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Home , Ground tissue, Guard cell, Plant stem, Tissue (biology)

CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 616 CHAPTER Big nutrients. systems that absorb, transport, andstore and that absorb lightandcarry outphotosynthesis andtissue ONL 21.4 21.2 21.3 Online Bi Online ■■ ■■ ■■ ■■ ■■ ■■ 21.1 21 Absorption Spectra ofPlant Pigments Comparing Connecting Form to andRedLeaves QuickLab ofStomataDensity

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Q How would this compete with other species? Fig (Ficus) have a unique way of growing. Many trees of this genus are called strangler figs because their aggressive growth actually strangles other trees. Strangler figs can also wrap around unmoving objects such as these temple walls. Their germinate easily in tree or building cracks, and then snakelike roots grow down to the ground.

R e a d i N G T o o l b o x This reading can help you learn the material in the following pages.

USING LANGUAGE Your Turn Cause and Effect In biological processes, one step leads Identify the cause and the effect in the following sentences. to another step. When reading, you can recognize cause- 1. Some seeds float on the wind, so they are often found and-effect relationships by words that indicate a result, such far from the parent plant. as the words so, consequently, next, then, and as a result. 2. The substance that makes up plant walls is very strong. As a result, trees are able to grow very tall without breaking.

Chapter 21: Plant Structure and Function 617 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

21.1 Plant Cells and Tissues

5b, 10B, 10C key concept Plants have specialized cells and systems. VOCABULARY MAIN IDEAS cell Plant tissues are made of three basic cell types. collenchyma cell Plant organs are made of three tissue systems. sclerenchyma cell dermal tissue Connect to Your World You already know that besides roots, plants have stems (or trunks) and leaves. But did you know that these parts are considered the organs of the plant? Just like other organisms, plants have organs that are made of tissues, and tissues that are made of cells. It is easy to remember: plants have three main organs, made up of three tissue 5B examine specialized systems, mostly made up of three basic cell types. cells, including roots, stems, and leaves of plants...; 10B describe the interactions that occur among systems that perform the functions of transport, , and response in plants; 10C analyze the levels of organization in biological MAIN IDEA 5B systems and relate the levels to each other and to the whole system Plant tissues are made of three basic cell types. Plant cells are quite different from cells. In addition to all of the struc- tures that animal cells have, plant cells have cell walls, , and a large . Just as with , plants are made up of many types of cells that are CONNECT TO organized into tissues. Three basic types of plant cells, shown in FIGURE 1.1, are Cells parenchyma cells, collenchyma cells, and sclerenchyma cells. Recall from the chapter Cell Structure and Function that Parenchyma Cells plant cells differ from animal cells A parenchyma cell (puh-REHNG-kuh-muh)—the most common type of in having cell walls, , and large . Like animals, ­—stores , oils, and water for the plant. You can find paren- plants have different cell types. chyma cells throughout a plant. These cells have thin walls and large water- filled vacuoles in the middle. Photosynthesis occurs in green chloroplasts within parenchyma cells in leaves. Both chloroplasts and colorless plastids in parenchyma cells within roots and stems store starch. The flesh of many large vacuole we eat is also made of parenchyma cells. Parenchyma cells are sometimes thought of as the least specialized of plant cells, but they have one very special trait. They have the ability to divide throughout their entire , so they are important in wounds to the plant and regenerating parts. For example, parenchyma cells let you place stem cuttings of many types of plants in water to grow into a complete, new plant. Collenchyma Cells A collenchyma cell (kuh-LEHNG-kuh-muh) has cell walls that range from thin to thick, providing support while still allowing the plant to grow. These cells are most common in the younger tissues of leaves and . They often form into strands. For example, strings are strands of collenchyma cells.

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(l), (c), (r) ©Biophoto Associates/Photo Researchers, Inc. Plant organs systems. are ofthree made tissue ce Contrast FIGURE 1.1 FIGURE (magnification 150 (magnification ible cell walls that can change shape. Parenchyma cells have thinandflex- par

and chemical signals. Through plasmodesmata, the cells of aplant tissue can share water, nutrients, that pass through openings and walls incell connect living cells. connected by plasmodesmata (plaz-muh-DEHZ-muh-tuh), strands of complex tissues that have additional of types cells. Neighboring cells are often parenchyma, collenchyma, and sclerenchyma. may made They of be also tissue systems of plants may consist of simple tissues from types: basic cell the tissue is agroup of cells working together The tofunction. perform acertain systems inplants: dermal,ground, and tissue systems. that vascular a Recall Just as there are of three basic types plant cells, there are three groups of tissue Of the three basic plant cell types, a Sclerenchyma Cells grows, collenchyma cells can elongate and still give the leaf structure. don’twalls contain , so they are stretchy and can change size. As a young The unique feature of collenchyma cells is that are they flexible. Their cell . Humans use sclerenchyma cell fibers to make linen and . also found in stems and leaf veins and are responsible for the gritty texture of cells form a major part of pits and the hard outer shells of nuts. They are support for the water-conducting tissues or for the plant itself. Sclerenchyma of these dead cells disintegrate, but the rigid cell walls are left behind as skeletal vascular system, die when they reach maturity. The cytoplasm and lengthening anymore. Many sclerenchyma cells, such as those within the plant. Therefore, sclerenchyma cells are found in parts of the plant that aren’t makes these cells very rigid. Unlike collenchyma cells, they can’t grow with the lignin, which makes these cells very tough and durable. But the lignin also muh) is the strongest. These cells have a second cell wall that is hardened by lls different from one another? another? one from different lls MAI en N chyma ID

How are the cell walls of parenchyma, collenchyma, and sclerenchyma sclerenchyma and collenchyma, parenchyma, of walls cell the How are E

