LAB TOPI C
19
Plant Anatomy
Laboratory Objectives
After completing this lab topic, you should be ableto:
I. Identify and describethe structureand function of eachcell type and
tFsue type.
2. Describe the organizationof tissuesand cells in each plant organ.
3. Relatethe function of an organ to its structure.
4. Describeprimary and secondarygrowth and identify the location of
eachin the plant.
5. Relateprimary and secondarygrowth to the growth habit (woody or
herbaceous).
6. Discussadaptation of land plants to the terrestrialenvironment asillustratedby the structureand functiono[ plant anatomy.
7. Apply your knowledge of plants to the kinds of produce you find in
the grocerystore.
Introduction
Vascularplants have been successfulon land for over 400 million years,
and their successis related to their adaptationsto the land environment.
An aquatic alga lives most often in a continuously homogeneousenvlronment: The requirementsfor life are everywherearound it, so relativelyminor
structural adaptationshave evolved for functions such as reproduction and
attachment.In contrast,the teffestrial habitat, with its extremeenvlronmentai conditions, presentsnumerous challengesfor the survival of plants.
Consequently,Iand plants have evolved structural adaptationsfor functions
such as the absorptionof undergroundwater and nutrients,the anchoring
of the plant in the substrate,the support of aerialparts of the plant, and the
transpoftation of materialsthroughout the relativelylarge plant body. In
angiosperms,the structuraladaptationsrequired for theseand other functions are divided among three vegetativeplant organs:stems,roots, and
leaves.Unlike animal organs,which are often composedof unique cell types
(for example,cardiacmusclefibersare found only in the heart, osteocytes
only in bone), plant organshave many tissuesand cell typesin common,
but they are organizedin different ways. The structural organizationof basic
tissuesand cell tlpes in different plant organsis directly related to their different functions. For example,leavesfunction as the primary photosynthetic organ and generallyhave thin, flat bladesthat maximize light absorption and gas exchange.Specializedcells of the root epidermisare long
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LabT opicl9 : Pl a n tAn a to my
extensionsthat promote one of the root functions,absorption.The interrelatlonshipof structureand function is a major themein biology,and you
wll continue to exploreit in this 1abtopic.
Use the figuresin this lab topic for orientationand as a study aid. Be certain that you can identify all items by examiningthe living specimensand
microscopeslides.These,and not the diagrams,will be usedin the laboratory evaluations.
Summary of BasicPlant Tissuesand Cell Types
Following is a review of plant tissuesand the most common typesof cells
will
seenin plant organs,aswell as their functions.Other specializedce11s
be describedas they are discussedin lab. Referback to this summary as
you work throughthe exercises.
Dermal Tissue: Epidermis
The epidermis forms the outermostlayer of cells,usually one cell thick,
coveringthe entire plant body. The epidermalcel1sare often flattenedand
rectangularin shape.Specializedepidermalcel1sinclude the guard cells of
the stomata,hairs calledtrichomes, and unicellular root hairs. Most eprdermal cellson abovegroundstructuresarecoveredby a waxy cuticle, which
preventswaterloss.The epidermisprovidesprotectionand regulatesmovement of materi.als.
Ground Tissue : Parenchyma, Collenchyma, and Sclerenchyma
Parench).rnacel1sare the most common cell in plants and are characterismay function in phototically thin-walled with largevacuoles.Thesece11s
s)'nthesis,suppofi, storageof materlals,and lateraltransporl.
Collenchyma cellsareusuallyfound near the surfaceof the stem,leafpetibut are
oles, and veins. Theseliving cells are similar to parenchymace11s
characterizedby an uneven thickening of cell walls. They provide flexible
support to young plant organs.
Sclerench;ana cellshave thrckenedcellwalls that may contain lignin. They
provide strengthand support to mature plant structuresand may be dead
at functional maturity. The most common type of sclerenchymacells are
1ong,thin fibers.
