hypertonic 9. Carrier proteins are involved in ( P M T - c. Isotonic d. Hypotonic UP-1998) 16. Which is essential for the growth of root tip a. Active transport of ions ? (NEET PHASE II 2016) b. Passive transport of ions a. Zn b. Fe c. Water transport c. Ca d. Mn d. Water evaporation 17. On the basis of symptoms of chlorosis in leaves, a student inferred that this was due to 10. Active transport of ions in the cell requires deficiency of nitrogen. The inference could (PMT MP 2002) be correct only if we assume that yellowing a. High temperature b. ATP of leaves appeared first in (AIIMS 2007) c. Alkaline pH d. Salts a. old leaves b. young leaves 11. Guttated liquid is (AFMC 2002) c. young leaves followed by mature leaves a. Pure water d. mature leaves followed by young leaves.

217 18. Cytochrome oxidase contains (UP CPMT atmospheric nitrogen in leguminous plants 2006) is _____ (AIPMT 2013) a. Iron b. Magnesium a. NO-3 b. glutamate c. Zinc d. Copper c. NO-2 d. ammonia

19. Which is correct to saprophytic 26. C4 plants are more efficient in photosynthesis angiosperms? (UP CPMT 2006) than C3 plants due to (AIPMT 2010) a. They secrete enzyme outside the body a. presence of thin cuticle and absorb b. lower rate of photorespiration b. They have mycorrhizae fungi c. higher leaf area c. They take food and then digest it d. presence of larger number of chloroplast d. They are photosynthetic in the leaf cells.

20. The ability of the venus fly trap to capture 27. Chlorophyll b is (JIPMER 1980)

insects is due to (JIPMER 2008) a. C54H70 O6 N4 Mg a. chemical stimulation by the prey b. C55H70 O6 N4 Mg b. a passive process requiring no special c. C55H72 O5 N4 Mg ability on the part of the plant. d. C45H72 O5 N4 Mg c. Specialized muscle like cells 28. Synthesis of ADP + Pi ATP in grana is d. rapid turgor pressure changes o (AIIMS 1993) 21. Boron in green plants assists in (RPMT a. phosphorylation 2007) b. photophosphorylation a. photosynthesis c. oxidative phosphorylation b. Sugar transport d. photolysis c. activation of enzyme d. acting as enzyme cofactor 29. In chloroplast, chlorophyll is present in the (AIPMT 2004) 22. Which of the following elements is very a. stroma essential for the uptake of Ca2+ and b. outer membrane membrane function? (Kerala CEE 2007) c. inner membrane a. phosphorus b. molybdenum d. thylakoids c. manganese d. boron 30. Electrons from the excited chlorophyll 23. Sulphur is not a constituent of (AMU 2011) molecule of photosystem II are accepted a. cysteine b. methionine first by (AIPMT 2008) c. ferredoxin d. pyridoxine a. quinone b. ferredoxin c. cytochrome-b d. cytochrome-f 24. Deficiency symptoms of nitrogen and potassium are visible first in _____ (AIPMT 31. Read the following four statements A,B,C 2014) and D. Select the right option (AIPMT 2010) a. senescent leaves b. young leaves A. Z scheme of light reaction takes place in c. roots d. buds the presence of PS I only B. only PS I is functional in cyclic 25. The first stable product of fixation of photophosphorylation

218 C. cyclic photophosphorylation results into improved efficiency of nitrogen utilization. synthesis of ATP and NADPH2 In which of the following physiological D. stroma lamellae lack PS II as well as groups would you assign this plant? (NEET NADP PHASE I 2016) b. CAM a. A and B b. B and C a. C4 c. Nitrogen fixer d. C c. C and D d. B and D 3

32. Photolysis of each water molecule in light 37. Emerson's enhancement effect and Red reaction will yield ___ (Kerala CEE 2007) drop have been instrumental in the a. 2 electrons and 4 protons discovery of (NEET PHASE I 2016) b. 4 electrons and 4 protons a. two photosystems operating c. 4 electrons and 3 protons simultaneously b. photophosphorylation and cyclic d. 2 electrons and 2 protons electron transport 33. Photosynthetic active radiation (PAR) has c. oxidative phosphorylation the following range of wavelength (AIPMT d. photophosphorylation and non-cyclic 2005) electron transport a. 400-700 nm b. 450-920 nm c. 340-450 nm d. 500-600 nm 38. The process which makes major difference between C3 and C4 plants is (NEET PHASE 34. Phosphoenol pyruvate (PEP) is the primary II 2016)

CO2 acceptor in __ (NEET 2017) a. glycolysis b. calvin cycle a. C plants 3 b. C4 plants c. photorespiration d. respiration

c. C2 plants d. C3 and C4 plants 39. In a chloroplast the highest number of 35. With reference to factors affecting the rate protons are found in (NEET PHASE I 2016) of photosynthesis, which of the following a. lumen of thylakoids statements is not correct? (NEET 2017) b. inter membrane space

a light saturation for CO2 fixation occurs at c. antennae complex 10 % of full sunlight d. stroma

b. increasing atmospheric CO2 concentration up to 0.05% can enhance 40. Oxidative phosphorylation is (NEET 2016) CO2 fixation rate a. formation of ATP by transfer of phosphate c. C3 plants respond to higher temperature group from a substrate to ADP with enhanced photosynthesis while C4 plants have much lower temperature b. oxidation of phosphate group in ATP optimum. c. Aaddition of phosphate group to ATP d. tomato is a greenhouse crop which can d. formation of ATP by energy released

be grown in CO2 enriched atmosphere from electrons during substrate for higher yield oxidation.

