Plant Kingdom

1. What is the basis for the classification of algae?

Solution:

Initially, algae classification was based on a single visible character in the form of the colour of the thallus. Accordingly, three main algal divisions were recognised – Green algae, Brown algae and Red algae. However, at present, in addition to the colour, some more characteristics are taken into consideration for algal division. Some of them are:

a. Type of photosynthetic pigments present b. Nature of the stored food c. Composition of the cell wall d. Number and position of the flagella e. Pattern of life cycle

Based on the above features, algae have been classified into three main classes – Chlorophyceae (green alga), Phaeophyceae (brown alga) and Rhodophyceae (red alga).

2. When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?

Solution:

Reduction division is a meiotic cell division, and it occurs in the reproductive organs at different stages of the life cycle. The usual sequence of steps leading to reductional division across all species of plants is as follows: a. The spore mother cell is formed by the sporophytic generation and is a diploid cell. b. The spore mother cell (2n) undergoes reductional division to form haploid spores (n). c. A haploid spore germinates and marks the beginning of the gametophytic generation.

In liverworts and moss, for instance, the sporophyte that depends on the gametophyte, bears the spore mother cell. It undergoes meiotic division to form haploid spores inside the capsule, which germinate and form free living gametophyte. In ferns, the spore mother cell is formed inside the sporangia of the dominant sporophyte. It undergoes meiotic division to form haploid spores. The spores, after liberation, germinate to form prothallus and mark the beginning of the gametophytic generation.

In gymnosperms, the spore mother cell is present in the microsporangia / megasporangia borne on the microsporophyll / megasporophyll. It undergoes meiotic division to form haploid male and female gametes, in the form of egg and pollen. In angiosperms, the (dominant phase) main plant is a sporophyte and bears flowers with anther and pistil, which is the site of occurrence of the spore mother cell. The spore mother cell undergoes meiotic division to form pollen/egg cell.

3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Solution:

Archegonium is a female sex organ having the egg cell enclosed by a protective layer. It is present in bryophytes, pteridophytes, and gymnosperms. Life cycle of bryophytes

1. The plant body is thallus-like in lower bryophytes, while in higher forms it can be differentiated into rhizoids, stem and leaves. Functionally, they are equivalent to roots.

2. The dominant phase is a free-living thalloid gametophyte (haploid) , which lacks vascular tissues. Reproduction is brought about by vegetative and sexual means. 3. Sexual reproduction is highly oogamous and takes place with the aid of the male and female organs of reproduction, called the antheridia and the archegonia . The former is club-shaped, and the latter flask-shaped. The sex organs are jacketed and multi-cellular. The archegonium is flask-shaped with a five or six rowed tubular neck and a broader single to multi-walled venter. The venter contains a non-motile oosphere. Each antheridum produces biciliate antherozoids. 4. Fertilisation occurs in the presence of moisture. The male gamete swims to the female sex organ and movement is chemotactic (sucrose). The fusion of the male and female gametes results in a zygote. Since water is required for the completion of the life cycle, bryophytes are known as the amphibians of the plant kingdom. 5. Sporophytic generation is never independent, but is parasitic over the gametophyte. Sporophyte can be differentiated into foot, seta and capsule. 6. The capsule consists of a diploid spore mother cell. It undergoes reductional division to form haploid spores. All spores are similar, and after liberation, they germinate to form thalloid protonema . Protonema finally gives rise to a new haploid pplant. 7. There are two well-defined generations in the life cycle of all bryophytes. 8. The life cycle of all bryophytes has heteromorphic alteration of haploid gametophytes and diploid sporophyte. It is known as haplodiplontic life cycle. 9. The stages before fertilisation and after reduction division contain haploid set of chromosomes, while the stages after fertilisation and after reductional division contain a diploid set of chromosomes. The former is called gametophytic generation and the latter is known as sporophytic generation . This phenomenon is known as alternation of generation , which is a characteristic feature of this group.

10.

4. Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of moncot, ovum of a liverwort, and zygote of a fern.