A Basic Plant Cell Types Cell Plant Basic 3

) 5B, 10B,5B, 10C co (magnification 250 (magnification range from thinto thick. Collenchyma cells have walls that ll sclerenchyma cell 5B en chy ma 3 ) (skluh-REHNG-kuh- (magnification 275 (magnification plant, even whenthecells die. and rigidwalls that the support Sclerenchyma cells have very thick scl e r en chy 3 ma ) Chapter are found, andtheirfunction. between plant cells, where they that organizes therelationship Make athree- chart TA Parenchyma elTp hr Function Where Cell Type

K R 21: I E N

Plant Structure andFunction I D A G G N OT N G E S TO B L O o x 619 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Dermal Tissue System Your body is covered with . Plants don’t have skin, but they do have a system of dermal tissue, shown in FIGURE 1.2, that covers the outside of a plant and protects it in a variety of ways. Dermal tissue, called , is made up of live parenchyma cells in the nonwoody parts of plants. On leaves and some stems, epidermal cells may secrete a wax-coated substance that becomes stem the cuticle. Dermal tissue made of dead parenchyma cells makes up the outer of woody plants. Ground Tissue System Dermal tissue surrounds the system of ground tissue, which makes up much of the inside of a plant. Ground tissue provides support and stores materials in roots and stems. In leaves, ground tissue is packed with chloroplasts, where photosynthesis makes food for the plant. The ground tissue system consists of leaf all three of the simple tissues—parenchyma tissue, collenchyma tissue, and sclerenchyma tissue—but parenchyma is by far the most common of the ground tissues. The ground tissue of cacti has many parenchyma cells that store water. However, the spines of cacti—which are actually modified leaves—contain mostly rigid sclerenchyma cells in their ground tissue. Vascular Tissue System Surrounded by ground tissue, the system of vascular tissue transports water, mineral nutrients, and organic compounds to all parts of the plant. Plants can transport necessary fluids and nutrients throughout their systems. A plant’s Dermal tissue vascular system is made up of two networks of hollow tubes somewhat like Ground tissue our veins and arteries. Each network consists of a different type of vascular Vascular tissue tissue that works to move different resources throughout the plant. Xylem (ZY-luhm) is the vascular tissue that carries water and dissolved mineral FIGURE 1.2 All three types nutrients up from the roots to the rest of the plant. Phloem (FLOH-ehm) is of tissue systems are found the vascular tissue that carries the products of photosynthesis through the throughout a plant. plant. You will learn more about the vascular system in the next section. Identify What tissue system contains the most photosynthesizing cells? 5b, 10c

Self-check Online HMDScience.com 21.1 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Describe three basic types of cells 3. Connect The dermal tissue system found within plants. 5B has been compared to . In 5. Plant cells have distinct 2. List two functions for each type of what ways does this analogy hold true? differences from animal cells, tissue system found in plants. 4. Compare What structures in the such as cell walls, large 10B provide a function vacuoles, and chloroplasts. similar to that of sclerenchyma cells How are these differences in plants? Explain. useful for a plant? 8C

620 Unit 7: Plants CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

©Andrew Syred/Photo Researchers, Inc. pressure-flow model pressure-flow theory cohesion-tension VOCABULARY other andto thewhole system systems andrelate thelevels to each levels oforganization inbiological response inplants; 10Canalyze the of transport, reproduction, and systems that perform thefunctions interactions that occur among plants...; 10Bdescribe the including roots, stems, andleaves of 5B examine specialized cells, synthesis ofnew molecules; transport ofmolecules, and , energy conversions, cellular processes, including bond hydrogen plant. that helps water move through a produce aforce called cohesion between water molecules negative . Hydrogen bonds hydrogen atom andaslightly between aslightly positive hydrogen bondisanattraction Chemistry ofLife that a Recall from thechapter H ydro CO 4Binvestigate andexplain NNE 21.2 gen B CT TO 4B, 5B,10B, 10C o n di hydrogen The Vascular System ng wat move through xylem. Water dissolved and minerals pump. How can itmove water upto aheightoftwo, three, oreven ten stories? tree roots all theway upto thehighestleaves. Butatree hasnoheart to act asa and removes wastes from them. In theworld are outside,fluids also moving from As you read this,your ispumpingblood, whichcarries nutrientsto your cells Your to World Connect ke

y xylem. So how do it? So xylem. do they The ends. The cells connect then end to end, forming long tubes. through When them. avessel element disintegrates wall dies, cell the at both FIGURE 2.1, (TRAY-kee-ihd). Tracheid cells, shown in of a complex tissue cells, xylem is called tissue. it contains Because types. basic cell the other types Xylemxylem. contains otherof types cells besides from roots the to rest the of plant the through lar tissue. Water and dissolved minerals move up that is one xylem Recall of of two the types vascu- Cohesion and adhesion create tension that moves water upward inxylem. by hydrogen bonds forming water between and molecules other substances. aremolecules attracted due also wall to to xylem the adhesion, aforce made waterbetween creates molecules aforce cohesion. called However, water another and to other surfaces. The tendency of hydrogen bonds to form on strong isthe supported based theory attraction of water to molecules one physical properties of water of allow rise water the through aplant. This well- wider than . avessel element.kind of called cell xylem Vessel elements are shorter and including most flowering plants, have an additional of plants, Some types vascular thick walls. cell tocell intracheids cell through openings inthe MAI MAI

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Amazin One t Phloem carries sugars from photosynthesis throughout theplant. Water anddissolved minerals move through xylem. N n N ID c ID ep are long and narrow. Water can flow from ype of specialized cell in xylem is called a is called inxylem cell ofype specialized E E t A AS gly, plants don’t any use to metabolic move energy water through

The vascular system allows for the transport of of transport the for allows system vascular The 4B, 5B, 10B, 5B, 10C4B,

