Chapter 23: Plant Structure and Function...Plant Cells 55 and Tissues Apple cross section Leaf cross section Tree cross section Prepare Key Concepts This section focuses on the struc-ture

Chapter 23 OrganizerChapter 23 Organizer

Activities/FeaturesObjectivesSection

MATERIALS LIST

BioLabp. 646 microscope, microscope slide,coverslip, water, dropper, metric ruler,single-edged razor blade, leaf fromonion plant

MiniLabsp. 629 microscope, microscope slides,coverslips, water, dropper, celery stalkp. 640 microscope, microscope slides,coverslips, water, dropper, 5% salt solution, live plant leaf

Alternative Labp. 628 balance, garden trowel, water

Quick Demosp. 626 slices of apple, celery and pearp. 633 potato, iodine stainp. 643 potted houseplants

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

Teacher Classroom Resources

Assessment Resources Additional Resources

Products Available FromGlencoeTo order the following products,call Glencoe at 1-800-334-7344:CD-ROMNGS PictureShow: What ItMeans to Be GreenCurriculum KitGeoKit: PlantsTransparency SetNGS PicturePack: What It Meansto Be GreenVideodiscSTV: Plants

Index to NationalGeographic MagazineThe following articles may beused for research relating to thischapter:“Beyond Supermouse: ChangingLife’s Genetic Blueprint,” byRobert F. Weaver, December1984.

Teacher’s Corner

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Plant Structure and FunctionPlant Structure and Function

TransparenciesReproducible MastersSection

Plant Cells andTissues

Roots, Stems, andLeaves

Plant Responses

Section 23.1

Section 23.2

Section 23.3

Teacher Classroom Resources

Reinforcement and Study Guide, p. 101Concept Mapping, p. 23BioLab and MiniLab Worksheets, p. 105Content Mastery, pp. 113-114, 116

Reinforcement and Study Guide, pp. 102-103Critical Thinking/Problem Solving, p. 23BioLab and MiniLab Worksheets, p. 106Laboratory Manual, pp. 161-170Content Mastery, pp. 113-116

Reinforcement and Study Guide, p. 104BioLab and MiniLab Worksheets, pp. 107-108Content Mastery, p. 113, 115-116 L1

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Section Focus Transparency 55Reteaching Skills Transparency 32

Section Focus Transparency 56Basic Concepts Transparencies 36, 37

Reteaching Skills Transparencies 33, 34

Section Focus Transparency 57

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Assessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

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Chapter Assessment, pp. 133-138MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 23 quiz

Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations.

Plant Cells andTissuesNational Science EducationStandards UCP.1, UCP.2,UCP.5; A.1, A.2; C.1, C.5(1 session, 1/2 block)

Roots, Stems, andLeavesNational Science EducationStandards UCP.1, UCP.2,UCP.3, UCP.5; A.1, A.2; C.1,C.5 (1 session, 1 block)

Plant ResponsesNational Science EducationStandards UCP.1, UCP.2,UCP.5; A.1, A.2; C.1, C.5,C.6; G.1 (2 sessions, 1 block)

1. Identify the major types of plant cells.2. Distinguish among the functions of the

different types of plant tissues.

3. Identify the structures of roots, stems,and leaves.

4. Describe the functions of roots, stems,and leaves.

5. Identify the major types of plant hormones.

6. Analyze the different types of plantresponses.

Inside Story: A Plant, p. 628MiniLab 23-1: Examining Plant Tissues, p. 629Problem-Solving Lab 23-1, p. 630Investigate BioLab: Determining theNumber of Stomata on a Leaf, p. 646Art Connection: Red Poppy by GeorgiaO’Keeffe, p. 648

Problem-Solving Lab 23-2, p. 639MiniLab 23-2: Looking at Stomata, p. 640

Problem-Solving Lab 23-3, p. 644

Section 23.2

Section 23.2

Section 23.1

Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Animation: Water Uptake in Roots

Videodisc ProgramWater Uptake in Roots

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http://www.carolina.com

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Magnification:350�

Section

Types of Plant Cells Like all organisms, plants are com-

posed of cells. Plant cells can be dis-tinguished from animal cells becausethey have a cell wall, a central vac-uole, and can contain chloroplasts.Figure 23.1 shows a typical plantcell. Plants, just like other organisms,are composed of many different typesof cells.

ParenchymaParenchyma (puh RENG kuh muh)

cells are the most abundant kind ofplant cell. They are found through-out the tissues of a plant. Thesespherical cells have thin, flexible cellwalls. Most parenchyma cells usuallyhave a large central vacuole, which

23.1 PLANT CELLS AND TISSUES 625

The surface of a leaf or flowerreveals amazing complexitywhen viewed under a high-

power microscope. When you pick aflower or eat a piece of fruit, you maynot give its microscopic structure aminute’s thought. The structure of eachplant tissue is related to the function itperforms. For example, the epidermisof a tomato leaf with its covering of hairs helps protect the delicate tis-sues of the leaf from possible insect predators.

SECTION PREVIEW

ObjectivesIdentify the majortypes of plant cells.Distinguish amongthe functions of the dif-ferent types of plant tis-sues.

Vocabularyparenchymacollenchymasclerenchymaepidermisstomataguard cellstrichomexylemtracheidvessel elementphloemsieve tube membercompanion cellmeristemapical meristemvascular cambiumcork cambium

23.1 Plant Cells and Tissues

Figure 23.1 Plant cells have manydistinguishing fea-tures, such as a cellwall, chloroplasts,and a large centralvacuole.

Tomato plant leaves andfruit (top); glandular hairon leaf (inset)

Cell wall

Vacuole

Chloroplast

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Section 23.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 23,Section 23.1

What different types of tissues are found in these plants?

What is the function of these different tissues?

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SECTION FOCUS

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Transparency Plant Cellsand Tissues55

Apple cross section

Leaf cross section

Tree cross section

PrepareKey ConceptsThis section focuses on the struc-ture and function of plant cellsand tissues. The different typesof cells and their location in aplant are described. The sectionconcludes with a discussion ofplant tissues.

Planning■ Purchase apple, celery, and

pear for the Quick Demo.■ Assemble materials for the

Reinforcement.■ Purchase celery for MiniLab

23-1.■ Purchase or locate prepared

onion root tip slides for theInside Story.

■ Purchase onion leaves for theBioLab.

1 FocusBellringer Before presenting the lesson,display Section Focus Trans-parency 55 on the overhead pro-jector and have students answerthe accompanying questions.

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Assessment PlannerAssessment PlannerPortfolio Assessment

Assessment, TWE, pp. 627, 633Problem-Solving Lab, TWE, p. 644

Performance AssessmentAlternative Lab, TWE, p. 628-629MiniLab, SE, pp. 629, 640MiniLab, TWE, p. 629Problem-Solving Lab, TWE, p. 639Assessment, TWE, p. 644BioLab, SE, p. 646-647

Knowledge AssessmentSection Assessment, SE, p. 631, 641, 645Assessment, TWE, p. 645Chapter Assessment, SE, p. 649-651

Skill AssessmentProblem-Solving Lab, TWE, p. 630MiniLab, TWE, p. 640Assessment, TWE, pp. 641, 643BioLab, TWE, pp. 646-647

Plant Structure and Function

What You’ll Learn■ You will describe the major

types of plant cells and tissues.

■ You will analyze the structureand functions of roots, stems,and leaves.

■ You will identify plant hor-mones and determine thenature of plant responses.

Why It’s ImportantPlants are composed of cells,tissues, and organs. You needto be familiar with the struc-ture of plants so you can under-stand how they function andhow they respond to their envi-ronment.

Looking at Plant Organs Examine a potted plant. Whatdifferent plant organs are youable to identify?

To find outmore about

plants, visit the Glencoe ScienceWeb Site. www.glencoe.com/sec/science

23

GETTING STARTEDGETTING STARTED

ChapterChapter

As you look at this Africantulip tree, it is important to remember that plants are composed of individual cells such as the one in the inset photograph.

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Theme DevelopmentThe theme of systems andinteraction is apparent as theanatomy of roots, stems, andleaves is examined and the inter-dependence among these struc-tures is discussed. Homeostasisis stressed through the discussionof how plant hormones helpmaintain balance in plants.

Chapter 23Chapter 23

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Reinforcement, p. 627; Tech Prep, p. 635;

Activity, p. 636; Meeting IndividualNeeds, pp. 637, 638

Visual-Spatial Getting StartedDemo, p. 624; Microscope

Activity, pp. 627, 636, 638, 643;Portfolio, pp. 627, 636, 644; CulturalDiversity, p. 630; Meeting Individual

Needs, p. 640; Extension, p. 641;Quick Demo, p. 643

Interpersonal Project, p. 634

Linguistic Biology Journal, pp. 627, 639, 642; Reteach,

p. 645Logical-MathematicalEnrichment, p. 635

GETTING STARTED DEMOGETTING STARTED DEMO

Visual-Spatial Have stu-dents examine a potted

plant. Look at the plant’s roots,stems, and leaves. Ask studentsto suggest possible functionsfor each.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of theunit as an overview.

http://www.glencoe.com/sec/science

Plant TissuesRecall that a tissue is a group of

cells that functions together to per-form an activity. There are severaldifferent tissue types in plants. Eachone is composed of cells workingtogether.

Dermal tissuesThe dermal tissue, or epidermis, is

composed of flattened parenchymacells that cover all parts of the plant.It functions much like the skin of an animal, covering and protectingthe body of a plant. As shown in Figure 23.3, the cells that make upthe epidermis are tightly packed andoften fit together like a jigsaw puzzle.The epidermal cells produce the waxycuticle that helps prevent water loss.

Another structure that helps con-trol water loss from the plant, thestomata, are part of the epidermallayer. The stomata (STOH mut uh)are openings in the cuticle of the leafthat control the exchange of gases.Stomata are found on green stemsand on the upper and lower surfacesof leaves. In many plants, fewerstomata are located on the upper sur-face of the leaf as a means of conserv-ing water. Cells called guard cellscontrol the opening and closing ofthe stomata. The opening and clos-ing of the guard cells regulates theflow of water vapor from the leaf tis-sues. You can learn more about stom-ata in the BioLab at the end of thischapter.

The dermal tissue of roots mayhave root hairs. Root hairs are exten-sions of individual cells that help theroot absorb water and minerals. Onthe stems and leaves of some plants,there are structures called trichomes.Trichomes are hairlike projectionsthat extend from the epidermis andgive the epidermis a “fuzzy” appear-

ance. They help reduce the evapora-tion of water from the surface ofleaves. In some cases, trichomes areglandular and secrete toxic substancesthat help protect the plant frompredators. Stomata, root hairs, andtrichomes are shown in Figure 23.4.

Figure 23.3 The cells of the epi-dermis fit togethertightly to help pro-tect the plant andprevent water loss.

Figure 23.4 Root hairs are extensionsof individual cells on theroot (a). Trichomes arehairlike projections fromthe epidermis (b). Stomataare openings in the leaftissue surrounded byguard cells (c).

a

b

c

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Microscope ActivityVisual-Spatial Students cansee xylem cells under the

microscope if they prepare wetmounts of wood shavings fromthe pencil sharpener.

Portfolio Have studentsconstruct a table that includesboth the characteristics and func-tions of plant tissues. Have stu-dents place their completed tablein their portfolio.

ReinforcementKinesthetic Provide studentswith scissors, a dissecting

needle, tape, and several paperstraws. Ask them to use thesematerials to construct models ofvessel cells and sieve cells withtheir companion cells. Have stu-dents draw the nuclei on thestraw cells that contain them.Advise students that most xylemcells are dead and, therefore, lacka nucleus. Have students addlabels to the straw to identifyeach type. Models should have openends on vessels and closed ends withholes on sieve cells with a companioncell taped next to it.