Solution:

Protonemal cell of moss: Haploid (n) Primary endosperm nucleus in dicot: Triploid (3n) Leaf cell of a moss: Haploid (n) Prothallus cell of a fern: Haploid (n) Gemma cell in Marchantia: Haploid (n) Meristem cell of moncot: Diploid (2n) Ovum of a liverwort: Haploid (n) Zygote of a fern: Diploid (2n)

5. Write a note on the economic importance of algae and gymnosperm.

Solution: The economic importance of algae is: 1. Producer of aquatic systems: Algae are major producers of all aquatic ecosystems.

2. CO 2-O2 balance: About 50% of the total global CO 2 is fixed by algae through the process of photosynthesis. They increase the level of dissolved oxygen in water, thereby making life congenial for aquatic organisms. 3. Food: a. About 70 species of marine algae are used as food. b. Some are utilised as fodder, for example Porphyra, Laminaria, Sargassum, etc. 4. Hydrocolloids: Red and brown algae are good sources of colloids like carrageen, algin, agar-agar, funori, etc. 5. Single cell protein (SLP) - Spirulina and chlorella are rich sources of proteins, vitamin and minerals. - They are widely used as food supplements. 6. Minerals: - Bromine, iodine, etc. are extracted from algae.

7. Medicines: - Codium, Chlorella, Laminnaria, Durvillaea, etc, have medicinal importance.

Economic importance of gymnosperms: 1. Ornamental uses: Cycas revolute, Thuja, Criptomeria etc. are usually cultivated in gardens as ornamental plants.

2. Source of wood: - Many gymnosperm trees, particularly conifers (example pine, cedar, etc) are of great importance for their light-coloured, straight, light- weight soft wood. - The wood is extensively used as timber for building material, in making furniture and closets, match boxes, pencils, railway sleepers, paper pulp and as fuel.

3.Edible Products: a. The stem and seeds of the cycas yield “sago” starch. b. The seeds of many cycads and conifers are edible. c. The seeds of “Pinus gerardiana” are used as dry fruits, called “Chilgoza”.

4. Medicinal uses: a. Species of Ephedra yield an alkaloid called “ephedrine.” b. “Ephedrine” is used in the preparation of medicines for the treatment of cough, asthma and bronchitis.

5. Resins: a. Resins are semi-fluid substances secreted in the ducts, cavities or canals of coniferous trees. b. The resins are complex oxidation products of various essential oils containing terpenes, resin acids and esters. c. The resins are chiefly used in the manufactures of varnishes, water- proof paints, sealing wax, etc. d. Some common resins obtained from various sources are: (a) Copal obtained from Agathis australis. (b) Resins obtained from pine. (c) Canada balsam obtained from Abies balsamea.

6. Tannins: Tannins are complex phenolic substances obtained from the bark of Tsugo condenses.

7. Essential oils: Many gymnosperms yield essential oils that are used in perfumery and as flavouring agents.

6. Both gymnosperms and angiosperms bear seeds, but then, why are they classified separately?

Solution: Gymnosperms and angiosperms are classified separately because of the following reasons: 1. The sex organs in gymnosperms are in the form of cones, whereas in angiosperms, they are present in the form of flowers.

2. The ovules of gymnosperms are naked, but in angiosperms, they are enclosed inside the ovary.

3. The endosperm in gymnosperms is haploid and it is formed before fertilisation. In angiosperms, the endosperm is fertilised product and it is triploid.

4. Gymnosperms lack fruits, and the seeds are naked, whereas fruits that enclose seeds are present in angiosperms.

5. In gymnosperms, the wood is non-porous, and lacks vessels. In angiosperms, the wood is porous, and vessels are present.