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Vascular Tissue: Xy1em and Phloem
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Xylem cel1sform a complex vasculartissuethat functions in the transport
of water and mineralsthroughout the plant and providessupport. Tiacheids
and vesselmembers arethe primary water-conductingcells.Tracheidsare
long, thin cellswith perforatedtaperedends.Vesselmembersare largerin
diameter,open-ended,andjoined end to end, forming continuoustranspoft
cellsarepresentin the xylem and
systemsreferredto asvessels.Parench).'rna
ln the xylem provide addiFibers
lateral
transport.
in
and
function storage
(Color
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Phloem tissuetransportsthe products of photosynthesisthroughout the
plant aspart of the vasculartissuesystem.This complextissueis composed
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LabTopi cl 9: P l an rAnat om \ 503
of llving, conductingcellscalledsieve-tubemembers,which lack a nucleus
and havesieve plates for end walls. The cellsarejoined end ro end throughout the p1ant.Each sieve-tubemember is associatedwith one or more
adjacentcompanion cells, which are thought to regulatesieve-tubemember function. Phloemparench;rrna
cellsfunctionin storageand lateral[ranspoft, and phloem fibersprovide additional suppon (Color Plate57).
Meristematic Tissue: Primary Meristem and Cambium
Primary meristems consist of small,activelydividing cellslocatedin buds
of the shoot and in root tips of plants.Thesecel1sproducethe primary tissuesalong the plant axis throughout the iife of the plant.
Vascularcambium is a lateralmeristemalsocomposedof small,activelydividing cells that are located betweenthe xylem and phloem vascularrissue.
Thesecel1sdivide to producesecondarygrowth,which resultsin an lncrease
in slrth.
E X E R C IS E
19.1
Plant Morphology
Materials
living bean or geranium plant
squirt bottle of water
paper towel
Introduction
As you beginyour investigationof the structureand function of plants,you
need an understandingof the generalshapeand form of the whole plant.
ln this exercise,you will study a bean or geraniumplant, rdentilyng basic
features
oI the lhreevegetative
organs:roots.st-ems.
and leaves.
In the following exercises,you will investigatethe cellularstructureof theseorgans
as viewed in crosssec[ions.Referto the living plant for orientationbefore
you view your slides.
Procedure
1. Working with another student, examinea living herbaceous(nonwoody) plant and identily the following structuresin the shoot (stems
and leaves):
a. Nodes areregionso[ the stemfrom which leaves,buds,and branches
ariseand which con[ain merisrematictissue(areasof cell division).
b. Internodes are the reglonsof the stem locatedbetweenthe nodes.
c. Terminal buds are locatedat the tips of stemsand branches.They
enclosethe short apicalmeristem,which givesrise to leaves,buds,
and all primary tissueof the stem.Only stemsproducebuds.
d. Axillary, or lateral, buds are locatedin the leaf axesat nodes;they
may give rise to lateralbranches.
e. Leavesconsis[of flattenedblades attachedat the node of a stemby
a stalk, or petiole.
504
Lab Tooic 19: Plant Anatomv
2. Observethe root structuresby gently removingthe plant from the pot
and looseningthe soil from the root structure.Youmay needto rinsea
few roots with water to observethe tiny, active roots. ldentify the following structures:
a. Primary and secondary roots. The primary root is the first root producedby a plant embryoand may becomea long iaproot.Secondary
roots arisefrom meris[ematictissuedeepwithin the primary root.
b. Root tlps consistof a root apical meristem that givesrise to a root
cap (protectivelayer of cellscoveringthe root tip) and to all the primary tissuesof the root. A short distancefrom the root tip is a zone
of root hairs (specializedepldermalcells),the principal siteof water
and mineralabsorption.
Results
I . LabelFigureI 9.1.
Z. Sketch in the margin of your lab manual any featuresnot included in
this diagramthat might be neededfor future reference.
Figure 19.1.
A herbaceous plant. The vegetative
plant body consistsof roots, stems,
and leaves.The buds are located in the
axils of the leavesand at the shoot tip.
The roots also grow from meristem tissuesin the root tip. Label the diagram
based on your observationsof a living
plant and the structures named in
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Lab Topic 19: PlantAnatomy 505
Discussion
1. Look at your plant and discusswith your pailner the possiblefunctions
of eachplant organ.Your discussionmight include evidenceobserved
in the lab todayor prior knowledge.Describeproposedfunctions(more
than one) for eachorqan.