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sometimes contains a fluid called sap,Figure 23.2A.

Parenchyma cells have two mainfunctions: storage and food produc-tion. The large vacuole found inthese cells can be filled with water,starch grains, or oils. The edible por-tions of many fruits and vegetablesyou eat are composed mostly ofparenchyma cells. Parenchyma cellsare also important in producing foodfor the plant. These cells containnumerous chloroplasts that produceglucose during photosynthesis.

CollenchymaCollenchyma (coh LENG kuh

muh) cells are long cells withunevenly thickened cell walls, as illus-trated in Figure 23.2B. The structureof the cell wall is important because itallows the cells to grow. The thinportions of the wall can stretch as thecell grows while the thicker parts ofthe wall provide strength and support.These cells are arranged in tubelikestrands or cylinders. The strands ofcollenchyma provide support for

surrounding tissue. The long toughstrands you may have noticed in celeryare composed of collenchyma.

SclerenchymaThe walls of sclerenchyma (skler

ENG kuh muh) cells are very thick andrigid. At maturity, these cells oftendie. Although their cytoplasm disinte-grates, their strong, thick cell wallsremain and provide support for theplant. Sclerenchyma cells can be seenin Figure 23.2C. There are two typesof sclerenchyma cells commonlyfound in plants: fibers and stone cells.Fibers are long, thin cells that formstrands. These strands provide sup-port and strength for the plant andare the source of fibers used in themanufacture of linen and rope. Stonecells are circular and usually found inclusters. They are responsible for thegritty texture of pears and are a majorcomponent of the pits found inpeaches and other fruits. Scler-enchyma cells are also a major part ofvascular tissue, which you will learnabout later in this section.

626 PLANT STRUCTURE AND FUNCTION

Figure 23.2Plants are composedof three basic typesof cells, which areshown stained withdyes here.

C23-06P

CollenchymaCell

OriginWORDWORD

par- From the Greekword para, meaning“beside.”

coll- From the Greekword kolla, meaning“glue.”

scler- From the Greekwords skleros, mean-ing “hard.”

With en meaning“in,” and chymeinmeaning “to pour.”Parenchyma, col-lenchyma, and sclerenchyma are alltypes of plant tissues.

Parenchyma cells are foundthroughout the plant. Theyhave thin walls and a large vacuole.

AA Collenchyma cells are oftenfound in parts of the plant thatare still growing. Notice theunevenly thickened cell walls.

BB The walls of sclerenchyma cellsare very thick. These dead cellsare able to provide support forthe plant.

CC

Magnification: 88� Magnification: 420�

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2 Teach

Quick DemoQuick Demo

Provide students with slices ofapple, celery, and pear. Pointout to the students that thesoft fleshy tissue of each speci-men is composed mostly ofparenchyma cells, the stringyfibers in the celery are com-posed of collenchyma cells,and the gritty particles in thepear are clusters of scleren-chyma cells.

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PortfolioPortfolio

Mapping Cells and TissuesVisual-Spatial Have students con-struct a concept map showing the

relationship between the different typesof plant cells and tissues. Have studentsinclude their completed concept map intheir portfolio.

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Building a PlantLinguistic Have students imaginethat they are going to build a plant

using traditional building materials suchas wood, brick, mortar, insulation, etc.Have them describe what materials theywould use to build each type of tissue inthe plant.

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MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

Learning DisabledHave students prepare a table to summarizethe characteristics of plant cells. Organizingthese characteristics into a table will help stu-dents with learning disabilities to distinguish

these cell types. Headings across the topcould include: Shape of cells, Nature of cellwall, and Function. Headings down the sideof the table should be: Parenchyma, Collen-chyma, and Sclerenchyma.

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The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INVESTIGATEINVESTIGATE

Resource ManagerResource Manager

Reteaching Skills Trans-parency 32 and Master

Concept Mapping, p. 23

BioLab and MiniLab Work-sheets, p. 105 L2

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Section Focus Transparency 55and Master

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Examining Plant Tissues Pipesare hollow. Their shape or structureallows them to be used efficiently intransporting water. Plant vasculartissues have this same efficiency instructure.

Procedure! Snap a celery stalk in half and

remove a small section of “stringy tissue” from its inside.@ Place the material on a glass slide. Add several drops of

water. Place a second glass slide on top. CAUTION: Usecaution when working with a microscope and slides.

# Press down evenly on the top glass slide with your thumbdirectly over the plant material.

$ Remove the top glass slide. Add more water if needed.Add a cover slip.

% Examine the celery material under low-and high-powermagnification. Diagram what you see.

^ Repeat steps 2-5 using some of the soft tissue inside thecelery stalk.

Analysis1. Describe the appearance of the stringy tissue inside the

celery stalk. What may be the function of this tissue?2. Describe the appearance of the soft tissue inside the cel-

ery stalk. What may be the function of this tissue?3. Does the structure of these tissues suggest their functions?

MiniLab 23-1MiniLab 23-1Vascular tissues

Food, minerals, and water aretransported throughout the plant byvascular tissue. Xylem and phloem arethe two types of vascular tissues.Xylem is plant tissue composed oftubular cells that transports water andminerals from the roots to the rest ofthe plant. In seed plants, xylem iscomposed of three types of scle-renchyma cells—tracheids, vessel ele-ments, and fibers. Parenchyma cellsare also present.

Tracheids are tubular cells taperedat each end that transport waterthroughout a plant. As you can see inFigure 23.5, both tracheids and ves-sel elements are cylindrical and deadat maturity. The cell walls betweenadjoining tracheids have pits throughwhich water and minerals flow.Conifers have tracheids but no vesselelements in their vascular tissues.

Vessel elements are tubular cellsthat transport water throughout theplant. They are wider and shorterthan tracheids. Vessel elements alsohave openings in their end walls. Insome plants, mature vessel elementslose their end walls and water andminerals flow freely from one cell toanother. Although almost all vascularplants have tracheids, vessel elementsare most commonly found in antho-phytes. This difference could be onereason why anthophytes are the most successful plants on Earth.Vessel elements are thought to trans-port water more efficiently than tra-cheids because water can flow freelyfrom vessel element to vessel elementthrough the openings in their endwalls.

You can learn more about how vas-cular tissues transport water in theMiniLab on this page. What othertypes of tissues are found in vascularplants? To answer this question, lookat the Inside Story.


Figure 23.5Tracheids and vessel ele-ments make up the xylem.The xylem transportswater and minerals fromthe roots, up the stem,and to the leaves.

Observing

Tracheid Vessel element

Purpose Students will use a squash tech-nique to prepare, observe, anddetermine the function of twoplant tissue types.

Process Skillsdraw a conclusion, interpret data,observe and infer, predict

Safety PrecautionsCaution students to be carefulwhile using a razor blade and tocut away from their bodies. Toreduce the possibility of injuryresulting from glass slide break-age during the squash technique,have students place several layersof paper toweling between theirthumb and the top glass slidebefore pressing down on theslide.

Teaching Strategies■ One grocery store celerybunch will be sufficient for allclasses.■ Provide students with single-edged razor blades or scalpels forcutting the celery.

Expected ResultsThe stringy tissue will appear asnongreen tissue that resembles atrack, or roadway. The soft tissuewill appear green and cubelike inshape.

Analysis1. tubelike, pipelike, stringlike,

nongreen or colorless; trans-port of materials

2. cubelike, square cells, greenin color; storage

3. Yes. Long, narrow cells areideal for transporting waterand nutrients. Cubelike cellswould be most suitable forfood storage.

Performance Have stu-dents observe other plant tissues.One possible activity is to prepareslide squashes of banana “strings”that remain on the fruit afterpeeling. Use the PerformanceTask Assessment List for MakingObservations and Inferences inPASC, p. 17.

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dividing the plant mass by the plantmass plus soil.

Expected ResultsThe fibrous roots should hold more soil inclose contact to its roots.Analysis

1. Based on your ratio, which root typeholds more soil in close contact to itsroots?

2. Which root type would have a greatersurface area for water absorption?

Performance Have studentswrite a lab report summarizing this lab.Use the Performance Task AssessmentList for Lab Report in PASC, p. 47.L3

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Terminal bud

Blade

Petiole

Vascular cambium

Stem

Leaves

Roots

Apical meristems

Flower

A Plant

There seems to be an almost endless variety of plants.Regardless of their diversity and numerous modifications,

all vascular plants have the same basic body plan. They arecomposed of cells, tissues, and organs.

Critical Thinking What are the different types of meristems andhow do they help the plant to grow new tissues and organs? House plants

INSIDESSTORTORYY

INSIDE

Organs The organsof a plant are thestem, leaves, androots. The stem holdsthe leaves. The leavesare the primary sitefor photosynthesis.The roots anchor theplant in the soil andabsorb water andminerals.

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Meristems Meristemsproduce new plant cells.The apical meristem pro-duces cells that increasethe height of the plant.The vascular cambiumproduces cells that resultin an increase in a stem’s diameter. The cork cambium producesthe outer layers of barkthat help to protect thestems and roots of woodyplants.

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Leaves The leaf of aplant is made up of ablade and petiole. Theblade contains cells filledwith chloroplasts. Theepidermis of a leaf hasstomata, which regulatethe movement of waterand gases between theinterior of the leaf andthe environment. Sugarthat is produced by pho-tosynthesis is transportedthrough the veins of theleaf to other parts of theplant. The petiole con-nects the leaf to thestem.

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Tissues There arefour types of plant tissues. Dermal tissueprovides a covering for the plant. Vasculartissue transports foodand water throughoutthe plant. Ground tissue produces andstores food. Meristemsproduce new cells.

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Purpose Students will study the basicbody plan of a plant.

Teaching Strategies■ Ask students to describe thefunctions of the four tissue types.

Visual Learning■ Ask students to bring in sam-

ples or pictures of leaves,stems, and roots. Have themdescribe the similarities anddifferences among the differ-ent organs.

■ Have students examine a pre-pared slide of an onion roottip. Point out that apicalmeristems produce new cellsthrough the process of mitosis.

Critical ThinkingApical meristems are located atthe tips of stems and roots. Theyincrease the height of the plantby producing new cells. The vas-cular cambium produces newphloem and xylem cells. Thecork cambium produces the outerlayers of bark.

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Alternative LabDifferences Between Taprootsand Fibrous Roots

Purpose This lab will allow students to compare tap-roots and fibrous roots.

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PreparationLocate areas where grass and dandelionsare growing.Materials garden trowel, metric balanceProcedureGive students the following directions.

1. Examine pictures of taproots andfibrous roots in your textbook. Whichtype of root do you think containsmore root hairs?

2. Using a trowel, loosen the soil arounda dandelion plant. Gently pull theplant out of the soil. Repeat thisprocess with a clump of grass.

3. Record the mass of each plant with itsclinging ball of soil. Carefully, rinseaway the soil under running water.Weigh and record the mass of theplants again.

4. Determine the ratio between plantmass and plant mass plus soil by 628

IINSIDENSIDESSTORTORYY

INSIDE MiniLab 23-1MiniLab 23-1

Terminal meristem

Shoot apical meristem

Root apicalmeristems

Lateral meristems

photosynthesis. Cells in the stem androot contain large vacuoles that storestarch grains and water. Cells, such asthose seen in Figure 23.7, are oftenseen in ground tissue.

Meristematic tissuesA growing plant needs to produce

new cells. These new cells are pro-duced in areas called meristems.Meristems are regions of activelydividing cells. Meristematic cells aresmall, spherical parenchyma cellswith large nuclei. There are severaltypes of meristems.