Both types of types cells matureBoth and die before water moves

cohesion-tension theory Chapter 21:Plant Structure andFunction tracheid FIGURE 2.1 FIGURE SEM; magnification unknown) magnification SEM; are wider and shorter. (colored long, while vessel elements Tracheid cells are narrow and to-end throughout xylem. supporting cells that lie end- sel elements, conducting and co nsists of tracheids and ves- proposes that the

Xylem tissue element vessel

621 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

FIGURE 2.2 Movement of Fluids Through Xylem Biology HMDScience.com Forces responsible for the movement of fluids through xylem are transpiration, cohesion, adhesion, and absorption. GO ONLINE Movement Through a Plant

transpiration

water vapor

xylem

Transpiration is the evaporation of water through leaf stomata. It is the major force moving water through plants.

cohesion and adhesion Cohesion and adhesion create tension within xylem that helps move water upward. cohesion adhesion

absorption

Water and dissolved minerals in the soil are pulled into roots through cell walls, through plasmodesmata (channels), water or from cell to cell through their vacuoles.

CRITICAL What process is the main force for the VIEWING movement of fluids through xylem? Explain. 4B, 10B Transpiration

622 Unit 7: Plants bhspe-072102-006

Absorption bhspe-072102-009 DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

To understand how cohesion and adhesion affect xylem flow, imagine you R E ADI n g TOO LB ox are inside the cylinder of a xylem vessel. In the middle, the water molecules float freely, attracted to each other. Toward the edges, though, the molecules VOCABULARY The term cohesion comes from are also drawn to the xylem wall. Where the water meets the wall, this attrac- the Latin prefix co-, which tion draws it upward a bit so that the actual shape of the water surface is means “together,” and the term slightly concave. You can see this shape if you fill a test tube with water. The haerere, which means “to tendency of water to rise in a hollow tube is known as action. Capil­­ cling.” lary action causes water to rise above ground level in the xylem of plants. For most plants, capillary action is not enough force to lift water to the top branches. Upward force is also provided by the evaporation of water from VIRTUAL Lab leaves. The loss of water vapor from plants is called transpiration. As leaves HMDScience.com

transpire, the outward flow of water lowers the pressure in the leaf xylem, GO ONLINE creating a vacuum that pulls water upward. This force is responsible for most Plant Transpiration of the water flow in plants, including lifting water to the tops of trees. The movement of water through xylem is shown in Figure 2.2. Apply How does transpiration affect water movement through a plant?

MAIN IDEA 4B, 10B Phloem carries sugars from photosynthesis throughout the plant. The second tissue in a plant’s vascular system is phloem tissue, shown in FIGURE 2.3. Phloem carries plant nutrients, including minerals and sugars, FIGURE 2.3 Fluids move from the throughout the plant. Phloem moves the products of photosynthesis out of roots to the rest of the tree the leaves to stems and roots. Minerals that travel up the xylem can also move through the xylem. Phloem into the phloem through specialized parenchyma transfer cells in the leaves. carries the sugars produced by photosynthesis. Unlike xylem, phloem tissue is alive. Phloem is a complex tissue made mostly of cells called sieve tube elements. Their name comes from the small phloem holes in the end walls of their cells. These holes let the phloem fluids, or , flow through the plant. As they form, sieve tube elements lose their nuclei and ribosomes. Nutrients can then move from cell to cell. Each xylem is next to a companion cell, and the two cells are connected by many plas­ modesmata, or small channels. Because the companion cells keep all their organelles, they perform some functions for the mature sieve tube cells. In some plants, the companion cells help load sugars into the sieve tube cells. Recall that fluids in xylem always flow away from the roots toward the rest of the plant. In contrast, phloem sap can move in any direction, depending on the plant’s need. The pressure-flow model is a well-supported theory that explains how food, or sap, moves through a plant. Phloem sap moves from a source to a sugar sink. A source is any part of the plant that has a high concentration of sugars. Most commonly this source is the leaves, but it can also be a place where the sugars have been stored, such as the roots. A sink is a part of the plant using or storing the sugar, such as growing shoots and phloem stems, a fruit, or even the storage roots that will be a sugar source later in the season. The locations of sugar sources and sinks in a plant can change as the xylem plant grows and as the seasons change.

Chapter 21: Plant Structure and Function 623 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” 624

concentration. concentration to anarea oflower membrane from anarea ofhigh molecules across asemipermeable osmosis isthediffusion ofwater Structure andFunction that Recall from thechapter Cell O 21.2 Unit 7: Plants smosis CO 2. 1. Re

NNE pressure-flow model. a plant? ment ofwater through thexylem of transpiration involved inthemove- through thephl Describe how nutrientsare moved How are absorption and vi e CT TO wi Formative Assessment ng The the phloem. the movement ofsugars through FIGURE 2.4 FIGURE

4B, 10B oem according to the

pressure-flow model M ai 1 n I n p into thephloem. synthesizing leaves, source, suchasphoto- Sugars move from their d 3 e res 4B, 10B4B, they are stored. root orfruit,where suchasa the sink, The sugars move into as Apply in the directionin the of sink. the sure at end. sink the This difference inpressure sap keeps sugary flowing the plant. The overall result is higherpressure at source the end and lower pres- sugar into is unloaded Unloading sink. the sugars ATP uses also from the source. At samethe time, sugarthe concentration of end sink the is lessened as loading of sugars and passive flow of water creates pressure high at sugar the of sugars. Osmosis requires on of no energy part the plant. the This active flows into through phloem the osmosis, due concentration to high the source, there is alow concentration of water relative to sugars. Water then pump or sugar load into at phloem concentration. ahigh Therefore, at a keep nutrients moving through At phloem. asource, many plants ATP use to

sure-Flow Model sure-Flow The pressure changes sugar between sources and shown sinks, in

What are two plant parts that can be sugar sources? sugar be can that parts plant two are What explains 4. 3. C

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Analyze move?still Explain. Wouldof aplant. inthexylem fluids located only intheroots andstems Infer their functions? their functions? cells ofxylem andphloem suited for

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CO Explain. down through the phloem? xylem or moving nutrients moving water up through the en Which process requires more ll 2 ergy from the plant, NNE F HMDScience.com Self-check Online u the phloem. move sugars through The water flow helps sugars inthephloem. higher concentration of by osmosis, dueto the xylem into thephloem Water moves from the n CT TO ctio n 4B FIGURE 2.4, FIGURE

(l) ©Olga Shelego/ShutterStock; (t) ©Laurin Rinder/ShutterStock DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A G Online!

for the Sky!