Stems:
Roots:
Leaves:
2. Imagine that you have cut each organ-roots, stems,and ieaves-rn
crosssection.Sketchthe overallshaneof that crosssectionin the mar*,
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E X E R C IS E
I9.2
Plant Primary Growth and Development
Materials
preparedslidesof Coleusstem (long section)
compound microscope
Introduction
Plantsproduce new cells throughout their llfetime asa result of cell divisions
in meristems.Tissuesproduced from apicalmeris[emsare calledprimary
tissues, and this growth is called primary growth. Primary growth occurs
along the plant axis at the shoot and the root tip. Certain meristem ce11s
divide in such a way that one cell product becomesa new body cell and the
other remainsin the meristem.Beyondthe zone of activecell divrsion,new
cellsbecomeenlargedand specializedfor specificfunctions (resulting,for
example,in vessels,parenchl.rna,and epidermis).The investigationof the
geneticand biochemicalbasisof this ceil differentiationcontinuesto be an
arcaof exciting biologicalresearch.
In this exercise,you will examinea longitudinal sectionthrough the tip of
the stem,observrngthe youngesttissuesand meristemsat the apex,[hen moving down the stem,where you will observemore ma[ure cellsand tissues.
Procedure
1. Examinea preparedsiide of a longitudinal sectionthrough a terminal
bud of Coleus.Use low power to get an overview of the slide; then
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Plant Anatom
increasemagnification.Locatethe apical meristem, a dome of tissue
nestledbetweenthe leaf primordia, young developingleaves.Locate
bud primordia betweenthe leaf and the stem.
the axi11ary
2. Move the specimenunder the microscopeso that cellsmay be viewed
at varying distancesfrom the apex.The youngestcells are at the apex
of rhe bud, and cells of increasingmaturity and differentiationcan be
seenasyou move awayfrom the apex.Follow the earlydevelopmentof
vasculairissue,which differentiatesin relation to the developmenlof primordial leaves.
a. Locatethe narrow,dark tracks of undifferentiated vascular tissue
in the leaf primordia.
b. Observechangesin cell stze and stlucture of the vascularsystemas
you move away from the apex and end with a distinguishablevessel
Ll"-"trt of the xylem, with i.tsspiral cell wall thickening in the older
leaf primordia and stem.You may need [o use the highestpower on
walls.
the microscopeto locatethesespiral ce11
Results
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1. LabelFigure19.2,indicatingthe structuresvisiblein the young stemtip.
2. Modify the figure or sketchdetailsrn the margin of the 1abmanual for
future reference.
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Discussion
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1. Describethe changesin cell sizeand stlucture in the stem tip. Beginat
the youngestcellsat the apex and continue to the xylem cells.
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2. The meristemsof plants continueto grow throughouttheir lifetime,an
exampleof indeterminate growth. lmagine a 2})-year-old oak tree,
with ictive meristemproducingnew buds, leaves,and stemseachyear.
Contrastthis with the growth pattern in humans.
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19.3
Cell Structure of PrimarY Tissues
A11herbaceous (nonwoody) flowering plants produce a completeplant
body composedof primary tissue,derived from apicalprimary merlstem.
This plant body consistsof organs-roots,stems,leaves,flowers,fruits, and
seeds-and tisiuesystem.s-dermal (epidermis),ground (parench;-rna),and
vascular (xyiem and phloem). In this exercise,you will investigatethe cellular structure and orgarizationof plant organsand iissuesby examiningmicroscopicslides.You will make your own thin crosssectionsof stems,and view
preparedslidesof stems,roots,and leaves.Woody stemswill be examj.ned
in Exercise19.4.
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Lab Topic 19: PlantAnatomy
Figure 19.2.
Coleusstem tip. (a) Diagram of entire plant body (b) Photomlcrographof a
longitudinal sectionthrough the terminal bud. (c) Line diagramof the growing
shoot tip with primordial leavessurroundingthe activelydivrdrngapicalmeristem. The most immature cel1sare at rhe tip of the shoot and increasein stages
of deveiopmentand differentiationfarther down the stem. Labelthe cellsand
structuresdescribedin Exercise19.2.