Apical meristems are found at ornear the tips of roots and stems. Theyproduce cells that allow the roots andstems to increase in length. Lateralmeristems are cylinders of dividingcells located in roots and stems.Figure 23.8 will help you visualizethe location of these meristems. Theproduction of cells by the lateralmeristems results in an increase indiameter. Most woody plants havetwo kinds of lateral meristems: a vas-cular cambium and cork cambium.The lateral meristem called the vascular cambium produces newxylem and phloem cells in the stemsand roots. The other lateral meristem,the cork cambium, produces a toughcovering for the surface of stems androots. The outer bark of a tree is pro-duced by the cork cambium.


Figure 23.7 The numerous chloro-plasts in this groundtissue produce foodfor the plant.

Figure 23.8The apical meristems arefound in the tips of the stemand roots. The vascular cam-bium extends the length ofthe stem and roots.

Section AssessmentSection Assessment

Understanding Main Ideas1. What are the distinguishing traits of the three

types of plant cells?2. What is the function of vascular tissue? What are

the two different types of vascular tissue?3. Explain the function of stomata.4. Draw a plant and indicate where on the plant

the apical meristems would be located. How dothey differ from lateral meristems?

Thinking Critically5. What type of plant cell would you expect to find

in the photosynthetic tissue of a leaf?

6. Compare and Contrast Compare and contrastthe cells that make up the xylem and the phloem.For more help, refer to Thinking Critically in theSkill Handbook.

SKILL REVIEWSKILL REVIEW


631

3 AssessCheck for UnderstandingQuiz students orally about thebasic characteristics of plant cellsand tissues.

ReteachWrite the following terms on theboard: storage, food production,support. Ask students to explainwhat types of cells and tissueswould carry out each function.

ExtensionAsk students what tissues ororgans in humans are analogousto plant tissues.

Skill Have students draw asimple diagram of a plant withroots, stems, and leaves. Havethem label the location of thefour types of plant tissues.

4 CloseDiscussionHave students explain what typesof plant cells they would find ineach of the following tissues: der-mal, ground, vascular, and meris-tematic. L2

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Section AssessmentSection AssessmentSection Assessment1. Parenchyma are spherical, thin-walled

cells. Collenchyma are cells with unevenlythickened cell walls. Sclerenchyma cellshave very thick cell walls.

2. Vascular tissue transports water, food,and minerals throughout the plant.Xylem and phloem are the two types ofvascular tissues.

3. Stomata control the flow of water vapor

from the leaf tissue.4. Apical meristems are found at the tips of

stems and roots. Lateral meristems in-crease stem and root diameter; apicalmeristems increase root and stem length.

5. parenchyma6. Xylem and phloem are both composed of

cylindrical cells. Xylem cells are dead atmaturity, whereas phloem cells are alive.

Sugars and other organic com-pounds are transported throughoutthe plant by the phloem. Phloem ismade up of a series of tubular cellsthat are still living and transports sug-ars from the leaves to all parts of theplant. The structure of phloem,Figure 23.6, is similar to xylembecause it is also composed of longcylindrical cells. However the phloemcells, called sieve tube members, arealive at maturity. Sieve tube membersare unusual because, although theycontain cytoplasm, they do not have anucleus or ribosomes. Next to eachsieve tube member is a companioncell. Companion cells are nucleatedcells that help manage the transportof sugars and other organic com-pounds through the sieve cells of thephloem. In anthophytes, the end wallsbetween two sieve tube members arecalled sieve plates. The sieve plateshave large pores. The sugar andorganic compounds move from cell tocell through these pores. Phloemtransports materials from the roots tothe leaves as well as from the leaves tothe roots.

The vascular tissue of many plantscontains fibers. Although the fibersare not used for transporting materi-als, they are important because theyprovide support for the plant. You canlearn more about vascular tissues inthe Problem-Solving Lab shown here.

Ground tissueGround tissue includes all tissues

other than the dermal tissues andvascular tissues. Ground tissue ismostly composed of parenchymacells but may also include col-lenchyma and sclerenchyma cells.The functions of ground tissueinclude photosynthesis, storage, andsupport. The cells of ground tissue inleaves and green stems containnumerous chloroplasts that carry on


What happens if vascular tissue is interrupted? Antho-phytes have tissues within their organs that transport materi-als from roots to leaves and from leaves to roots. What hap-pens if this pathway is experimentally interrupted?

AnalysisA thin sheet of metal was inserted into the stem of a

living tree as shown in the diagram. One day later, the following analysis of chemicals was made:■ Concentration of water

and minerals directly below the metal sheet was higher than water and minerals directly above the metal sheet.

■ Concentration of sugar directly above the metal sheet was higher than sugar concentration directly below the metal sheet.

Thinking Critically1. What is the function of phloem? Why was the concentra-

tion of sugars different on either side of the metal sheet?2. What is the function of xylem? Why was the concentra-

tion of minerals and water different on either side of themetal sheet?

3. How would the experimental findings have differed if themetal sheet were inserted only into the bark of the tree?

Problem-Solving Lab 23-1Problem-Solving Lab 23-1 Applying Concepts

Companion cell

Sieve plate

Sieve tube member

Figure 23.6 Phloem carries sugarsand other organiccompounds through-out the plant.

Higherwater andminerallevels

Highersugarlevels

Metalplate

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Purpose Students will determine thatwater and minerals move upwardthrough stems while sugar movesdownward through stems.

Process Skillsanalyze information, apply con-cepts, interpret data, predict, rec-ognize cause and effect

Teaching Strategies■ Review the nature of vasculartissue within the stem of antho-phytes but do not specificallymention the role of xylem andphloem.■ Point out to students thatmany trees are anthophytes.■ Diagrams may be consulted toshow that vascular tissue is con-tinuous through a plant’s stem.

Thinking Critically

1. Transports food downwardthrough plant; flow of sugarwas blocked above metalsheet, causing sugar to accu-mulate above the metal sheet.

2. Transports water and miner-als upward through plant;flow of water and mineralswas blocked by metal sheet,causing water to accumulatebelow the metal sheet.

3. Water and minerals wouldnot be blocked from flowingup the stem, but sugars wouldbe blocked above the metalsheet as phloem is locatedjust inside the bark.

Skill Ask students to writea hypothesis describing the exper-imental concentrations of water,minerals, and sugars 24 hoursafter inserting a metal sheet allthe way through the stem. Havethem predict the final outcome ifthe metal sheet were to remain in place across the tree’s stem. Usethe Performance Task AssessmentList for Formulating a Hypothe-sis in PASC, p. 21. L3

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Problem-Solving Lab 23-1Problem-Solving Lab 23-1

Cultural DiversityOrigin and Cultural Significance of Corn

Visual-Spatial Corn was one of theearliest crops to be domesticated, and

has been a major food source for NativeAmericans of both North and South Americafor about 7000 years. In addition to its

importance as a food source, corn also occu-pies a symbolic place in the culture of manyNative American tribes. Ask students work-ing in groups to research uses for corn otherthan as a food source. Ask each group toprepare an illustrated essay of its findings.

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Reinforcement and StudyGuide, p. 101

Content Mastery, p. 114 L1

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tall plants. Many climbing plantshave aerial roots that cling to objectssuch as walls and provide support forclimbing stems. Bald cypress treesproduce modified roots called pneu-matophores, which are often referredto as “knees.” The knees grow abovethe water upward from the mud andhelp supply oxygen to roots in water-logged areas.

The structure of rootsIf you look at the cross section of a

typical root in Figure 23.11, you cansee that the epidermis forms the out-ermost cell layer. A root hair is a tinyextension of a single epidermal cellthat increases the surface area of theroot and its contact with the soil.Root hairs absorb water, oxygen, anddissolved minerals. The next layer isa part of the ground tissue called thecortex, which is involved in thetransport of water and ions into thevascular core at the center of theroot. The cortex is made up ofparenchyma cells that sometimes actas a storage area for food and water.

At the inner limit of the cortex liesthe endodermis, a single layer of

23.2 ROOTS, STEMS, AND LEAVES 633

Figure 23.10Corn is a monocotwith shallow, fibrousroots. As the plantsgrow to maturity,roots called proproots grow from thestem to help keepthe tall and heavyplants upright.

Figure 23.11 The root structuresof dicots andmonocots differ inthe arrangementof xylem andphloem.

The xylem in a dicot root is arranged in acentral star-shaped fashion. The phloemis found between the points of the star.

AA In monocots, there are alternatingstrands of xylem and phloem that sur-round a pith of parenchyma cells.

BB

cells that forms a waterproof seal thatsurrounds the root’s vascular tissue.The waterproof seal between eachcell of the endodermis forces all waterand minerals to pass through the cellsof the endodermis. Thus, the endoder-mis controls the flow of water and dis-solved ions into the root. Just withinthe endodermis is the pericycle. Thepericycle is a tissue that gives rise tolateral roots. Lateral roots are rootsthat are produced as offshoots of


633

2 Teach

Portfolio Tell the studentsto imagine themselves as a dropof water trying to get from thesoil to the central vascular tissueof a root. Have them write a para-graph describing their journey.

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Section


RootsRoots are the underground parts

of a plant. They anchor the plant inthe ground, absorb water and miner-als from the soil, and transport thesematerials up to the stem. Some plants,

such as carrots, also accumulate andstore food in their fleshy roots. Thetotal surface area of a plant’s rootsmay be as much as 50 times greaterthan the surface area of its leaves. AsFigure 23.9 illustrates, roots may beshort or long, thick or thin, massiveor threadlike. Some roots evenextend above the ground.

Root systems vary according to theneeds of the plant and the textureand moisture content of the soil. Thetwo main types of root systems aretaproots and fibrous roots. A taprootis a central fleshy root with smallerbranch roots. For example, carrotsand beets are taproots. Fibrous rootsystems have numerous roots branch-ing from a central point. Figure 23.9shows examples of these root sys-tems. Some plants, such as the cornin Figure 23.10, have adventitiousroots called prop roots, which areaboveground roots that help support

The next time you eat salad, lookclosely at your plate. The carrotis a root, the celery is a leaf

stalk, lettuce is a leaf, and a beansprout includes stems, leaves, androots. Roots, stems, and leaves areorgans of plants and your salad con-tains several. There are more thanone-quarter million kinds of plantson Earth, and their organs exhibit anamazing variety.

SECTION PREVIEW

ObjectivesIdentify the structuresof roots, stems, andleaves.Describe the functionsof roots, stems, andleaves.

Vocabularycortexendodermispericycleroot capsink translocationpetiolemesophyll transpiration

23.2 Roots, Stems, and Leaves

Figure 23.9 The taproot of thecarrot can store largequantities of foodand water for theplant (a). The fibrousroots of grassesabsorb water andanchor the plant (b).

Salad of roots, stems, and leaves

a b

632

Section 23.2

PrepareKey ConceptsRoots, stems, and leaves are thefocus of this section. The func-tion of roots as water and mineralabsorbers is discussed. Next, thefunction of stems as conduits forwater and minerals is presented.Leaf structures are described asthey relate to photosynthesis.

Planning■ Purchase potato and iodine for

the Quick Demo.■ Purchase bromothymol blue

(BTB) solution and bean seedsfor the Project.

■ Find leaves for MiniLab 23-2.■ Purchase fertilizer and locate

film canisters for Tech Prep.■ Locate thin slices of tree trunk

sections for the Activity.


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What are the main parts of this tree?

What is the function of each part?

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Demonstrate starch storage inroot tubers by adding a fewdrops of an iodine stain to sev-eral slices of potato tuber.Explain that the blue-blackcolor indicates the presence ofstarch.