VIRTUAL Lab BIOLOGY Web Plant Transpiration Movement Through a Plant Plant Learn Determine how different See how different materials move about adaptations that help environmental conditions through a plant. plants survive in their spe- affect the rate of cific environments. transpiration. ©Jan Halaska/Photo Inc. Researchers,

online biology 625 HMDScience.com CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” 626

FIGURE 3.1 FIGURE growth primary taproot root fibrous cap root hair root cylinder vascular VOCABULARY (LM; magnification 35 magnification (LM; some ofaroot. oftheparts of ar other andto thewhole system systems andrelate thelevels to each levels oforganization inbiological response inplants; 10Canalyze the of transport, reproduction, and systems that perform thefunctions interactions that occur among plants...; 10Bdescribe the including roots, stems, andleaves of 5B examine specialized cells, synthesis ofnew molecules; transport ofmolecules, and homeostasis, energy conversions, cellular processes, including data; 4Binvestigate andexplain inferences, andpredict trends from Unit 7: Plants oot tipcross-section shows 2Ganalyze, evaluate, make 21.3

This lightmicrograph 10 2G, 4B, 5B, 10B,  vascular cylinder ) apical meristem c Roots andStems root cap sy nutrients from soil. nutrients absorb mineral Roots and plants anchor the resources theplant needs,andeach plays part arole intheplant’s survival. height andwidth.Each ofaplant part grows inthedirection that allows itto reach growing theirentire lives. Woody plants, inparticular, can keep growing inboth Humans reach acertain heightandstop growing. Plants, however, can continue Your to World Connect ke

y stem of vascular plants. vascular of stem These cellsThese have tiny projections called plant absorbs most of its water tissue dermal inthe just above root the tips. is surrounded cylinder byvascular ground tissue, covered by tissue. dermal A which is made of and xylem tissues. phloem The woody rootswoody and stems, increase thickness the of plant these parts. apicalcalled (AY-pik-kul) . Lateral meristems, found along all into tissues. Areas of growth that lengthen tips the of roots and stems are cells aren’t but divide, specialized, they when some of cells specialize new the root cap, dermal. Parts of aroot are shown in three tissueall systems—vascular, ground, and store nutrients. other Like plant roots parts, contain supportRoots plant the and absorb, transport, and P minerals the plant needs. the ground, and from the soil they absorb water and half of the body of a plant. They anchor the plant to Why are roots important? Roots may make up over to area surface the available to up take water. Covering tip the of root the is the hairs way their find through greatly particles, soil spaces the between adding of cells that are source the of cells form new tissue called pushes through soil. the MAI MAI

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In center the of root the is the Jus Stems plants, support transport materials, andprovide storage. Roots anchorplants andabsorb mineral nutrients from soil. N n N t behind the roott behind the cap is where most of root’s the growth Groups occurs. ID c ID ept a small cone asmall of cells that protects growing the of part root the as it E E A AS

Roots and stems form the support support the form stems and Roots 4B, 5B, 10C 5B, 4B,

vascular cylinder, FIGURE 3.1. FIGURE root hairs, shown in

(colored SEM; magnification 80 magnification SEM; (colored loc FIGURE 3.2 FIGURE meristem. ated above theroot tip. FIGURE 3.2. FIGURE

Root hairsare Meristem Root Root  ) (bl) ©M.I. Walker/Photo Researchers, Inc.; (r) ©Andrew Syred/Photo Researchers, Inc. CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

(tr) ©AGStockUSA / Alamy; (cr) ©David Wasserman/Alamy Images E AA ANALSIS I LYS A N A DATA xplain received amountofsunlight. thesame seeds species,each They ofthesame sizepot. usedtypeandamountofsoil inthesame thesame for each Each plant. plant A group ofstudentscollected data ontheeffect ofwater ontheroot densitiesofbean plants. They planted three de Scientists needto includerepeated trials inexperiments inorder to draw reliable conclusions. Onefactor to consider when I taken uptaken as Fe for plant health. Even though only tiny amounts are minerals are these needed, necessary also amounts. Magnesium is amineral involved production in the of . mostly to catalyzeminerals reactions serve and are only needed intiny foressential mineral needed nucleic acids, , and chlorophyll. Other root causes cells also water to move into root the tip by osmosis. roots through active transport. The increased concentration of ions within ions. For example, nitrogen is often up taken as NO in water absorption. Mineral nutrients are usually dissolved water insoil as ment, and Their function. roots up take nutrients inaprocess that results also plantsAll require water and mineral nutrients certain for growth, develop- Water Uptake Mineral and plant to ground. the rootsThese spread like amat beneathsurface, soil the anchor and firmly the systems make branches fine inwhich most of roots the are same the size. one take Roots of two basic forms, as shown in T and beets areand beets examples of taproots that we eat. ground. The thick taproot sometimes can store also , Radishes, food. branches.smaller Long taproots allow plants to get water from inthe deep d ypes of Roots of ypes 30 mLofwater every other day inorder to produce themost roots. The studentsconclude that thisspeciesofbean plant should receive plants after 30days. Thegraph shows theresults oftheexperiment. Root density, thenumber ofroots percm • • • ­termining thenumberoftria ent