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Plant Anatom
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Lab Study A. Stems
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Materials
preparedslide of herbaceousdicot
stem
dropper bottle of distilled water
small petri dish with 50oloethanol
dropper bottle of 50ologlYcerine
dropper bottle of 0.2% toluidine
blue stain
nut-and-bolt microtome
warm paraffin
living plant for sections
new single-edgedrazor blade
forceps
microscopeslides
coverslips
compound microscope
dissectingneedles
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Introduction
A stem is usually the main stalk, or axis, of a plant and is the only olgan that
producesbuds and leaves.Stemssuppolt leavesand conduct water and
inorsanic substancesfrom the loot to the leavesand carbohydrateproducts
from the leavesto the roots. Most herbaceousstemsare
of photosyrrthesis
ableto phttoslnthesize. Stemsexhlbit severalinterestingadaptations,including waierctoiug" in cacri, carbohydratestoragein some food plants, and
thorns that reduce herbivory in a variety of plants'
you will view a preparedslide of a crosssectionof a stem, and, working
with another student, you will use a simple miclotome-an instrument
used for cutting thin sectionsfor microscopicstudy-to,make your own
slides.You will embed the stem tissuein paraffin and cut thin sections'You
will stain your sectionswith toluidine blue, which will help you distinguish
differentcell types.This simpieprocedureis analogousto the processused
to make preparedslidesfor subsequentlab studies'
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Readthrough the procedureand set up the materials
before beginning.
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Procedure
1. Embed the sectionso[ the stem.
razorblade,cuta 0.5 cm sectiono[a young
a. Usinga new single-edged
bean stem.
b. Obtain a nut-and-boltmicrotome.The nut shouldbe screwedjust inlo
the first threads of the boh. Using forceps, carefully hold the bean
stem upright inside the nut.
c. Pour the warm paraffin into the nut until full. Continue to hold the
top of the stem Lntil the paraffin begins to harden. while the paraffin completely hardens,continue the exerciseby examlning the prepared slide of the stem.
2. Examine a preparedslide of a crosssection through the herbaceous
dicot stem (Color Plate58).
3. ldentify the dermal tissue system, characletizedby a protective cell
laye, covering the plant. lt is composedof the epidermis and the
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you may alsoobservemulticellulartrichomes on
cuticle. Occasionally,
the outer surfaceof the Plants.
4. Locatethe ground tissue system, backgroundtissuethat fills the spaces
betweenepldermlsand vasculartissue.identily the cortex region located
betweentire vascularbundiesand the epidermrs.lt is composedmostly
of parenchyma, but the ou[er part may contain collenchyma
aswell.
Next find the pith region, which occupies[he centerof the stem,inside
rhe ring of vaicular bundles,it is composedof parenchyma.In herba..or,, ,i"-r, thesecel1sprovide support through turgor pressure.This
regionis alsoimportantin storage.
Now ldentify the vascular system, a continuoussystemof xylem and
phloemprovidingtranspoltand support.In your stemsand in many stems,
ihe vasiular bundles (clustersof xylem and phloem) occur in rings
that surround the pith; however,in some groups of flowering plants,
the vasculartissueis arrangedin a complex network'
Observethat eachbundle consistsof phloem tissuetoward the outside
and xylem tissuetoward the inside. A narrow layer of vascularcamstems,is situatedbelween
bium, which may becomeactivein herbaceous
following informatj.onas
the
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note
Take
phloem.
rhe
rhe xylem and
you make your observa[ions.
types:
Phloem tissue is composedof three ce11
a. Dead, fibrous, thick-walled sclerenchyma cells that provide support for the phloem [issueand appearin a clusteras a bundle cap
b. sieve,tube members, which are 1arge,living, elongatedcel1sthat
lack a nucleus at maturity They becomevertlcally allgned to form
sievetubes,and their cytoplasmis interconnectedthrough sieveplates
located at the ends of the cells.Sreveplatesale not usually seenin
crosssectlons.