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VIDEODISCSTV: Plants, What Is a Plant?Unit 1, Side 1, 1 min. 40 sec.

Roots and Stems

!7Hm)h.É"


Section Focus Transparency 56and Master

Laboratory Manual, pp. 161-166 L2

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StemsStems are the aboveground parts of

plants that support leaves and flowers.Their form ranges from the thin,herbaceous stems of daisies, which dieback every year, to the massive woodytrunks of trees that may live for cen-turies. Green, herbaceous stems aresoft and flexible and usually carry outsome photosynthesis. Petunias, impa-tiens, and carnations are examples ofplants with herbaceous stems. Trees,shrubs, and some other perennialshave woody stems. Woody stems arehard and rigid and contain strands ofschlerenchyma fibers and xylem.

Stems have several important func-tions. They provide support for allthe aboveground parts of the plant.The vascular tissues that run thelength of the stem transport water,mineral ions, and sugars to and fromroots and leaves.

Like roots, stems are adapted tostoring food. This enables the plantto survive drought, cold, or seasonswith shorter days. Stems that act asfood-storage organs include corms,tubers, and rhizomes. A corm is ashort, thickened, underground stemsurrounded by leaf scales. The term“tuber” may refer to a swollen leaf or

stem. When used to refer to a stem, atuber is a swollen, underground stemthat has buds that will sprout newplants. Rhizomes are also under-ground stems that store food. Someexamples of these food-storing stemsappear in Figure 23.14.


Figure 23.13Roots develop by both celldivision and elongation. Asthe number and size ofcells increases, the rootgrows in length and width.

Figure 23.14 Plants can use food stored in stems to sur-vive when conditions are less than ideal.

Potato tubers are a kind ofunderground stem that sproutinto new potato plants.

AA

A corm of a gladiolus is athickened, undergroundstem from which roots,leaves, and flower budsarise.

BB

The rhizome of an iris isan underground stem.

CC

Root hairs

Xylem

Phloem

Pericycle

Endodermis

Root cap

Apical meristem

635

EnrichmentLogical-MathematicalHydroponics is an

agricultural process in whichplants are grown in a nutrientsolution rather than soil.Commercial hydroponics wasbegun in an attempt to reducefamine and eliminate the need forfarmers to contend with poor soilconditions and constant weatherchanges. Unfortunately, hydro-ponics has not worked well on alarge scale.

Ask students to researchhydroponics, make a list of all thenecessary nutrients and suppliesrequired for a hydroponics gar-den, and to evaluate the pros andcons of this growth method. L3

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Cortex

Root hair

Xylem

EndodermisPericycle Phloem

Endodermalcells Waterproof

seal


Figure 23.12Water and mineral ions move intothe root along two pathways.

Mineral ions and watermolecules enter root hairsand travel through thecells of the cortex byosmosis. Water also flowsbetween the cells of the cortex.

AA

Nutrients dissolved in water canflow between the parenchyma cells,directly into the root cortex, thenthrough the cells of the endodermis.

BB

older roots. Figure 23.12 traces thetwo pathways by which water andmineral ions move into the root.

Xylem and phloem are located inthe center of the root. The arrange-ment of this xylem and phloem tissueaccounts for one of the major differ-ences between monocots and dicots.In dicot roots, the xylem forms a cen-tral star-shaped mass with phloemcells between the rays of the star.Monocot roots have strands of xylemthat alternate with strands of phloem.There is usually a central core ofparenchyma cells in the monocotroot that is called a pith. The differ-ences between monocot and dicotroots are illustrated in Figure 23.11.

Root growthThere are two meristematic regions

in roots where growth is initiated bythe production of new cells. Recallthat meristems are areas of rapidlydividing cells. The apical meristem

produces cells that cause the root toincrease in length. As cells producedby the apical meristem begin tomature, they differentiate into differ-ent types of cells. The vascular cam-bium, which is located between thexylem and phloem, soon begins con-tributing to the root’s growth byadding cells that increase its diameter.

Each layer of new cells producedby the apical meristem is left fartherand farther behind as more new cellsare added and the root pushes for-ward through the soil. The tip ofeach root is covered by a tough, pro-tective layer of parenchyma cellscalled the root cap. As the rootpushes through the soil, the cells ofthe root cap wear away. Replacementcells are produced by the apicalmeristem so the root tip is neverwithout its protective covering.Examine Figure 23.13 on the follow-ing page to see if you can locate allthe structures of a root.

OriginWORDWORD

pericycle From the Greekwords peri, meaning“around,” and kykos,meaning “circle.” Invascular plants, thepericycle can pro-duce lateral roots.

endodermis From the Greekwords endon, mean-ing “within,” anddermis, meaning“skin.” In vascularplants, the endoder-mis is the layer ofcells forming theinnermost layer ofthe cortex in roots.

634

P R O J E C TDo Roots Respire?

Interpersonal Have student groups carryout the following experiment to answer

the question: Do roots carry out respirationand release carbon dioxide? Have studentsgerminate bean seeds and grow young plants(this takes about 10 days). Have studentsremove plants from soil and place the rootsinto tubes of bromothymol blue (BTB) solu-

tion. Have them seal the roots from the airusing a cotton or clay plug. Suggest that theyprepare a control tube . Advise students thatBTB turns from blue to light blue or green/yel-low in the presence of carbon dioxide. Havestudents observe the liquid 24 hours later. Askthem to write a report summarizing whatconclusions can be made regarding root tissuerespiration.

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CD-ROMBiology: The Dynamicsof Life

Animation: Water Uptake inRoots, Disc 3

VIDEODISCBiology: The Dynamicsof Life

Water Uptake in Roots (Ch. 22)Disc 1, Side 240 sec.!9@Ç"

Tying to PreviousKnowledgeHave students recall the differ-ences among facilitated diffusion,active transport, diffusion, andosmosis. If necessary, brieflyreview these concepts.

Which Fertilizers Work Best?Kinesthetic Use liquid fertilizer toprepare solutions of the following

percentages: 100, 80, 60, 40, 20, and 0.For preparation instructions, see page32T of the Teacher Guide. Assign eachstudent a different concentration. Havestudents plant seeds (turnip or mustard

seeds work well) in film canisters filledwith moist potting soil. Place film canis-ters in a warm sunny location or underfluorescent lights. Once a week, studentsshould add 5 mL of their assigned fertil-izer concentration. Students should watertheir plants as needed, make observa-tions of plant height and appearance,

and record observations in individual orclass journals. After several weeks, stu-dents should compile their observationsand draw conclusions about the effectsof varying amounts of fertilizer on plantgrowth.

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the roots to the leaves. The water thatis lost through the leaves is continu-ally replaced by water moving up thexylem. The water molecules form anunbroken column within the xylem.As this water moves up through thexylem, it also carries minerals that areneeded by all living plant cells.

Phloem transports sugars, miner-als, and hormones throughout theplant. The source of these sugars isphotosynthetic tissue, which is mostlyin the leaves in most kinds of plants.Any portion of the plant that storesthese sugars is called a sink, such asthe parenchyma cells that make upthe cortex in the root. The movementof sugars from the leaves through thephloem is called translocation (transloh KAY shun). Figure 23.17 showsthe movement of materials throughthe vascular tissues of a plant.

Growth of the stemPrimary growth in a stem is similar

to primary growth in a root. Thisincrease in length is due to the pro-duction of cells by the apical meristem,

which lies at the top of a stem. As men-tioned earlier, secondary growth or anincrease in diameter is caused by pro-duction of cells by the vascular cam-bium or lateral meristem. Additionalmeristems located at intervals along thestem give rise to leaves and branches.

LeavesThe primary function of the leaves

is to trap light energy for photosyn-thesis. Most leaves have a relativelylarge surface area so they can receiveplenty of sunlight. They are alsooften flattened, so sunlight can pene-trate to the photosynthetic tissuesjust beneath the leaf surface.

Leaf variationWhen you think of a leaf, you prob-

ably think only of a flat, broad, greenstructure known as the leaf blade. Infact, sizes, shapes, and types of leavesvary enormously. The giant Victoriawater lily that inhabits the rivers ofGuyana has leaves that may growmore than two meters in diameter.


Water moves up xylem

Water lostto air

Xylem

PhloemSourceof sugars

Sieve cell

Companion cell

Lateralroots

Sink

Figure 23.17Xylem carries waterup from roots toleaves. Phloemtransports sugarsfrom the source inthe leaves to sinkslocated throughoutthe plant.

The open ends of xylem vessel cellsform complete pipelike tubes.

AA Sugars in the phloem of this carrot plant are moving to sinks.

BB

637

EnrichmentThe neem tree is an anthophytethat grows in India and Thailand.The tree produces a flower with ahoney scent and fruit that resem-bles olives. The neem tree hasbeen called a “cornucopia tree”because of the diverse chemicalproducts made from it. The treeis used to make soap and oils forlubricants and fuel. It has alsobeen used to make an antimalar-ial agent.

The neem tree is also a power-ful insecticide. The tree wasfound to have a harmful effect onfleas, houseflies, head lice, gypsymoths, boll weevils, and cock-roaches. Today, chemicals fromthe tree are being marketed as ahome-and-garden insecticideunder the name Bioneem.

Have students research the useof other plants as natural insecti-cides. Ask students why insecti-cides derived from plants may bemore effective than those devel-oped by humans. L3

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Internal structure Both stems and roots have vascular

tissues. However, the vascular tissuesin stems are arranged differently fromthat of roots. Stems have a bundledarrangement or circular arrangementof vascular tissues within a surround-ing mass of parenchyma tissue. Asyou can see in Figure 23.15, mono-cots and dicots differ in the arrange-ment of vascular tissues in theirstems. In dicots, xylem and phloemare in a circle of vascular bundles thatform a ring in the cortex. The vascu-lar bundles of monocots are scatteredthroughout the stem.

Woody stemsMany conifers and perennial dicots

produce thick, sturdy stems, as shownin Figure 23.16, that may last severalyears, or even decades. As the stems ofthese plants grow in height, they alsogrow in thickness. This added thick-ness, called secondary growth, resultsfrom cell division in the vascular cam-bium of the stem. The xylem tissueproduced by secondary growth is alsocalled wood. In temperate regions, atree’s annual growth rings are the lay-ers of vascular tissue produced eachyear by secondary growth. Theseannual growth rings can be used todetermine the age of the plant. Thevascular tissues often contain scle-renchyma fibers that provide supportfor the growing plant.

As secondary growth continues, theouter portion of a woody stem devel-ops bark. Bark is composed of phloemcells and the cork cambium. Bark is atough, corky tissue that protects thestem from damage by burrowinginsects and browsing herbivores.

Stems transport materialsWater, sugars, and other organic

compounds are transported throughthe stem. Xylem transports water from


Figure 23.15 One of the primary differ-ences between roots andstems is that stems have thevascular bundles arrangedin a circular pattern.

Cork

Phloem

Annual Growth Rings

VascularCambium

Xylem

Figure 23.16The inner portion of the trunkof a tree is composed primarilyof dead xylem cells from thegrowth of the previous year.

The vascular bun-dles in a monocotare scatteredthroughout thestem.

AA

In young herbaceousdicot stems, discretebundles of xylemand phloem form aring. In older stems,the vascular tissuesform a continuouscylinder.

BB



636

ActivityKinesthetic Provide thinslices of tree trunk sections

to student groups. Have studentscount the rings to determine theage of their sample. Ask them tomark with a labeled pin the ringthat represents the year whenmost group members were born,assuming that the tree was cutthis year.

Microscope ActivityVisual-Spatial Preparedslides of root cross sections

are available from biological sup-ply houses. Allow students toview such slides to help thembecome familiar with the varioustissue names and their locations.Encourage students to sketchtheir observations.