Som Plant Crec Plant Brec Plant Areceived 30mLofwater every day. 2. 1.

e How do root hairs help roots absorb water? absorb roots help hairs root How do improve theexperimental design? why not? Analyze ifyi e minerals are inlarge needed amounts. Nitrogen, for example, is an xperimenta ng t eived 30mLofwater every other day. eived 30mLofwater once aweek. 2+

Did thestudentsrea ions. Plants to transport energy use nutrient ions into the h e l Design im T aproot p or ls inanexperiment ishow muchvariation there isamongtheorganisms beingtested.

t How w systems have along, root thick, vertical with a n c 2G e ould you change the experiment to ch avalid conclusion? Whyor of

r epe 2 , was measured inall three a te FIGURE 3.3. FIGURE d t 3 – rials ions, and iron can be 4B Fibrous root Gra Root density 0 4 2 5 3 1 p h Chapter 21:Plant Structure andFunction ln ln Plant C Plant B Plant A 1. 1. FIGURE 3.3 FIGURE much smaller roots may . have onelarge taproot from which fibrous r roo Fibrous root oot systems. Radishes t d

T en Corn plants have aproot si t i e s

627 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” 628

a ring. shows vascular bundles forming section ofaherbaceous dicot scattered through Thecross- it. bundles ofvascular tissue shows ground tissue with cross-section ofamonocot stem from that inmonocots. The vascular tissue indicots differs Diversity that thepattern of Recall from thechapter Plant D M FIGURE 3.4 FIGURE runners, form new plants. stems; andstrawberry , or ginger are underground cacti; tubersstore starch; water, asdothefleshy stems of forms. Ba ico Unit 7: Plants o CO stolons Monocot n NNE t oco s obab tree trunksstore C

Baobab trees T Stems take various t

T s O

a n d

Dicot provide storage. materials, and transport plants, Stems support

ized andized end up of as part tissues the and organs of aplant. remain meristem cells for future divisions, others the while become special- plant. Meristem cells divide to create more cells. Some of divided cells the of plants is possible meristems because are active throughout the of the For as long as aplant it survives, is capable of growth. The continued growth Stem bark. An outer layer of bark provides aprotective covering. produced Phloem . near outside the forms of inner the the layer of structure. Sapwood, whichand is xylem conducts water, surrounds heart- the center Heartwood ofno longer atree trunk. conducts water but provides still example of stems. woody The oldest is in the of heartwood, part the xylem, the many broadleaf trees or or trees. — Tree are trunks an and may conduct photosynthesis. most do not grow than two meters. taller Herbaceous stems are often green ceous plants may monocots, be such as corn, or dicots, such as , and areThey do not they usuallybecause soft have many cells. Herba- xylem rigid potatoes and ginger are examples of stems that can grow underground. photosynthesize and store water. Although most stems grow above ground, can store or food water. The green stems of for cacti, example, can both shown in FIGURE3.4.Stems often house amajority system of vascular the and access to and sunlight. But stems have other functions as well, as You may know that stems support and leaves, giving better them MAI Ste Som N G ms can also be woody.ms be can also Most plants withstems woody are dicots, such as ID inger rhizomes G e stems are herbaceous. Herbaceous plants produce little or no wood. rowth E A

4B, 5 4B, b , 10B P otato

baobab tree ©Nick Garbutt/ Picture Library; cactus ©B.S.P.I./Corbis; strawberry stolons ©Dwight R. Kuhn; ginger ©Ron Chapple/Alamy Images; potato tubers ©TPH/Alamy Images; monocot ©Ed Reschke/Peter Arnold, Inc.; dicot ©Carolina Biological Supply Company/Phototake, Inc./Alamy Ltd CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

©Alan Linn/ShutterStock Summarize 21.3 2. 1. Re not available from any other records. scientific trees live thousands of years and can provide climate data that are thicker be ifthererings will were growing good conditions. Some growth. Climate, too, inferred can be from rings the since the growth and smaller, the darker bands cell of later season ring includes larger, the both lighter bands cell of spring annual rings. One ring represents one year of growth. Each appear they so darkerwalls, incolor. following months, cells are xylem and smaller have thicker light incolor. When water becomes more limited in the cells arexylem and wide have cells These appear walls. thin growth over seasons. In the spring, ifwater is plentiful, new found at ends the of stems and roots. growth takesplace inapical meristems tree rings, shown in growth responsible is also Secondary for formation the of T Secondary called grow or roots taller grow longer—is increases aplant’s length—makes stems ist dep trunk layers.trunk growth lifetimes.their takesplace inlateral Secondary meristems outer inthe Dicot trees, such and as , produce alot growth of over secondary stemsthe and roots of plants. woody

ree Rings are they similar? differ fr How ofstems dothefunctions are to important theplant. roo Describe two of majorfunctions ems within plant. the Growth that vi The a The pattern of plant growth ends on location the of mer the e ts. Explain whythese functions wi primary

ge of atreedetermined canby be counting these om those ofroots? How Formative Assessment ng How a

growth

growth. re tree rings formed? rings re tree

M adds to width the in FIGURE 3.5. FIGURE ai n I n This type ofThis type 10B d e as Tree rings form due to uneven 10B ­ 4. 3. C

ri

and stems. widens roots Secondary growth secondary growth ofatree? rhiz on the winter with littleprecipitation have Apply than roots? are they considered stems rather Analyze and stems. lengthens roots P VISUAL VOCAB VISUAL rimary growth t ical omes, grow underground. Why

primary growth and What effec

t Some stems, suchasginger hi nk i t could acold ng of growth one year bands Chapter 21:Plant Structure andFunction GO ONLINE GO heartwood 5. FIGURE 3.5 FIGURE wood in the center. non-functional, dark-colored dark band. Heartwood is the represented by a light and a bands. One year of growth is ducts water and grows in ored wood, sapwood, con- woody plants. The light-col- si