6. Archegonium is present in gymnosperms. In angiosperms, it is absent and gets modified into egg apparatus.

7. What is heterospory? Briefly comment on its significance. Give two examples.

Solution: Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as the microspore and the larger one is known as the megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. Significance of heterospory: A heterosporous condition leads to the precocious development of gametophytes that has ultimately led to the seed habit. The evolutionary trend is marked by the development of two different kinds of spores, and the retention of the larger spore within the plant body. This ensures a proper development of the sporophyte, and eventually leads to the development of an independent and dominant sporophytic generation. As we proceed along the evolutionary ladder, there is progressive loss of the independent existence of gametophytes, and they have become increasingly dependent upon the parent sporophyte for nourishment. The trend started in pteriophytes in the form of heterosporous condition that eventually led to the seed habit. Finally, it evolved fully in angiosperms where the dominant part of the life cycle is sporophyte. Heterospory, therefore, is considered an important step in evolution, since it is a precursor to the seed habit. Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.

8. Explain briefly the following terms with suitable examples:-

(i) protonema (ii) antheridium (iii) archegonium (iv) diplonic (v) sporophyll (vi) isogamy

Solution: (i) Protonema: It is the juvenile, filamentous, autotrophic and gametophytic stage in the life of the moss. Sometimes, the protonemal branch is differentiated into primary protonemal and secondary protonemal branches. (ii) Antheridium: Antheridium is the male sex organ that produces male gametes, spermatozoids or antherozoids, in bryophytes and pteridophytes. It is borne on the gametophyte. It is multi-cellular and is enclosed in a sterile layer of jacket cells. (iii) Archegonium: a. The female sex organ of bryophytes and pteridophytes is called the “archegonium” and is present on the gametophyte. b. It is multi-cellular and is enclosed in a sterile layer of jacket cells. c. Each archegonium is differentiated into a tubular neck and a swollen venter. d. The venter possesses the female gamete or egg and becomes oospore after fertilisation.

(iv) Diplontic: a. It is a kind of life cycle in plants where diploid sporophyte is the dominant phase. b. The sporophyte is independent and photosynthetic. c. The gametophytic phase is represented by the single to a few celled haploid gametophyte that bears gamets. d. Diplontic life cycle is exhibited by gymnosperms and angiosperms. e. Some alga like focus exhibits diplontic life cycle. f. The life cycle is marked by reductional division occurring before fertilisation. For example, focus, cladophora, etc.

(v) Sporophyll: a. The leaf-bearing sporangia is called sporophyll. For example, fern leaf, stamen, carpel, microsporophyll of cycas, pinus, megasporophyll of pinus and cycas. (vi) Isogamy: a. it is a kind of sexual fusion I which the two fusing gametes are morphologically and physiologically similar. For example chlamydomonas, Ectocarpus, etc.

9. Differentiate between the following:

(i) Red algae and brown algae (ii) Liverworts and moss (i) Homosporous and heterosporous pteridophyte (i) Syngamy and triple fusion

Solution:

(i) Red algae and Brown algae

Red algae Brown algae Reddish in colour Browinsh in colour Photosynthetic pigment in the Photosynthetic pigment in the form of chlorophyll a, d and form of chlorophyll a, c and phycoerythrin. fucoxanthin. Food is stored in the form of Food is stored in the form of floridean starch mannitol and laminarin. Cell walls are composed of Cell walls are composed of cellulose, pectin and cellulose and algin. phycocolloids. No motile stage in life cycle. Motile stage characterised by the presence of flagella. Very elaborate and complex Post-fertilisation stages are post-fertilisation stages. simple.

(ii) Liverworts and Moss

Liverworts Moss They have dorsiventral flat They have radial symmetry. morphology. Plants are generally thalloid, They are foliage, with lateral with dichotomous branching. branching. Leaves are devoid of a midrib. Leaves possess an unbranched midrib. Rhizoids are unicellular and Rhizoids are branched and unbranched. multi-cellular with oblique septa. Sex organs develop in Sex organs develop apically. intercalary position. Sporophyte is simple with or Sporophyte is always without foot, seta and capsule. differentiated into foot, seta and The capsule is devoid of capsule. The capsules have collumella. collumella. Sporophyte is completely Sporophyte is partially dependent upon gametophyte dependent upon gametophyte as as it lacks any photosynthetic it bears photosynthetic tissue. tissue. Protonema stage is absent. Protonema stage is present. E.g. E.g. Marchantia Funaria