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A Tree Has Good Years and Bad Years

Visual-Spatial Annual ring thickness isan indication of annual growing condi-

tions. For example, good growing conditionsyield a wider ring than years when condi-tions are poor. Have students use this infor-mation to make simple stylized diagrams of

a woody stem cross section that illustratesyears of both good and poor growth. Havethem label their diagrams to show whichring corresponds to which type of growingcondition. Encourage students to includeadditional labels that identify the generallocation of bark, phloem, cambium, andxylem.

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PortfolioPortfolio MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Visually ImpairedKinesthetic Construct a model leafblade from cardboard. Use straws

taped to the cardboard to represent leafveins and a piece of straw extendingbeyond the blade to represent the peti-ole. Allow visually impaired students tocompare the model to an actual leaf.

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VIDEODISCSTV: PlantsWoody Stem, Cross

Section Showing Rings

!7Xnt$"VIDEODISCSTV: PlantsWhat Is a Leaf?

Unit 5, Side 3, 14 min. 15 sec.What Is a Leaf? (in its entirety)

!9b&WftÇ"


Critical Thinking/ProblemSolving, p. 23 L3

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Stomata

Pore

Chloroplast

Epidermalcells

Guardcell

Thickenedwalls

Water

What factors influence the rate of transpiration? Plantslose large amounts of water during transpiration. This processaids in pulling water up from roots to stem to leaves where itis needed for photosynthesis.

AnalysisA student was inter-

ested in seeing if a plant’s surroundings might affect its rate of water loss. A geranium plant was set up as a control. A second gera-nium was sealed within a plastic bag and a third geranium was placed in front of a fan. All three plants were placed under lights. The student’s experimentaldata are shown in the graph.

Thinking Critically1. Which line, A, B, or C, might best represent the student’s

control data? Explain.2. a. Which line might best represent the data with the

plant sealed within a bag? Explain.b. What abiotic environmental factor was being tested?

3. Which line might best represent the data with the plant infront of a fan? Explain.

4. Write a conclusion for the student’s experiment.

Problem-Solving Lab 23-2Problem-Solving Lab 23-2 Drawing Conclusions


Figure 23.20 Guard cells regulate the size of theopening of the stomata according tothe amount of water in the plant.

AA

BB

CC

Wat

er lo

ss

Time

Rate of Water Loss

The guard cells have a thick-ened inner wall.

AA When water enters theguard cells, the pressurecauses them to bow out,opening the pore.

BB As water leaves the guardcells, the pressure is releasedand the cells sag together,closing the pore.

CC

mesophyll is made up of column-shaped cells containing many chloro-plasts. These cells are found just underthe upper epidermis, allowing formaximum exposure to the sun. Mostphotosynthesis takes place in the pal-isade mesophyll. Below the palisademesophyll is the spongy mesophyll,which is composed of loosely packed,irregularly shaped cells. These cellsare surrounded by many air spaces.These air spaces allow carbon diox-ide, oxygen, and water vapor to freelyflow around the cells. These gases canalso move in and out of the stomata,which are located in the dermal layer.

TranspirationYou read previously that leaves

have an epidermis with a waxy cuticleand stomata that help prevent waterloss. Guard cells are cells that sur-round and control the size of theopening in stomata, Figure 23.20.The loss of water through the stomata

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Purpose Students will analyze a graph andrelate it to factors that influencetranspiration rates.

Process Skillsanalyze information, compareand contrast, identify and controlvariables, design an experiment,draw a conclusion, hypothesize,interpret data, make and usegraphs, recognize cause andeffect, think critically

Teaching Strategies■ Students must be able to cor-relate sealing of a plant within aplastic bag with a correspondingrise in humidity within the bag.Discuss this idea with studentsprior to starting this activity.Based on their own experience,does perspiration evaporate fromtheir skin more quickly on ahumid day or a less humid day?■ Students must also be able tocorrelate presence of wind withan increase in water loss throughevaporation. Discuss this ideawith students prior to startingthis activity. Based on their ownexperience, why is it cooling tosit in front of a fan?

Thinking Critically

1. B; water loss from a fanwould be highest, water lossfrom inside plastic bag wouldbe lowest.

2. a. C; evaporation is reduceddue to high humidity withinthe bag.b. amount of humidity ormoisture in air

3. A; evaporation is accelerateddue to presence of wind.

4. A plant’s transpiration rate isrelated to environmental con-ditions. High humidityreduces the rate of transpira-tion. Windy conditionsincrease the rate of transpira-tion.

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Problem-Solving Lab 23-2Problem-Solving Lab 23-2The leaves of the tiny duckweed, acommon plant of ponds and lakes,are measured in millimeters. Ferns,pines, and flowering plants com-monly produce different forms ofleaves on the same plant.

Some leaves, such as grass blades,are joined directly to the stem. Inother leaves, a stalk joins the leaf bladeto the stem. This stalk, which is partof the leaf, is called the petiole (PET eeohl). The petiole contains vascular tis-sues that extend from the stem into theleaf to form veins. If you look closely,you will notice these veins as lines orridges running along the leaf blade.

Leaves vary in their shape andarrangement on the stem. A simpleleaf is a single leaf with a blade that isnot divided. When the blade is dividedinto leaflets, it is called a compoundleaf. Leaves also vary in their arrange-ment on a stem. When only one leaf ispresent at each point of the stem, theleaves are arranged in an alternate pat-tern. When two leaves are arranged inpairs along the length of the stem, theleaves form an opposite pattern. Thepairs of leaves may also alternate inposition along the stem formingopposite and alternate arrangements.Three or more leaves occurring atthe same place on the stem are saidto be whorled. Figure 23.18 givessome examples of the variety of leafshapes and arrangements.

Leaf structureThe internal structure of a typical

leaf is shown in Figure 23.19. Thevascular tissue of the leaf is located inthe veins that run through the midriband veins of the leaf. Just beneath theepidermal layer are two layers of mes-ophyll. Mesophyll (MEZ uh fihl) is thephotosynthetic tissue of a leaf. It isusually made up of two types ofparenchyma cells—palisade mesophylland spongy mesophyll. The palisade


StomataGuard cells

PhloemXylem

Vascularbundle

Palisademesophyll

Cuticle

Spongy mesophyll

Lower epidermis

Upperepidermis

Figure 23.18Leaf shapesvary, but mostare adaptedto receivesunlight.

Figure 23.19 The tissues of a leaf areadapted for photosyn-thesis, gas exchange,limiting water loss, andtransporting water and sugars.

The tulip poplar is adeciduous tree withbroad, distinctive, simple leaves.

CC

The arrangement of theneedlelike leaves of theevergreen yew allows themto receive the maximumamount of sunlight.

BB

The leaves ofthe walnut arecompoundwith manyleaflets.

AA

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Microscope ActivityVisual-Spatial Students canview prepared slides of leaf

cross sections. Have them com-pare the slides to the leaf crosssection in Figure 23.19. En-courage students to draw a dia-gram of the cross section andlabel the external and internalstructures of the leaf.

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A Leaf AnalogyLinguistic Ask students to describe in their journals how a cross-sectional

view of a leaf can be represented by a sand-wich. Ask students to describe the makeupof a sandwich and relate its componentparts to those in the leaf. To get started, tell them to compare the upper epidermisto the top slice of bread.

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VIDEODISCSTV: PlantsCell Layers of a Leaf,

Artwork

Transpiration, Artwork

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MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

Visually ImpairedKinesthetic Use two long, inflated bal-loons as a model of guards cells for

visually impaired students. Place the balloonsnext to each other. Typically, a bow will existin the center to simulate the stoma opening.

Allow students to examine the componentparts, guard cells and stoma opening, as youexplain what they represent. Push the twoballoons together to close the stoma andallow students to reexamine the model.

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Performance Have students performthis experiment. Ask them to prepare an out-line of their experimental procedure. Use thePerformance Task Assessment List forCarrying Out a Strategy and Collecting Datain PASC, p. 25. L2

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Basic Concepts Transparency36 and Master

Basic Concepts Transparency37 and Master

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Seed leaves Veins in leaves Vascular bundles Flower parts in stems

Monocots one usually parallel scattered multiples of cotyledon threes

Dicots two usually netlike arranged in ring multiples ofcotyledons fours and fives

Table 23.1 Distinguishing characteristics of monocots and dicots

Figure 23.22Modified leavesserve manyfunctions inaddition tophotosynthesis.


Understanding Main Ideas1. Compare and contrast the arrangement of xylem

and phloem in dicot roots and stems.2. In a plant with leaves that float on water, such as

a water lily, where would you expect to findstomata? Explain.

3. What is the primary function of most leaves?What are some other functions of leaves?

4. Explain how guard cells regulate the size of thestomatal pore.

Thinking Critically5. Compare and contrast the function and structure

of the epidermis and the endodermis in a vascu-lar plant.

6. Making and Using a Table Construct a tablethat summarizes the structure and functions ofroots, stems, and leaves. For more help, refer toOrganizing Information in the Skill Handbook.


Leaf modificationsMany plants have leaves that are

modified for functions other thanphotosynthesis, such as protectionand food storage. Cactus spines aremodified leaves that reduce waterloss and protect the plant from herbi-vores. A bulb is a short stem coveredby enlarged, fleshy leaf bases. Thefirst flowers of spring usually bloomfrom bulbs. The fleshy leaf bases ofonion and daffodil bulbs are modifiedfor food storage. The leaves of someplants are even modified to catchinsects. Examples of modified leavesare shown in Figure 23.22.

The leaves ofthis Aloe veraplant areadapted tostore water ina dry desertenvironment.

BB

The leaves ofthe pitcherplant are modi-fied for trap-ping insects.

AA

3 AssessCheck for UnderstandingHave students explain the differ-ence between the terms of thefollowing word groups.

a. transpiration—translocationb. palisade mesophyll—spongy

mesophyllc. guard cells—stomatad. epidermis—endodermis

ReteachHave students explain how thewords in each pair listed aboveare alike or related.

ExtensionVisual-Spatial Provide stu-dents with black line draw-

ings of cross sections of roots,stems, and leaves. Have studentslabel the drawings using termsfrom the text.

Skill Have students list ina table as many differences andsimilarities as possible betweenmonocots and dicots. Differencesshould center on vein patternsand differences in the pattern ofvascular bundles. Similarities aregeneral anatomy, multicellularity,and the ability to photosynthe-size.

4 CloseDiscussionHave students compare and con-trast the functions of roots,stems, and leaves. L1

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Looking at Stomata The lens-shaped openings in the epidermis ofa leaf allow gas exchange and helpcontrol water loss.

Procedure ! Make a wet mount by tearing a leaf

at an angle to expose a thin section ofepidermis. Use tap water to make wetmounts of both the upper and lower epidermis.

@ Examine each of your slide preparations under the micro-scope. Draw or take down a written description of whatyou see. CAUTION: Use caution when working with amicroscope, microscope slides, and coverslips.

# Make another wet mount using a 5 percent salt solutioninstead of tap water. Examine the slide under the micro-scope and record your observations.

Analysis1. What do the cells of the leaf epidermis look like? What is

their function? 2. How do the epidermal cells differ from guard cells? Which

cells, if any, contain chloroplasts?3. What differences in the stomata did you notice when you

used a salt solution to prepare your wet mount? Can youexplain what happened in terms of osmosis?

MiniLab 23-2MiniLab 23-2is called transpiration. You can learnmore about how a plant’s surround-ings may influence transpiration inthe Problem-Solving Lab on the previ-ous page.