c. companion cells, which aresmail,nucleatedparenchl.macel1sconcellsby meansof cytoplasmicstrands
,r".t"d to si.eve-tube
Xylem tissue is made up of two cell types:
a. Tiacheids, which areelongated,thick-walledcellswith closed,tapered
ends.They are deadat functional matudty,and their lumens areinterconnectedthrough pits in the cell walls
that are largein diamb. vessel members, which are cylindrical ce11s
joined end to end,
become
eterand deadat functionalmaturity.They
lose their end walls, and form 1ong,ver[icalvessels'
Vascular cambium is a type of tissuethat is locatedbetweenthe xylem
and rhe phloem and which actively divides to give rise to secondary
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B. Completethe Resultssectionbelow for this slide,then retuln to step 9
to pi"pur. and observe your own handmade sections of s[em
preparations.
9. Cut the stem sectionsin the hardenedparaffin'
a. Support the nut-and-bolt microtomewith the bolt head down and,
using the razor blade, carefullyslice off any excessparaflin extendins ;tove the nut. Be carefulto siice1n a direction away from your
boidyand to keep your fingersawayfrom the edgeof the razorblade
(FigureI9.3).
Figure 19.3.
Using the nut-and-bolt microtome.
A pieceof stem is embeddedin paraffin in the bolt As you twist the bolt
up, slicethin sectionsto be stained
and viewed.Slidethe entire blade
through the paraffin to smoothly slice
thin sections.Follow the directionsin
Exercise19.3, Lab StudyA carefully
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Plant Anatom
Be carefulto keepfingersand knucklesaway from the razor
blade.Follow directionscarefully.
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b. Turn the bolt jusf alittle,to extendthe stem/paraffinabovethe edge
of the nut.
c. Producea thin sectionby sllcing off the extensionusing the ful1length
of rhe razor blade,beginning ar one end of the blade and slicing to
the otherend of the blade(seeFigure19.3).
d. Transfereachsectionto a small petri dish containing50% ethanol.
e. Continueto producethin sectionsof stemin this manner.The thinnest
slicesmay curl, but this ls all right if the stemsec[ionremainsin the
paraffin u. you make the rransfer.Cel1types are easierto identify in
very thin sectionsor in the thin edgesof thicker sections'
10. Stainthe sections.
a. Leaverhe sectionsin 50% ethanol rn the petri dish for 5 minutes.
The alcohol/r-res,or preseryes,the tissue.Using dissectingneedlesand
forceps,.urlfu,lly separatethe rissuefrom the surroundingparaffin.
b. Using forceps,move the stem sections,free of the paraffin, to a
cleanslide.
c. Add severaldrops of toluidine blueto coverthe sections.Allow the
sectionsto stainfor 10 to 15 seconds.
d. carefully draw off the stainby placing a pieceof paper towel at the
edgeof the stain.
e. Rinserhe sectionsby adding severaldrops of distilledwater to cover
the sectlons.Draw off the excesswater with a papel towel. Repeatthis
stepuntil the rinse water no longer looks blue.
f. Add a drop of 50ologlycerinero the sectionsand covel them with a
coverslip,being carefulnot to trap bubblesin the preparatron'
Surveythe
g. observeyour secrionsusinga compoundmicroscope.
with
speclmens
the
selecting
powel,
intermediate
1ow
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specone
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the clearestcell struc[ure.
imen to seeall structures.
I1. Fol1owsteps3-7 aboveand identify all sn-uctulesand cells.Incorpolaie
your observationsinto the Resultssection(4, following).
Results
1. Labelthe stem sectionrn Figure 19.4b and c.
7. Were any epidermaltrichomespresenti-nyour stem?
3. Note any featuresnot describedin the procedure.Sketchthesein the
margin of your lab manual for future reference.Return to Procedure
srep9 in this lab study and completethe prepalationof hand secti.ons
of the bean stem.
4. Compareyour hand secrionswith the preparedslide.Modify Figure I9.4
or sketchyour hand sectionin the margin.ls thereany evidenceof vascular cambium and secondarygrowrh (Exercise19.4)?compare your
resultswith thoseof other students.
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Figure 19.4.
Stem anatomy. (a) Diagram of whole plant. (b) Photomicrographof crosssecrion
through the stem portion of the plant. (c) Enlargementof one vascularbundie as
seenin crosssectionof the stem.