(iii) Homosporous and Heterosporous pteridophyte

Homosporous pteridophyta Heterosporous pteridophytes All spores are similar in size and Spores are of two types – the type. smaller microscope and the larger megaspore. The sporangia and sporophylls do The sporangia and sporophylls are not show any differentiation and differentiated into two types – specialisation. microsporangia on microsporophyll and megasporangia on megasporophyll They usually bear both types of sex There are two types of prothalli – organs male-bearing antheridia and female- bearing archegonia. There is no precocious development Precocious development of of gametophyte. gametophyte is seen, which ultimately led to the seed habit.

(iv) Syngamy and Triple fusion

Syngamy Triple fusion It represents generative fertilisation. It represents vegetative fertilisation. One male gamete fuses with a non- One male gamete fuses with a motile female gamete to produce a secondary nucleus or two polar

zygote. nuclei to form a primary endosperm nucleus (3n). It forms a diploid cell. It forms a triploid cell. The product of syngamy grooms to The product of triple fusion gives form the embryo or future plant. rise to endosperm.

10. How would you distinguish monocots from dicots?

Solution: Dicot Monocot The seeds of the plant have two The seeds of the plant have one cotyledons. cotyledons. Leaves show reticulate venation. Leaves show parallel venation. Stomata are generally kidney- Stomata are commonly shaped dumbbell-shaped. They generally possess tap root They possess adventitious system. roots. Flowers are tetramerous or Flowers are trimerous. pentamerous. In stem, the vascular bundles are The vascular bundles are arranged in a single ring. scattered in the ground tissue of stem. In stem, each vascular bundle is covered by a sheath of sclerenchyma. Vascular bundles of the stem are Vascular bundles of the stem conjoint, collateral and open. are conjoint, collateral and closed. Stem shows secondary growth. Secondary growth is absent. Root is generally devoid of pith. A pith is present at the centre of root.

11 . Match the followings (column I with column II) Column I Column II (a) Chlamydomonas (i) Moss (b) Cycas (ii) Pteridophyte (c) Selaginell (iii) Algae (d) Sphagnum (iv) Gymnosperm

Solution:

Column I Column II

Chlamydomonas Algae

Cycas Gymnosperm

Selaginell Pteridophyte

Sphagnum Moss

12. Describe the important characteristics of gymnosperms. Solution: Characteristics of gymnosperms: a) Gymnosperm (Greek gymnos – naked, sperm – seed) are non-flowering seed plants. b) There are only 900 living species of gymnosperms, mostly distributed in colder areas. c) The plant body is a sporophyte, and can be differentiated into stem, leaves and roots. d) They are perennial trees and shrubs. Species of Gnetum are woodly climbers. e) Roots are tap root. In many cases, the roots form associations with algae (coralloid roots of cycas) and fungi (mycorrhizal roots of conifers). f) The stem is erect and aerial. The early stem is underground and tuberous in cycads. g) Leaves are dimorphic (two types), foliage and scale leaves. h) Conducting part of the xylem consists of tracheids. Vessels occur in Gnetum. i) Sporophylls are arranged to form strobili or cones. They are generally of two types – male cones and female cones. Male cones are short-lived, whereas female cones long-lived. j) Microsporangia are produced in microsporophyll. k) Megasporophylls are leaf-like in cycas and woody scale-like in conifers. l) Ovules are naked or exposed, sessile and unigamic. m) Integument is thick and differentiated into three layers – outer fleshy (sarcoteste), middle stony (sclerotesta) and inner fleshy. n) Microspores are produced in large numbers inside the microsporangia. They are liberated in 3-celled (Cycas), 4-celled (Pinus) and 5-celled (Ephedra) stages. o) All gymnosperms, except for gnetophytes, possess archegonia. The egg is comparatively large. p) Anemophily or wind pollination occurs in gymnosperms. q) The female gametophyte bears archegonia, provides nourishment to the developing embryo and later gets transformed into the endosperm (haploid) inside the seed. r) The seeds are naked or exposed on the surface of the megasporophyll.