The opening and closing of guardcells regulate transpiration. As youread about how guard cells work, besure to look carefully at the diagramsin Figure 23.20. Guard cells are cellsscattered among the cells of the epi-dermis. The inner walls of these cellsare thickened more than the outerwalls. When there is plenty of wateravailable in surrounding cells, guardcells take in water by osmosis. Whenwater enters, the thicker inner wallsprevent the guard cells from expand-ing in width, so they expand inlength. Because the two guard cellsare attached at either end, this expan-sion in length forces them to bow outand the pore opens. When water isnot readily available, there is lesswater in tissues surrounding the guardcells. Water leaves the guard cells,thus lowering their cell pressure. Thecells return to their previous shape,reducing the size of the stomatal pore.The proper functioning of guard cellsis important because plants lose up to90 percent of all the water they trans-port from the roots through transpi-ration. You can learn more about thestructure and function of stomata inthe MiniLab shown here.

Venation patternsOne way to distinguish among dif-

ferent groups of plants is to examinethe pattern of veins in their leaves.The veins of vascular tissue runthrough the mesophyll of the leaf. Asshown in Figure 23.21, leaf venationpatterns may be parallel, as in manymonocots, or netlike, as in mostdicots. Table 23.1 summarizes themany differences among the tissuesof monocots and dicots.

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Stomata

Figure 23.21Leaf venation patterns help distinguish between monocotsand dicots. Leaves of corn plants have parallel veins, a char-acteristic of many monocots (a). Leaves of lettuce plants arenet veined, a characteristic of many dicots (b).

Observing

a

b


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Purpose Students will observe stomataand determine how a salt solutionaffects stomata.

Process Skillsobserve and infer, compare andcontrast, use the microscope

Safety PrecautionsRemind students to be carefulwhen working with microscopes,glass slides, and coverslips.

Teaching Strategies■ Geranium, Coleus, or Trades-cantia leaves work well. If theseare unavailable, purchase freshspinach.■ The epidermis will appear as aclear strip of tissue at the jaggedtorn edge. Have students use thelower epidermis of the leaf.

Expected ResultsChloroplasts will be seen only inguard cells. The saltwater mountwill show closed guard cells.Thus, stomata will appear closedin comparison to the plain waterwet mount.

Analysis1. Cells look like interlocked

puzzle pieces. The cells areprotective.

2. Guard cells are sausage-shaped and have chloroplasts.Epidermal cells do not havechloroplasts and are irregularin shape.

3. Stomata are closed in the saltsolution. The higher waterconcentration inside the cellscompared with that outside ofthe cells caused water to moveout of the guards cells. Thiscauses the guard cells to col-lapse and close the stomata.

Skill Provide students witha diagram of leaf epidermis cells,guard cells, and stomata. Ask themto make a display in which theylabel each cell type and indicatewhich cells are capable of carryingout photosynthesis. Use thePerformance Task Assessment Listfor Display in PASC, p. 63. L2

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MiniLab 23-2MiniLab 23-2

MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Learning DisabledVisual-Spatial Have studentssequence the steps involved in

the opening and closing of stomata.Sequencing each step will help learn-ing disabled students to understandthe overall functioning of the stomata.

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Section AssessmentSection AssessmentSection Assessment1. In dicot roots, xylem forms a star-

shaped figure in the center withphloem between the star rays. Instems, xylem and phloem are arrangedin bundles that form a circle with thephloem outside of the xylem.

2. Stomata would be on the upper sur-face that is exposed to the air. This willallow for gas exchange with the air.

3. The primary function is to trap lightenergy for photosynthesis. Some aremodified for storage and protection.

4. When there is plenty of water, theguard cells swell and bow out, openingthe stomata.

5. The endodermis and epidermis bothcontrol the movement of water. Theendodermis is located within the root,

whereas the epidermis is the externalcovering of a plant.

6. Roots anchor the plant in the ground,absorb water and minerals and trans-port material up to the stem. Stemsprovide support and transport water,mineral ions and sugars to and fromroots and leaves. Leaves trap lightenergy for photosynthesis. 641

Resource ManagerResource ManagerBioLab and MiniLab Worksheets,

p. 106Reinforcement and Study Guide,

pp. 102-103Content Mastery, pp. 114-115Laboratory Manual, pp. 167-170 L2

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and allows the formation of branchesas they are no longer inhibited byauxins at the tip of the main stem,Figure 23.23. High concentrations ofauxin also promote fruit formationand inhibit the dropping of fruit fromthe plant. When auxin concentrationsdecrease, the ripened fruits of sometrees fall to the ground and deciduoustrees begin to shed their leaves.

Gibberellins promote growthThe group of plant hormones

called gibberellins (jihb uh REL uns)are growth hormones that causeplants to grow taller because, likeauxins, they stimulate cell elongation.Many dwarf plants, such as the dwarfbean plants in Figure 23.24, are shortbecause the plant either cannot pro-duce gibberellins or its cells are notreceptive to the hormone. If gib-berellins are applied to the tip of thedwarf plant, it will grow taller.Gibberellins also increase the rate ofseed germination and bud develop-ment. Farmers have learned to usegibberellins to enhance fruit forma-tion. Florists often use gibberellins toinduce flower buds to open.

Cytokinins stimulate cell divisionThe hormones called cytokinins

are so named because they stimulatecell division or cytokinesis. Cytokininsincrease cell division by stimulatingthe production of proteins needed formitosis. Most cytokinins are pro-duced in the meristems in the root.This hormone travels up the xylemto other parts of the plant. The effectof cytokinins is often enhanced bythe presence of other hormones.

Ethylene gas promotes ripeningThe plant hormone ethylene (ETH

uh leen) is a simple, gaseous com-pound composed of carbon and hydro-gen that speeds the ripening of fruits.

Figure 23.25 Tomatoes are usuallypicked when they aregreen. Once theyhave reached theirdestination, they aretreated with ethyl-ene. Most of the ripered tomatoes you seein the grocery storeshave been ripened inthis manner.

Figure 23.24 The bean plants inthis picture aregenetic dwarfs.However, the twoplants on the rightwere treated withgibberellin and havegrown to a normalheight.

OriginWORDWORD

auxin From the Greekword auxein, mean-ing “to increase.”Auxin causes stemelongation byincreasing cellgrowth

It is produced primarily by fruits, butalso by leaves and stems. Ethylene isreleased during a specific stage offruit ripening. It causes the cell wallsto weaken and become soft. Ethylenealso promotes the breakdown ofcomplex carbohydrates to simplesugars. If you have ever enjoyed aripe red apple you know that it tastessweeter than an immature fruit.

Many farmers use ethylene toripen fruits or vegetables that havebeen picked when they are immatureas shown in Figure 23.25.

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2 Teach

Skill Have students con-struct a table of the differenttypes of plant hormones and theireffects on plants.

Microscope ActivityVisual-Spatial Students canview the numerous cells in

various stages of mitosis in onionroot tip slides. Remind studentsthat cytokinins produced in theroot tip stimulate this cell divi-sion.

Performance Assessmentin the Biology Classroom, p. 47,Controlling the Rate at Which FruitRipens. Have students carry outthis activity to observe plant hor-mones at work. L2

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Section


Plant HormonesPlants, like animals, have hormones

that regulate growth and development.A hormone is a chemical that is pro-duced in one part of an organism andtransported to another part, where itcauses a physiological change. Only asmall amount of the hormone isneeded to make this change.

Auxins cause stem elongationThe group of plant hormones

called auxins (AWK sunz) promotecell elongation. Indoleacetic acid(IAA) is a naturally occurring auxinthat is produced in the apical meris-tems of a growing plant stem. Itcauses an increase in stem length byincreasing the rate of cell divisionand promoting cell elongation. IAAweakens the connections between thecellulose fibers in the cell wall. Thisallows the cells to stretch and growlonger. The combination of new cellsand increasing cell lengths leads tostem growth. Auxin is not transportedin the vascular system, but rather itmoves from one parenchyma cell tothe next by active transport.

Auxins have a number of other effectson plant growth and development.Auxin produced in the apical meristeminhibits the growth of side branches.

Removing the stem tip reduces theamount of auxin present in the stem

Plants cannot laugh or cry. They do notexhibit behaviors you commonly seein animals, but they do react to

their environment. They move in responseto light and gravity. The flowering headsof sunflowers can be seen to turn inresponse to the movement of the sun as itmoves across the sky. If a plant is growingin a dark forest and a tree falls allowing in more light, the plant will grow towards the light.

SECTION PREVIEW

ObjectivesIdentify the majortypes of plant hormones.Analyze the differenttypes of plant respon-ses.

Vocabularyhormoneauxingibberellincytokininethylenetropismnastic movement

23.3 Plant Responses

Figure 23.23Auxin from the tip of the main shootinhibits the growthof side branches (a).Once the main tip isremoved, the sidebranches start togrow (b).

Sunflowers

Shoot tip

Axillary budsinhibited

Axillary budsgrow intoside branches

Shoot tip removed

a b

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Section 23.3

PrepareKey ConceptsIn this section the major types ofplant hormones are described andtheir effects on plant growth arediscussed. Tropic and nastic plantresponses are explained.

Planning■ Locate onion root tip slides for

Microscope Activity.■ Obtain plants and gibberellic

acid for the Meeting IndividualNeeds - Gifted.


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To what stimuli is this plant responding?

Can this growth pattern be altered? Explain.

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Auxins and Stem ElongationLinguistic Ask students to write aparagraph explaining how auxin

causes stem elongation at the cellularlevel. Encourage students to draw picturesto illustrate their paragraph.

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Visual-Spatial Show students broadleaf

houseplants that have beenon a sunny windowsill. Askthem if they notice anythingspecial about the leaves.Direct their attention to theorientation of the leaves. Askstudents to propose ideas asto why the leaves are all fac-ing the same direction.P

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

GiftedHave students research and design anexperiment to test the effect of differentconcentrations of gibberellins on dwarfplants. Dwarf peas and the rosette varietyof Wisconsin Fast Plants work well for thistype of experiment.

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Resource ManagerResource ManagerSection Focus Transparency 57 and

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23.3 PLANT RESPONSES 645

Figure 23.27Mimosa pudica is alsoknown as the sensi-tive plant (a). Whentouched, it folds itsleaves in less thanone-tenth of a second.The Venus flytrap’shinged leaf snaps shutwhen triggered by aninsect crawling on itsleaf (b).


Understanding Main Ideas1. What is a hormone? 2. What are two differences between tropic

responses and nastic movements?3. Explain how a plant can bend towards the sun.

What term describes this response?4. Name one hormone and describe how it influ-

ences growth and development.

Thinking Critically5. One technique that has been used for years to

ripen fruit has been to put a ripened banana in a paper bag with the unripe fruit. Why does thishelp the unripe fruit to ripen?

6. Designing an Experiment Explain how youwould design an experiment to test the effect ofdifferent colors of light on phototropism in oneplant. For more help, refer to Practicing ScientificMethods in the Skill Handbook.


Some plants exhibit another tro-pism called thigmotropism, which isa growth response to touch. The ten-drils of the vine in Figure 23.26bhave coiled around a trellis aftermaking contact during early growth.

Because tropisms involve growth,they are not reversible. The positionof a stem that has grown severalinches in a particular direction cannotbe changed. But, if the direction ofthe stimulus is changed, the stem willbegin growing in another direction.

Nastic responses in plantsA responsive movement of a plant

that is not dependent on the directionof the stimulus is called a nasticmovement. An example of a nasticmovement is the folding up of the

leaflets of a Mimosa leaf when theplant is touched, as shown in Figure 23.27a. The folding is causedby a change in turgor pressure in thecells at the base of each leaflet. A dra-matic drop in pressure causes the cellsto become limp. This causes theleaflets to change orientation.