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The functionsof cellswere describedin the Summary of
BasicPlantTissuesand CellTypes,which appearednearthe
beginningof this lab topic.
Discussion
1. Which arelargerandmoredlstinct,xylemcelisor phloemcells?
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Plant Anat
2. Whar typesof cellsprovide suppoil of the stem?where arethesecells
locatedin the stem?
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structurerelateto their function, which rs support?
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4. What is the function of xylem?Of phloem?
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Relateparenchymacell functronsto their
many functionsof thesece11s.
observedstructure.
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and your hand sectior-rtiWhut factorsmight be responsiblefor these
differences?
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Lab Study B. Roots
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Materials
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root (crosssection)
preparedslideof buttercup(Ranunculus)
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coloredpencrls
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Introduction
Rootsand stemsoften appearto be similar, exceptthat roots grow in the soil
and stemsabovethe ground. However,somestems(rhizomes)grow underground, and someroots (adventitiousroots) grow aboveground.Rootsand
stemsmay superficially appearsimilar, but they differ significanrly in their
functions.
What are the primary functions of stems?
Rootshave four primary functions:
| . anchorageof the plant in the soil
2. absorptionof water and mineralsfrom the soil
3. conduction of water and mineralsfrom the regronof absorptlonto the
baseof the stem
4. starchstorageto varying degrees,dependingon the plant
Hypothesis
our working hypothesisfor this investigationis that the structureof the
plant body is relatedto particularfunctions.
Prediction
Basedon our h;,pothesis,make a predictronabout rhe similarityof root and
stem structuresthat you expectto observe(iilthen).
You will now test your hypothesisand predicrionsby observingrhe external structureof roots and their internal cellularstruclureand orsanization
in a preparedcrosssection.This activityis an exampleof cotlectingevidencefrom observationsrather than conductinga controlledexperiment.
Procedure
1. Examinethe externalroot slructure.When a seedgerminates,it sends
down a primary root, or radicle, into the soil. This root sendsout side
branchescalledlateralroots, and thesein turn branch out until a root
e\/ctPm
i c fnrmer]
If the primary root continuesto be the largestand most important part
of the root system,the plant is said to have a taproot system.If many
main roots are forrned, the plant has a fibrous root system.Most grasses
havea fibrous root system,as do treeswith roots occurringwithin 1 m
of the soll surface.Carrots,dandelions,and pine treesare examplesof
plants having taproots.
a. Observeexamplesof fibrousrootsand laprootson demonstration
in
the laborator;r
b. Sketchthe two types of roots in the margin of your lab manual.
7
Plant Anat
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Cross section of the buttercup root. (a) Whole plant. (b) Photomicrographof a
crosssectionof a root. (c) Eniargementof the I'ascuLatcylinder.Labelthe root
basedon your obsen'ationsof a preparedmicroscopeslide.
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Plant Anatom
2. Examinethe internal root structure.
a. srudy a slide of a crosssectionthrough a buttercup (Ranunculus)root.
Note that the root lacksa centralpith. The ,rascula.tissueis located
in the cenrerof the roor and is calledihe vascular cylinder (Frgure19.5b).
b. Look for a cortex.The cortex is primarilycomposedof largeparenchyna
cellsfilled wirh numerouspurple-stainedorginelles.which of the iour
functions of roots listed in rhe introduction ro this lab study do you
think is relatedto thesecorticaIcellsand their orsanelles?
c. Identify the following tissuesand regionsand 1abe1
Figure I9.5b
and c accordingly:epidermis, parench).nna
of cortex, vasi=ularcylinder, xylem, phloem, endodermis, and pericycle. The endodermis
and the pericycleare unique to roots. The endodermlsis the innermost cell layerof the cortex.The walls of endoderrnalcellshavea band
calledthe Casparianstrip-made of suberin,a wary materiai-thar
extendscompletelyaround eachcell, as shown in Fisure 19.6. This
strip formsa barrierto rhepassage
ol anythingmovingbetweenadjacent cellsof the endodemis. AII warerand dissolvedmalerialsabsorbed
by the epldermalroot hairs and transportedinward through the
co_rtexmusr first passthrough rhe living cyroplasmof endoJermal
cells,beforeenterlngthe vasculartissues.The pericycleis a layer of
dividing cellsimmediatelyinside rhe endodermis;iigives rise io lateral roo[s.