CO de protective covering of ring dating? this principle relate to tree key to the past.” How does past, or “The present is the events that occurred in the can be used to explain that can be observed today an The principle of uniformitari- t ism states that processes NNE h HMDScience.com Self-check Online ’ s sapwood C H T bark

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629 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 630 guard mesophyll blade VOCABULARY and to thewhole system and relate thelevels to each other organization inbiological systems plants; 10Canalyze thelevels of reproduction, andresponse in oftransport,the functions occur amongsystems that perform 10B describe theinteractions that , muscle, andepithelium; plants; andanimal cells suchas including roots, stems, andleaves of 5B examine specialized cells, synthesis ofnew molecules; transport ofmolecules, and homeostasis, energy conversions, cellular processes, including

7: 4Binvestigate andexplain

Plants 21.4 10C 4B, 5B, 10B, Leaves Most leaves structures. similar sharesome and retaining water intheirparticular environment. Plant specieshave theirown uniqueleaf shapes,specially adapted for gathering light people can identifymanyplants that are safe to eat—by theshapesoftheirleaves. how to avoid ivy. Hikers can identifypoisonous plants way inthesame that “Leaves ofthree, let itbe.” Thisisasaying ofmanyexperienced hikers whoknow Your to World Connect ke

y the sitethe of transpiration and . photosynthesis takesplace. The underside portion of aleaf has stomata and is upper portion of mesophyll the has most of chloroplasts the and is where most In most plants, top the and undersides of leaves have different functions. The CellsStomata Guard and dermal layers of a leaf is parenchyma tissue called from the plant. Between the two the inner tissues and limits evaporation resistant covering. The cuticle protects by a waxy cuticle that forms a water dermal tissue of many leaves is covered surrounded by ground tissue. The internal system of vascular tissue outer covering of dermal tissue and an Like roots and stems, leaves have an Leaf where a leaf ends. plant, called an axillary , marks between the petiole and the stem of a (PEHT-ee-ohl). A bud that grows basic parts. The common parts. Leaves grow out from a plant’s stem,Leaves and theyof differentare made up species of a don’tfew all look the same, but most leaves do share some out the mesophyll. The vascular tissues of xylem and phloem make up the veins that run through- stem by a thin stalk called the the plant. The blade connects to the and flat, and it collects the sunlight for MAI MAI

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Most leaves are specialized systems for photosynthesis. Most leaves share some similar structures. N n N T ID c ID issues ept E E A AS

Leaves absorb light and carry out photosynthesis. out carry and light absorb Leaves blade 4B, 5B, 10C 5B, 4B, is usually broad

petiole VISUAL VOCAB VISUAL The stem by a photosynthesis. Itconnects to theplant’s blade mesophyll petiole. ofaleaf collects sunlightfor (MEHZ-uh-fihl). petiole blade

©Mark A. Schneider/Photo Researchers, Inc. CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

guard cell, stoma ©Dr. Jeremy Burgess/Photo Researchers, Inc.; simple leaf, compound leaf ©Melba Photo Agency/Alamy Ltd; double compound leaf ©Runk/Schoenberger/Alamy Ltd; parallel veins ©Brian Tan/ShutterStock; pinnate veins ©Adam Hart-Davis/ Photo Researchers, Inc.; toothed margin, entire margin ©Melba Photo Agency; lobed margin ©Mark A. Schneider/Photo Researchers, Inc. Summarize wi Infer of theleaf margin—can beused to identifyplants. Certain leaf characteristics—such astheleaf type, thevein pattern, andtheshape 4.2 FIGURE Le concentration of K from neighboring cells accumulate guard inthe cells. Ahigh into asemicircle shape, opening stoma. the well. When plant the of water, is full two the guard cells plump up stomata. With stomata the plant closed, the may low run on CO gaining water at its roots, guard the cells deflate and closethe When plant the is losing water from transpiration faster than it is FIGURE 4.2, It is not always obvious what part of a plant is actually a leaf. As shown in Leaf Characteristics identify plants include the pattern of veins and the leaf edge, or margin. at the bases of the leaflets. Besides leaf shape, other traits of leaves used to single leaf because the is at the base of the petiole. There are no are called leaflets. All of the leaflets and their petiole together are actually a they may be compound, with many blades on one petiole. The multiple blades (CO stomata of most plants are open, allowing carbon the dioxide and c CO temperature, humidity, hormonal response, and amount the of for photosynthesis. The stomata closeat also night. Factors such as ndy environments? ndy a Simple leaf Whe A pair of

f t 2 in the leaves inthe guard the signal cells to open or close. How might compound leaves and leaves with lobed margins be well-suited to well-suited be margins leaves leaves lobed and with compound How might 2 ) necessary for) necessary photosynthesis to enter. ions (K an open and closeby changing shape. day, the During the y pe n the stomatan the are open, water evaporates from leaves. the Double compound leaf

leaves may be simple, with just one blade connected to the petiole, or Wha

Leaf Characteristics Leaf guard cells, t is the function of the guard cells of a plant? aplant? of cells guard the of function the t is + Compound leaf causes water to flow into guard the cells as shown in FIGURE 4.1, FIGURE l Pinnate veins Parallel veins e a