Another example of a nasticresponse is the sudden closing of thehinged leaf of a Venus flytrap, Figure 23.27b. The movement of aninsect on the leaf triggers the sensi-tive hairs on the inside of the leaf,causing the trap to snap shut. Plantresponses that are due to changes incell pressure are reversible becausethey do not involve growth. TheMimosa and Venus flytrap’s leavesopen once the stimulus ends.

a b 3 AssessCheck for UnderstandingHave students explain how thewords in each of the followingpairs are related.

a. auxin—hormoneb. cytokinin—cell divisionc. ethylene—ripe fruitd. tropic response—nastic

response

ReteachLinguistic Have studentswrite sentences correctly

using each of the groups of wordsin Check for Understanding.

ExtensionHave students do research on theuse of plant hormones in agricul-ture.

Knowledge Show stu-dents pictures of different plantresponses and ask them to iden-tify the type of response.

4 CloseBiology JournalAsk students to write a paragraphdescribing the relationshipbetween plant hormones andplant responses. L2

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How do plant stems respond to light? While workingwith young oat plants, Charles Darwin made a number of dis-coveries about the response of young plant stems to light. Hisdiscoveries helped to explain why plants undergo phototro-pism. Scientists now know that this response is the result ofan auxin that causes rapid cell elongation to occur along oneside of a young plant stem. However, the discovery of auxinswas not yet known during Darwin’s time.

AnalysisStudy the before and after diagrams marked A-C. The

three plants are young oat stems that are already aboveground. Note that the light source is directed at the plantsfrom one side.

Thinking Critically1. Which diagram (or diagrams) supports the conclusion that

light is a needed factor for phototropism? Explain.2. Which diagram (or diagrams) supports the conclusion that

the stem tip is a needed factor for phototropism? Explain. 3. Where might the auxin responsible for phototropism be

produced? Explain.

Problem-Solving Lab 23-3Problem-Solving Lab 23-3 Drawing a ConclusionPlant Responses

Why do roots grow down into thesoil and stems grow up into the air?Although plants lack a nervous sys-tem and usually cannot make quickresponses to stimuli, they do havemechanisms that enable them torespond to their environment. Plantsgrow, reproduce, and shift the posi-tion of their roots, stems, and leavesin response to environmental condi-tions such as gravity, sunlight, tem-perature, and day length.

Tropic responses in plantsIf you look at the photograph of

sunflowers at the beginning of this sec-tion, it is obvious that they are allresponding to the same stimulus—thesun. Tropism is a plant’s response toan external stimulus that comes froma particular direction. If the tropism ispositive, the plant grows toward thestimulus. If the tropism is negative, theplant grows away from the stimulus.

The growth of a plant towardslight is caused by an unequal distrib-ution of auxin in the plant’s stem.There is more auxin on the side ofthe stem away from the light. Thisresults in cell elongation, but only onthat side. As the cells grow, the stembends toward the light, as shown in Figure 23.26a. The growth of aplant toward light is called phototro-pism. You can learn more about pho-totropism in the Problem-Solving Labshown here.

There is another tropism associ-ated with the upward growth of stemsand the downward growth of roots.Gravitropism is the direction of plantgrowth in response to gravity.Gravitropic responses are beneficialto plants because the leaves receivemore light if they grow upward. Bygrowing down into the soil, roots areable to anchor the plant and can takein water and minerals.

Lightsource

Elongated cells

Figure 23.26Phototropism is thegrowth of a planttoward light (a).Thigmotropism is agrowth response totouch (b).

BeforeA B C A B C

After

Opaquecover

a

b

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Purpose Students will conclude fromexperimental evidence that lightand the tip end of a young stemare needed for phototropism.

Process Skillspredict, think critically, analyzeinformation, compare and con-trast, draw a conclusion, hypoth-esize, interpret data, recognizecause and effect

Teaching Strategies■ Explain to students that theseed in each diagram is below thesoil surface.■ Define the term “opaque” ifnecessary.■ Use the term “coleoptile” torefer to the young oat stem.

Thinking Critically

1. A and C; if there is no lightsource or the stem tip is notable to detect light, there isno phototropic response.

2. Student answers may vary.When the tip is intact (as inA), there is a phototropicresponse as the stem bendstowards light. However,when the tip end is missing,there is no phototropicresponse.

3. Stem tip end; when the tipend is removed, phototro-pism does not occur.

Portfolio Ask students todesign an experiment that wouldshow that the tip end of theyoung stem does indeed contain achemical that influences thebending of the stem toward light.Students should place their written experiment in their port-folio. Use the Performance TaskAssessment List for Assessing aWhole Experiment and Planningthe Next Experiment in PASC,p. 33. L3

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Problem-Solving Lab 23-3Problem-Solving Lab 23-3

PortfolioPortfolio

Plant ResponsesVisual-Spatial Have students collectpictures or drawings that show dif-

ferent plant responses. Have them glue ortape the pictures onto construction paperand write captions for each one. Studentsshould place their completed pictures ordrawings in their portfolios.

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Section AssessmentSection AssessmentSection Assessment1. A hormone is a chemical produced in

one part of an organism and trans-ported to another part, where it thencauses a physiological change.

2. Nastic movements are reversible,whereas tropic responses are not.Nastic movements are not dependentupon the direction of the stimulus,whereas tropic responses are.

3. A plant can bend towards the light asa result of cell elongation on the sideof the stem away from the light. Theterm phototropism describes thisresponse.

4. Possible answers: auxins cause stemelongation; gibberellins promotegrowth; cytokinins stimulate cell divi-sion; and ethylene gas promotes fruit

ripening.5. Ripe fruits release ethylene gas that

stimulates the ripening of other fruits.6. Expose the plant to red light for 24

hours and measure the response. Nextexpose the plant to blue light for 24hours. Continue testing until all avail-able light colors have been tested andcompare results. 645

Resource ManagerResource ManagerReinforcement and Study Guide,

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9. Move the slide to a different area.Count and record the number ofstomata in this field of view.Consider this trial 2.

10. Repeat step 9 three more times.Calculate the average number ofstomata observed in a high-powerfield of view.

11. Calculate the total number ofstomata on the entire onion leafby following the directions inData Table 2.

Going FurtherGoing Further

Application Carry out the same samplingtechnique to determine the total number ofstomata present on leaves of a variety of dif-ferent plant species in your neighborhood.

To find out more aboutplant anatomy, visit the

Glencoe Science Web Site. www.glencoe.com/sec/science

1. Communicating Compare yourdata with those of your otherclassmates. Offer several reasonswhy your total number of stom-ata for the leaf may not be identi-cal to your classmates.

2. Thinking Critically Analyze thefollowing steps of this experimentand explain how you can changethe procedure to improve theaccuracy of your data.a. five trials in Data Table 1b. using 0.07 mm2 as the area of

your high-power field of view3. Concluding Would you expect all

plants to have the same numberof stomata per high-power fieldof view? Explain your answer.

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Length of leaf portion in mm

Width of leaf portion in mm

Calculate area of leaf (length � width)

Calculate number of high-power fields of view on leaf (area of leaf � 0.07 mm2, thearea of one high-power field of view)

Calculate total number of stomata (numberof high-power fields of view � average number of stomata per high-power field of view from Data Table 1)

= _____ mm

= _____ mm

= _____ mm2

= _____

= _____

Data Table 2

4. Comparing and ContrastingWhat are the advantages to usingsampling techniques? What aresome limitations?

23.3 PLANT RESPONSES 647

Locate an area where guard cells and stomata can be clearlyseen. CAUTION: Use cautionwhen working with a micro-scope, microscope slides, and coverslips.

7. Switch to high-power magnifica-tion.

8. Count and record the number ofstomata in your field of view.Consider this trial 1. Record yourcount in Data Table 1.



1. mathematical errors, differ-ent average numbers of stom-ata, different leaf sizes

2. a. increase the number ofsamplesb. calculate microscope’shigh-power area

3. Different plants will have dif-ferent numbers of stomataper high-power field; stomatenumbers are characteristic forspecific plant species.

4. Saves time and energy; youdo not get an actual or truecount, only an approxima-tion.

Skill Provide students withsample data for leaf area andnumber of stomata per high-power field. Ask students to cal-culate the total number ofstomata. Use the PerformanceTask Assessment List for UsingMath in Science in PASC, p. 29.L3

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ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

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■ On occasion, the epidermis will tearwhen students scrape too vigorously.Have students discard their wet mountsand try a new sample of leaf material.

■ Failure to see or find any stomata may bedue to the fact that students did not placetheir leaf sample with the dark side down.Green onions do not have stomata ontheir inside surface.

Data and ObservationsStudent answers will vary. The number ofstomata will be several thousand.

Going FurtherGoing Further

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Determining the Number of Stomata on a Leaf

I f asked to count the total number of stomata on a single leaf, youmight answer by saying “that’s an impossible task.” It may not be nec-

essary for you to count each and every stomate. Sampling is a techniquethat is used to arrive at a close answer to the actual number. You will usea sampling technique in this BioLab.


PREPARATIONPREPARATION

3. Measure the length and width ofyour onion leaf in millimeters.Record these values in Data Table 2.

4. Remove a small section of leaf andplace it on a glass slide with thedark green side facing DOWN.

5. Add several drops of water andgently scrape away all green leaftissue using a back and forthmotion with the razor blade. Analmost transparent layer of leafepidermis will be left on the slide.

6. Add water and a cover glass to the epidermis and observeunder low-power magnification.

PROCEDUREPROCEDURE

1

2

3

4

5

Total

Average

Number of stomataTrial

Data Table 1

1. Copy Data Tables 1 and 2.2. Obtain an onion leaf and care-

fully cut it open lengthwise usinga single-edged razor blade. CAUTION: Be careful whencutting with a razor blade.

Problem How can you count the total num-

ber of stomata on a leaf?

Objectives In this BioLab you will:■ Measure the area of a leaf.■ Observe the number of stomata

seen under a high-power field ofview.

■ Calculate the total number of stom-ata on a leaf.

Materials microscope rulerglass slide glass coverwater and droppergreen leaf from an onion plantsingle-edged razor blade

Safety PrecautionsWear latex gloves when handling

an onion.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.


Time Allotment One class period

Process Skillscollect data, communicate, inter-pret data, recognize cause andeffect, draw a conclusion, com-pare and contrast, measure in SI,observe and infer, use numbers

Safety PrecautionsReview the need for care whenworking with single-edged razorblades. Remind students to cutaway from their bodies. Remindstudents that special care shouldbe taken when viewing slidesunder high-power so the objec-tive does not break the slide.Have students wash their handsafter handling plant materials.

Alternative Materials■ Any type of leaf may be substi-

tuted. Green onion is idealbecause it is inexpensive andeasily available in supermar-kets. It also is easily scrapedwith the razor blade to yield aclear epidermis.

■ Other leaves may beused. Students will have tocalculate the area of differ-

ently shaped leaves. Step 3 willno longer be valid if otherleaves are used. Geranium andFicus leaves also work well.

PREPARATIONPREPARATION

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PROCEDUREPROCEDURE

Teaching Strategies■ You may find that students will need touse a calculator.■ Review the procedure for determining anaverage.■ Students may want to know where thevalue of 0.07 mm2 came from. This value isclose to the area of the circle of light seenthrough high-power magnification.

■ You may wish to go through all of themath steps by using sample data on theoverhead projector.

Troubleshooting■ Students may have difficulty observing

the stomata. Most problems are the resultof not having scraped away enough of thespongy layer of the leaf.