Figure 19.6.
Root endodermis. The endodermisis
composedof ce1lssurroundedby a
band containingsuberin,calledthe
Caspanansfrip (seenin enlargement),
that preventsthe movementof materials along the ce11s'walls
and intercellular spacesinto the vascularcyiinder.
Materialsmust crossthe cell membranebeforeenteringthe vascular
tl S S U e.
d
6t
Results
in Figure 19'6'
1. ReviewFigure 19.5 and note comparablestructures
T.Usingacoloredpencil,highlighttherepresenlationsofs[ ructulesor
cellsToundin the root but not seenin the stem'
Discussion
l.Suggesttheadvantageoftaprootsandoffibrousrootsunderdifferent
environmental conditions'
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predictions(p' 5I3)?
Did your observationssuppoft your hypothesisand
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roots and stems'How do
Comparethe structure and organizationof
thesetwo org,ansdiffer?
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4. Expiain the relationship of structure and function
cells found onlY in roots'
ior two structuresor
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cuticle' Can you explain why
5. Note that the epidermis of the root lacks a
this might be advantageous?
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is the endodermisimpor6. What is the function of the endodermis?Why
Lantto the successof plants in the land enr"rronment?
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Lab Topic 19: PlantAnarom
Lab Study C. Leaves
Materials
prepared slide of Illac (Synngla)leaf dropper bottlesof warer
slides
leavesof purple heart (Setcreasia)
compound microscope
kept in saiineand DI warer
coverslips
Introduction
Leavesareorgansespeciallyadaptedfor photosFrthesis.
The thin bladepor,
tionprovides,a very large surface arealor the'absorprionof lighr
andrhe
uptake of carbon dioxide rhrorrghsromara.The leaf is basicall"y
arayerof
parenchymacells (the mesophyll) berweenrwo layersof epidermis.
The
loosearrangementof parenc6ymacellswithin the reafarlows
for an exrensivesurfaceareafor the rapid exchangeof gases.specializedepidermal
cells
calledguard cells allow the exchangeof gises und .,ruporution
of warer at
the leaf surface.Guard cells are photosynrhetic(unrike other
epidermal
cells),and are capableof changingshapein responseto compiex
environmenlal and physiologicalfactors.currenr reseaichindicatestirat
the open_
ing of the stomatais the,resultofthe-activeuptakeof K- and ,rbr.qr.rrt
changes
in turgor pressurein the guard cells.
In thrs-labstudy,you wiil examinethe structureof a leaf in
crosssection.
You will observesromaraon the leaf epidermrsand will study
the actrvity
of guard ceilsunder differentconditions.
Procedure
1' Beforebeginning your observationsof the leaf crosssection,
compare
the shapeof the leaf on your slide wirh Figure 19.7a andb on
the next
page.
2. Observethe internal leaf structure.
a. Examinea crosssectionthrough a li1acleaf and identify rhe
folrowing cells or structures:cuticle, epidermis (upper and
1ower),
parenchl'rnawith chloroplasts(mesophyll), .,,our..rlu.
bundre with
phl:"-* and xylem, and stomata wlih guard cells and substom,
atal chamber.
b. The vascularbundles of the leaf are ofren cailedveins and
can be
seenin both crosssectlonand longitudinalsectionsof the leaf.
observe
the structureof cellsin the centralmidvein. Is xylem or phroem
on
top in the leaf?
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Plant Anatom
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Figure 19.7.
Leaf structure. (a) Whole plant (b) Photomicrographof a leaf crosssection
through the midvein. (c) Photomicrographof a leaf crosssectionadjacentto the
midvein.
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Lab Topic 19: PlantAnatomy
5I9
c. Observethe distribution of stomatain the upper and lower epidermis. Where are they more abundant?
d. Label the crosssectionof the leaf in Figure 19.7.