surround each stoma, f v e i n s + ) 2

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QUICKLAB analyzing Chlorophyll Fluorescence Materials If you remove chlorophyll molecules from their cells and then expose them to • mortar bright light, the energy absorbed from the excited electrons in the chlorophyll • pestle will be either lost as heat or released as a dull-colored light as the electrons • handful of spinach leaves return to their normal state. This is an example of fluorescence: the • 10 mL methanol absorption of light at one wavelength, and its release at a longer—and • graduated cylinder lower-energy—wavelength. • filter • funnel Problem How can fluorescence be used to study photosynthesis? • beaker Procedure • eyedropper or pipette 1. Use the mortar and pestle to crush a handful of spinach leaves, adding enough • test tube methanol to make 10 mL of extract. Use a graduated cylinder to collect and • test tube rack measure the extract. • flashlight 2. Place the filter paper in the funnel, and hold the funnel over a beaker. A second person should pour the extract through the funnel to filter the extract. 3. Carefully transfer the extract to a test tube, and hold it in front of a lit flashlight. Observe the fluorescence that occurs at a 90° angle from the beam of light. Analyze and Conclude 1. Identify What color does the fluorescence appear? 2. Analyze Why did the chlorophyll have to be extracted before the fluorescence could be observed?

MAIN IDEA 5B, 10B, 10C Most leaves are specialized systems for photosynthesis. The leaves of a plant are the main sites for photosynthesis. The broad, flat shape of many leaves allows for light gathering on the upper surface and gas exchange on the underside. Since the undersides of leaves are not exposed to direct sunlight, the plant loses less water while the stomata are open. Photosynthetic Structures There are two types of mesophyll cells in leaves, shown in FIGURE 4.3. Meso- R E ADI N G TO OLB ox phyll is the photosynthetic tissue of a leaf. Both types of cells in mesophyll TAKING NOTES have chloroplasts. Just under the dermal layer is a layer of tall, rectangular cells Use combination notes to called the palisade mesophyll. These cells absorb much of the light that enters describe and sketch each leaf the leaf. Beneath this layer is the spongy mesophyll. Spongy mesophyll has structure mentioned here. cells that are loosely packed, creating many air spaces. These air spaces con- Notes Sketch nect with the outside of the plant through the stomata, allowing carbon stomata dioxide and oxygen to diffuse in and out of the leaf. that the mesophyll plant makes move from mesophyll cells into phloem vessels, which carry the products to tissues throughout the plant.

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Leaf Adaptations Figure 4.3 leaf cross-section Not all leaves are “leafy.” Leaves are adapted This cross-section of a leaf shows the cuticle, dermal tissue, leaf veins for photosynthesis in the plant’s particular made up of xylem and phloem, and palisade and spongy mesophyll. environment. For example, cacti leaves are cuticle actually the sharp spines that protect them upper from predators and help minimize water loss epidermis due to transpiration. Other desert plants, palisade such as agave, store water in their leaves. The mesophyll leaves and stems of many desert plants are protected by very thick cuticles, which spongy minimize the loss of water from the plant. xylem mesophyll phloem Similar adaptations are common in coniferous trees in cold, dry climates. lower needles, for example, are leaves with a small epidermis surface area and a thick, waxy epidermis that protects them from cold damage. Tiny, sunken areas for the stomata help reduce stomata water loss. In comparison, water loss is not a problem for aquatic plants. The under- sides of a water lily’s leaves are below the water surface. To accommodate gas exchange in an aquatic environment, the water lily has stomata on the upper surface of its leaves. Many aquatic plants also have flexible petioles adapted to wave action. Many tropical plants have very large, broad leaves. In the crowded rain forest, the challenge is to get enough light and space among all the other plants. Larger leaves mean more light-gathering surface. Web

A few plants are actually predators. The pitcher plant, for example, has tall, HMDScience.com tubular leaves that help lure, trap, and digest insects. These insects provide GO ONLINE extra nitrogen for the plant, which is needed because there is little of it in the Plant Adaptations soil where the plant grows. Infer are also an of leaves. Their bright colors and fragrance attract animals and insects. Why is attracting other organisms important for some plants?

Self-check Online HMDScience.com 21.4 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Describe the functions of the blade 3. Infer The leaves of aquatic plants Analogous and petiole in a leaf. that are completely underwater have Structures 2. How do the palisade and spongy few stomata. Why might this be so? 5. The that allow pea mesophyll layers help a leaf perform 4. Apply Grass blades are leaves that plants to climb up an object photosynthesis? 5B are joined directly to the stem. What are modified leaves, whereas structure that is typical of many the tendrils of grape leaves is missing in grass? are modified stems. Explain.

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CHAPTER 21 G N I D A E R

F V each picture, andwrite caption. ashort shapes, lines,orarrows to illustrate Label themeaning.

the two terms ineach ofthefollowing pairs. Describe onesimilarity andonedifference between Compare andContrast R 21.1 vo Chapter 10. 11. 12. 13. or each word orpairofwords below, use simple 8. 6. 4. 2. 5. 9. 3. isualize 7. 1. eviewing

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phloem xylem vascular tissue ground tissue dermal tissue sclerenchyma cell col parenchyma cell lenchyma cell V Review ocabulary X O B L O O T tion l t, taproot c V e abu efix meaning “middle” isasuffix and-phyll ocabulary th, secondary growth ans “cellular tissue.” Explain how these d dermameans “skin.” How doesthis ascular tissue l, sclerenchyma cell merizein means “to divide.” How does lary Word Word O rig ins 21.3 21.2

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Photo ofthese gases into andoutofthe leaves? oxygen. How mesophyll does spongy play arole inthe help identifythespecies? How can xyl Describe similarities betw chloroplasts? is thistissue located, andwhydoesitcontain so many Some ground tissue c woody stems. type andexplain the traits that make thisso. exist inplant that parts are growing. still Identifythecell how these cells are specialized for these roles. support t support Both collenchyma andsclerenchyma cells provide Name two rol What can taproots dothat fibrous roots cannot do? Name three subst through xyl What processes are responsible for water flowing befor What musthappento tracheids andvessel elements t ability How isthestructure ofvascular tissue related to its dermal tis Describe onesimilarity andonedifference between the e they can inxylem? function synthesis requires andproduces HMDScience.com Interact 4B, 10B 4B 4B, 10B o transport materials intheplant? o a plant. Butonlyo aplant. oneofthese cell typescan sues innonwoody andwoody ofaplant. parts