36. A plant in your garden avoids 41. Which of the biomolecules is common to photorespiratory losses, has improved respiration-mediated breakdown of fats, water use efficiency, shows high rates of carbohydrates and proteins? (NEET photosynthesis at high temperatures and has 2013, 2016)

219 a. glucose-6-phosphate a. malic acid and acetyl coenzyme b. fructose1,6-bisphosphate b. oxaloacetic acid and acetyl coenzyme c. pyruvic acid c. succinic acid and pyruvic acid d. acetyl CoA d. fumaric acid and pyruvic acid

42 Which statement is wrong for Krebs cycle? 46. Respiration is a process in which (CPMT (NEET 2017) 1980) a. there is one point in the cycle where FAD a. energy is used up

is reduced to FADH2 b. energy is stored in the form of ADP b. during conversion of succinyl CoA c. energy is released and stored in the to succinic acid, a molecule of GTP is form of ATP synthesised. d. energy is not released at all c. the cycle starts with condensation of acetyl group a.cetyl CoA. with pyruvic 47. The common phase between aerobic and acid to yield citric acid anaerobic respiration is called (CPMT d. there are three points in the cycle where 1984) NAD+ is reduced to NADH+H+ a. glycolysis b. krebs cycle 43. The three boxes in this diagram represents c. tricarboxylic acid cycle the three major biosynthetic pathways in d. oxidative phosphorylation aerobic respiration and arrows represent net reacts or products. (NEET 2013) 48. ATP synthesis occurs on/in the ( A IIMS 1984) a. matrix b. outer membrane of mitochondrion Arrows numbered 4, 8 and 12 can be c. innermembrane of mitochondrion a. ATP d. none of the above b. H O 2 49. Which 5-carbon organic acid of the c. FAD or FADH 2 Krebs cycle is a key compound in the N2 d. NADH metabolism of a cell (AIIMS 1989) a. citric acid 44. The energy released metabolic process in which substrate is oxidised without an b. fumaric acid external electron acceptor is called c. oxalosuccinic acid (AIPMT 2010) d. α-Ketoglutaric acid a. glycolysis 50. Which one of the following acts as a b. fermentation hormone involved in ripening of fruits c. aerobic respiration (CBSE PMT 2000) d. photorespiration a. naphthalene acetic acid 45. Krebs cycle starts with the formation of six b. ethylene carbon compound by a reaction between c. indole acetic acid (CPMT 1980) d. zeatin

220 51. Coconut milk factor is (PMT 2003) 59. Root development is promoted by a. auxin b. gibberellin (AIPMT 2010) c. abscisic acid d. cytokinin a. Auxin b. Gibberellin c. Ethylene d. Abscisic acid 52. Banana is seedless because (JIPMER 2004) 60. Senscence as an active developmental cellular a. it produces asexually process in the growth and functioning of b. auxin is sprayed a is indicated in (AIPMT c. both A and B 2008) d. none of the above a. Annual plants b. Floral plants 53. Pruning of plants promotes branching due c. Vessels and Tracheid differentiation to sensation of axillary buds by (AIIMS d. Leaf abscission 2004) a. Ethylene b. Gibberellin 61. You are given a tissue with its potential c. IAA d. Cytokinin for differentiation in an artificial culture. Which of the following pairs of hormones 54 Avena curvature test is bioassay for activity would you add to the medium to secure of (AIIMS 2006) (NEET 2016) shoots as well as roots? a. Auxin b. Ethylene (NEET 2016) c.Cytokinin d. Gibberellin a. Gibberellin and abscissic acid b. IAA and gibberellins 55. One of the synthetic auxin is (AIPMT 2009) c. Auxin and cytokinin d. Auxin and abscisic acid a. IBA b. NAA c. IAA d. GA 62. Phytochrome is a (NEET 2016)

56 Which one of the following acids is a. Chromo protein derivative of carotenoids (AIPMT 2009) b. Flavo protein c. Glyco protein a. Abscisic acid b. Indole butyric acid d. Lipo protein c. Indole – 3 acetic 63. Typical growth curve in plants is d. Gibberellic acid (NEET 2016) a. Linear 57. Photoperiodism was first characterized in (AIPMT 2010) b. Stair – steps shaped c. Parabolic a. Cotton b. Tobacco c. Potato d. Tomato d. Sigmoid

58. One of the commonly used plant growth hormone in tea plantations is (AIPMT 2010) a. Abscisic acid b. Zeatin c. Indole – 3 – acetic acid d. Ethylene

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223 NOTES

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