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Chapter 23 AssessmentChapter 23 Assessment

SUMMARYSUMMARY

Section 23.1

Section 23.2

Section 23.3

Main Ideas■ Most plant tissues are composed of

parenchyma cells, collenchyma cells, and sclerenchyma cells.

■ Dermal tissue is a plant’s protectivecovering.

■ Xylem moves water and minerals upthe stem. Phloem transports sugarsand organic compounds throughoutthe plant.

■ Ground tissue often functions in food production and storage.

■ Meristematic tissues produce newcells.

Vocabularyapical meristem (p. 631)collenchyma (p. 626)companion cell (p. 630)cork cambium (p. 631)epidermis (p. 627)guard cells (p. 627)meristem (p. 631)phloem (p. 630)parenchyma (p. 625)sclerenchyma (p. 626)sieve tube member (p. 630)stomata (p. 627)tracheid (p. 629)trichome (p. 627)vascular cambium (p. 631)vessel element (p. 629)xylem (p. 629)

Plant Cells andTissues

Main Ideas■ Roots grow downward as cells elongate and

transport water and minerals from the root tothe rest of the plant.

■ The stem supports leaves and transports foodand water.

■ Leaves contain chloroplasts and performphotosynthesis.

Vocabularycortex (p. 633)endodermis (p. 633)mesophyll (p. 638)pericycle (p. 633)petiole (p. 638)root cap (p. 634)sink (p. 637)translocation (p. 637)transpiration (p. 640)

Roots, Stems,and Leaves

Vocabularyauxin (p. 642)cytokinin (p. 643)ethylene (p. 643)gibberellin (p. 643)hormone (p. 642)nastic movement (p. 645)tropism (p. 644)

CHAPTER 23 ASSESSMENT 649

2. Cambium and apical meristem are examplesof ________.a. photosynthetic tissuesb. protective tissuesc. growth tissuesd. transport tissues

Plant Responses

Main Ideas■ Three major plant hormones are auxins, gib-

berellins, and cytokinins. They promote celldivision and cell elongation.

■ Phototropism, gravitropism, and thigmotropismare all growth responses to external stimuli.

■ Nastic responses are caused by changes in cellpressure.

1. The tissue that makes up the protective cov-ering of a plant is ________ tissue.a. vascular c. groundb. meristematic d. dermal

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

649

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andactivities in the Interactive Tutor forBiology: The Dynamics of Life onthe Glencoe Science Web Site.www.glencoe.com/sec/science

1. d2. c

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS


All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.


Chapter Assessment, pp. 133-142MindJogger VideoquizzesComputer Test BankBDOL Interactive CD-ROM, Chapter 23

quiz

“When you take a flower in your hand and reallylook at it,” she said, cupping her hand and hold-ing it close to her face, “it’s your world for themoment. I want to give that world to someone

else. Most people in the city rush around so, theyhave no time to look at a flower. I want them to

see it whether they want to or not.”

American artist GeorgiaO’Keeffe attracted

much attention when thefirst of her many floralscenes was exhibited in NewYork in 1924. Everythingabout these paintings—theircolor, size, point of view, andstyle—overwhelmed theviewer’s senses, just as theircreator had intended.

In describing her huge paintings of solitaryflowers, Georgia O’Keeffe said: “I decided that Iwasn’t going to spend my life doing what hadalready been done.” Indeed, she did do what hadnot been done by painting enormous poppies,lilies, and irises on giant canvases. Her use of col-ors and emphasis on shapes suggests naturerather than copying it with photographic realism.Her work can be described as abstract. “I foundthat I could say things with color and shapes thatI couldn’t say in any other way—things that I hadno words for,” she said.

The viewer’s eye is drawn into the flower’sheart In this early representation of one of herfamiliar poppies, O’Keeffe directed the viewer’seye down into the poppy’s center, much as theflower naturally attracts an insect for reproduc-tion purposes. By contrasting the light tints ofthe outer ring of petals with the darkness of thepoppy’s center, the viewer’s eye is pulled, beelike,into the heart of the flower. The overwhelmingsize and detailed interiors of O’Keeffe’s flowers


ConnectionArtArt

Connection

Color plays a prominent role in the artistic effectof O’Keeffe’s flowers. What role does color playin the life of a real flower?

To find out more about GeorgiaO’Keeffe, visit the Glencoe

Science Web Site. www.glencoe.com/sec/science

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

give an effect similar to a photographer’s close-up camera angle.

During her long life of 98 years, GeorgiaO’Keeffe created hundreds of paintings. Hersubjects included the flowers for which she isperhaps most famous, as well as other botanicalthemes. She spent many years in New Mexico.Her paintings of the New Mexico deserts arecharacterized by sweeping forms, portraying sun-sets, rocks, and cliffs.

At the age of 90, she said of her success. “Ittakes more than talent. It takes a kind of nerveand a lot of hard, hard work.” She died in NewMexico in 1986. Georgia O’Keeffe will beremembered for her bold, vivid paintings thatare, indeed, larger than life.

Red PoppyO’Keeffe (1887–1986)

by Georgia

648

Purpose To illustrate the relationshipbetween nature and art.

Teaching Strategies■ Posters of O’Keeffe’s worksare available in art shops andmuseum gift shops. Bring in sev-eral examples to illustrate moreof her work. Have students visitan art gallery to view paintings byartists who use flowers as theirsubject matter. As an alternative,have students examine art booksto find the names of artists whouse flowers. Ask students to pre-sent oral reports on their find-ings.

Visual LearningAsk students what plant hormonemay have influenced the flower-ing of the red poppy.

Connection to BiologyOne possible answer is that colorattracts pollinators to the flowers.

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ConnectionArtArt

Connection

VIDEOTAPEMindJogger Videoquizzes

Chapter 23: Plant Structure and FunctionHave students work in groups as they playthe videoquiz game to review key chapterconcepts.




CHAPTER 23 ASSESSMENT 651

22. In late afternoon you are standing near a fieldof sunflowers. The flowers are all facing awayfrom you. Explain how you know which direc-tion they are facing.

23. Explain how the endodermis controls theflow of water and ions into the vascular tissueof the root.

24. Every spring, sap, a sugary fluid that travelsthrough phloem, is collected from sugar mapletrees to make maple syrup. Which type ofvascular tissue do the farmers tap into toremove the sap? Explain.

25. Comparing and Contrasting Compare andcontrast the flow of material through thexylem and phloem.

26. Recognizing Cause and Effect To allowsome trees to grow straighter, foresters mayremove surrounding trees by a process calledgirdling. To girdle a tree the forester removesa circle of bark from around the trunk of thetree. How does girdling eventually kill a tree?

27. Comparing and Contrasting Compare andcontrast apical and lateral meristems.

28. Concept Mapping Complete the conceptmap by using these vocabulary terms: xylem,tracheid, phloem, companion cell, sieve tubemember, and vessel element.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The graph below illustrates data on daisiescollected by scientists in four different states.Remember that stomata are the openings inthe leaves through which water vapor escapes.

Interpreting Data Examine the graph andanswer the following questions.1. In which state might there be the most

rainfall?a. state A c. state Cb. state B d. state D

2. In which state might there be the leastrainfall?a. state A c. state Cb. state B d. state D

3. How is rainfall correlated with numbersof stomata on leaves?a. the more stomata, the less rainb. the fewer the stomata, the less rainc. the more stomata, the more raind. the fewer the stomata, the more rain

4. Making a Graph Make a bar graph similar to the one above that shows howthe thickness of the leaf cuticle of a par-ticular plant varies from one state toanother. In state A, cuticles are thickest;state B, thinner than state A; state C,thicker than state B but not as thick asstate A; state D, thinner than state B.

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web Site.www.glencoe.com/sec/science

CD-ROM

Num

ber o

f sto

mat

a/le

af

State A State B

Origin of leaves

State C State D

Comparison of Numbers of Stomata

Sugars aretransported in

is composed of

Water istransported in

is composed of

2. 3. 5. 6.

1. 4.

651

23. The endodermis creates a barrierto the flow of water and ions,forcing them to flow throughthe endodermal cells. These cellscan then regulate the move-ment of these substances.

24. Phloem; Since sap contains su-gar, it is transported by thephloem.

25. Xylem and phloem both trans-port materials throughout theplant. Water and ions are trans-ported up the plant throughthe xylem. Water, sugars andother nutrients are transportedup and down the plant throughthe phloem.

26. Girdling interrupts the passageof nutrients in phloem cellsfrom leaves to roots. Roots areunable to receive food andeventually will die, resulting indeath of the tree.

27. Both types of meristems pro-duce new cells for growth. Theapical meristem is responsiblefor vertical growth. Productionof cells by the lateral meristemresults in an increase in girth.

28. 1. Phloem; 2. Companion cell; 3.Sieve tube member; 4. Xylem; 5.Vessel element; 6. Tracheid

THINKING CRITICALLYTHINKING CRITICALLY


1. a2. d3. c4.


3. Which of the following plant responses couldbe demonstrated by placing a potted plantnext to a sunny window?a. thigmotropism c. nastic movementb. phototropism d. gravitropism

4. A cross section of a root shows a central star-shaped mass of xylem when the plant is a(n)________.a. dicot c. annualb. monocot d. perennial

5. One of the primary structural differencesbetween roots and stems is the ________.a. arrangement of vascular tissue within the

stem and rootb. arrangement of pith within the stem and

rootc. differences in xylem and phloem functiond. differences in the numbers of stomata

6. What is the primary function of leaves?a. to provide protection for the plantb. to provide water for the plantc. to trap light energy for photosynthesisd. to enable the plant to grow taller

7. Which diagram correctly shows the function-ing of guard cells?

a.

b.

8. Water and mineral ions enter the root byabsorption into the ________.a. phloem c. stomatab. cuticle d. root hairs

9. Which of the following cells is a sclerenchymacell?a. meristematic cell c. vessel elementb. companion cell d. guard cell

10. The tissue that contains stomata is ________.a. vascular c. groundb. dermal d. meristematic

11. The movement of sugar through phloem iscalled ________.

12. The picture shown to the right is a ________ root.

13. The plant hormone that speeds up the ripen-ing of fruit is ________.

14. An analysis of the composition of the fluidtransported by the xylem tissue would revealthat it is mostly ________.

15. A dwarf plant can be induced to reach normalheight by the application of the hormone________.

16. The thin-walled cells that make up most ofthe ground tissue are ________.

17. Because the tip of a stem produces ________,removal of the tip stimulates lateral growth.

18. The portion of a plant that uses sugars isreferred to as a ________.

19. Apical meristems are found in the ________and ________.

20. The potato tuber is a type of ________.

21. Compare the expected rates of water move-ment in xylem tissues during the day and at night.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

650 CHAPTER 23 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Best TimesIf your test is timed, then practice under timedconditions. Try timing yourself on specific sectionsto see if you can improve your overall speed whilemaintaining accuracy. Do you notice an improve-ment in your score if you give yourself a fewmoments to double-check each answer? Learnfrom yourself.

Water

Water

650

3. b4. a5. a6. c7. b8. d9. c

10. b11. translocation12. dicot13. ethylene14. water15. gibberellin16. parenchyma17. auxins18. sink19. stem; root20. stem

21. Transpiration occurs mostrapidly during the day and aidsin the movement of waterthrough the xylem. Thus, watermovement is greater during theday than at night.

22. Since it is late afternoon, thesun will be in the west; theflowers will be facing westtowards the light source.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS


Comparison of Thickness of Cuticle

Origin of Leaves

Thic

knes

s of

Cut

icle

State AState B

State C

State D


Documents

Chapter 23: Plant Structure and Function...Plant Cells 55 and Tissues Apple cross section Leaf cross section Tree cross section Prepare Key Concepts This section focuses on the struc-ture