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5B IDEAS ontains manychloroplasts. Where ophyll Chapter 21: Plant Structure andFunction Chapter 21: een herbaceous stems and 4B, 10B 4B, 10B 5B 5B

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Critical Thinking 26. Compare In animals, the term stem cells refers to Analyzing Data Evaluate Repeated Trials unspecialized or undifferentiated cells that give rise to An experiment was designed to test the effect of specialized cells, such as a blood cell. How are meristem various environmental factors on the successful germi- cells in plants similar to animal stem cells? 5B nation of grass . The control group of seeds was 27. Analyze A sugar beet plant develops a large root in the planted according to the directions on the seed packet. first year of growth and stores sugar in it until the Each of three additional groups tested one variable. The second growing season. But, besides sugar, as much as experimental design and results are shown in the chart three-fourths of the root’s weight can be water. Why is below. Use the chart to answer the next three questions. there so much water in the root? 4B, 10B Environmental Factors that Affect Grass 28. Apply In 1894, naturalist John Muir wrote about white Seed bark pines he saw at Yosemite National Park in California. Environmental Control Group A Group B Group C At high elevations, where there was snow on the ground Factor Group for six months each year, he studied a tree only three feet tall and six inches in diameter and determined it Hours daylight 12 6 12 12 was 426 years old. How did he know how old the tree Water 100% 100% 50% 100% was? Why might it be so small when trees of the same Temperature (°C) 24 24 24 12 species were much larger down the mountain? Seeds planted/ 5/5 5/5 5/1 5/3 29. Infer Many rain forest plants have leaves that taper to seeds germinated tips on the ends, called “drip tips.” Water from heavy rains drips off the tips of the leaves so that leaves below can absorb water as well. Why might this be an adaptive 34. Infer What do the data suggest about the conditions 4B, 10B advantage for the plant? under which grass seeds will or will not germinate? 30. Synthesize Use what you know about cohesion and 35. Evaluate Do the results seem logical? Explain. adhesion to explain why almost an entire sheet of paper towel can become wet even if only a corner of it is 36. Analyze If you could change anything in this experi- placed in water. 4B mental design, what would it be? Give at least two reasons to support your response. Interpreting Visuals Use the photograph to answer the next three questions. 31. Apply About how many years old was this tree when it Making Connections was cut down? 37. Write an Instruction Manual Imagine that you want to sell plant dissection kits. The kits will include instructions 32. Infer What does the pattern of growth rings indicate on where to find the basic structures of a certain plant, about the climate and the rate of growth of this tree such as the different type of cells and tissues, roots, over the years? leaves, stomata, stems, phloem, and xylem. First, decide what type of plant will be dissected. Then, write a set of 33. Predict Imagine this tree instructions to dissect the plant from the bottom up. were still growing. If the 5B next year had a spring with much less rain 38. Analyze Strangler figs were transplanted from the than previous springs tropics to states such as Florida and California because and then a summer of their unusual growth forms. Considering how they with a lot of sun- got their common name, why was this perhaps not a shine, what would good idea? the next growth ring look like? Explain. ©Alan Linn/ShutterStock

636 Unit 7: Plants Biology End-of-Course Exam Practice

Record your answers on a separate piece of paper. 4B, 9B MULTIPLE CHOICE 3 Plants capture radiant energy from sunlight and convert it to usable energy in the form of — 2G A carbon dioxide 1 B Tree Ring Growth from 1955 to 2005 C oxygen 0.8 0.7 D sugar 0.6 8C 0.5 0.4 4 What two structures do plant cells have that animal cells do not have? 0.3 A ribosomes and mitochondria

Tree ring width ring (mm) Tree 0.2 0.1 B mitochondria and cell walls 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 C chloroplasts and cell walls Years D chloroplasts and ribosomes Suppose a tree farmer has collected data about tree ring growth for many years. During that 8C time, only one major drought has occurred. 5 Which of the following characteristics is shared Based on the graph above, between which years by both plant cells and photosynthetic ? did the drought most likely occur? A cell wall of lignin A 1955–1960 B chlorophyll B 1965–1970 C DNA enclosed in a nucleus C 1975–1980 D vacuole for starch storage D 1990–1995 2E THINK THROUGH THE QUESTION 6 First, eliminate answer choices that list the years where there is no remarkable change in the graph. Ef fect of Nitrogen on Bean Plant Growth Then, consider the remaining choices. Would drought Trial 0% N 5% N 10% N 15% N have a negative or a positive effect on the width of a tree ring? 1 1.4 cm 2.2 cm 2.2 cm 3.6 cm 2 0.5 cm 2.6 cm 2.6 cm 2.6 cm 1.0 cm 3.6 cm 2.9 cm 3.5 cm 5B, 10C 3 2 Plant tissues are made of three basic types of cells: parenchyma, collenchyma, and sclerenchyma. Students recorded data on the effect of different Which of the following statements is true about percentages of nitrogen (N) in fertilizer on the these plant cells? growth of bean plants in centimeters. Fertilizer A Sclerenchyma cells grow with the plant. with no nitrogen was included in this experiment because it served as the — B Parenchyma cells make up the flesh of a peach, while sclerenchyma cells make up the pit. A model for the experiment C All three cell types have a . B control for the experiment D Collenchyma cells allow new plants to grow C independent variable for the experiment from stem cuttings, while parenchyma cells die D dependent variable for the experiment when they reach maturity.

Chapter 21: Plant Structure and Function 637