3. Observethe leaf epidermisand stomata.
leaves,one placed in saline fbr an hour and
a. Obtain two Setcreasia
the other placedin distilled water for an hour.
b. Label two microscopeslides,one "saline"and the other "HrO."
c. To removea small pieceof the lower epidermis,fold the leaf in half,
with the lower epidermisto the inside.Tearthe leaf,pulling one end
toward the other, stripping off the iower epidermis(Figure 19.8). If
you do this correctlyyou will seea thin purple layerof lower epidennis
at the torn edgeof the leaf.
d. Removea smail section of the epidermis from the leaf in DI water
and moun[ lt in water on the appropriateslide, being sure that the
outsidesurfaceof the leafis facingup. View the slideat low and high
power on your microscope,and observethe structureof the stomata. Sketchyour observationsin the margin of your lab manual.
e. Removea sec[ionof the enidermisfrom the leaf in salineand mount
it on the appropriate
slidein a drop of the salinc.Makesurerharthe
outsidesurfaceof the leafis facingup. View the slidewith low power
on your microscope,and observethe structureof the stomata.Sketch
your observationsin the margin of your lab manual.
Results
1. Reviewthe leafcrosssectionin Figure19.7.
2. Describethe structureof the stomataon leaveskent in DI water.
3.
Describe the structure of the stomata on leaves kept in saline
Discussion
1.
Describe the functions of leaves.
Provide evidencefrom your observationsof leaf structure to support
the hypothesisthat structure and function are related.Be specificin
your examples.
Peeled
lower
epidermis
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Figure 19.8.
Preparation of leaf epidermis peel.
Bend the leaf in half and peel away
the lower epidermis.Removea small
sectionof lower epidermisand make
a wet mount.
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Lab T opic l 9 : Pl a n tAn a to my
3. Explain the observationthat more stomataarefound on the lower surlaceoi the leafthan on the upper.
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4. Explain the differencesobserved,if any,betweenthe stomatafrom leaves
kept in DI water and those kept in saline.Utilize your knowledgeof
osmosisto explain the changesin the guard cells. (In this activity,you
stimulatedstomatalclosureby changesin turgor pressuredue to saline
rather than K* transport.)
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E X E RCI S E
1 9 .4
Cell Structure of Tissues
Producedby SecondaryGrowth
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Materials
*
preparedslidesof basswood(Tilia) stem
compound microscope
'r
Introduction
*
Secondarygrowth arisesfrom meristematictissuecalled cambium. Vascular
cambium and cork cambium are two types of cambium. The vascularcambium is a single layer of meristematic cells located between the secondary
phloem and secondaryxylem. Dividing cambium cellsproducea new cell
at one time toward the xylem, at anothertime toward the phloem. Thus, each
cambialcell producesfiles of cells,one toward the inside of the stem,another
toward the outside,resultingin an increasein stem girth (diameter).The secondary phloem cells become differentiated into sclerench).nnafiber cells,
sieve-tubecells,and companion cells.Secondaryxylem cellsbecomedifferentiatedinto tracheidsand vesselelements.Certaincambialcellsproduce
parenchyna ray cellsthat can extendradiaily through the xylem and phloem
of the stem.
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The cork cambium is a type of meristematictissuethat divides, producing
cork tissueto the outsideof the stemand other cellsto the inside.The cork
cambium and the secondarytissuesderived from it are called periderm.
The periderm layer replacesthe epidermisand cortex in stemsand roots
with secondarygrowth. Theselayers are continually broken and sloughed
off as the woody plant grows and expandsin diameter.
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Lab Topic 19: Plant Anatomy
Procedure
l.
Examinea crosssectionof a woody stem (Color Piate59).
a. Observethe cork cambium and periderm in the outer layersof the
stem.The ouier cork cellsof the periderm havethick walls impregnatedwith awa^J materialcalledsuberin. Thesecellsaredeadat maturity. The thin layer of cells that may be visible next to the cork cells
is the cork cambium. The periderm includesthe layersof cork and
associated
cork cambium.The term bark is usedto describethe neriderm and phloem on the outsideof woody plants.
b. Observethe cellularnature of the listed tissuesor structures,beginning at the perlderm and moving inward to the centralpith region.
Sclerenchyma fibers have thick, dark-stained cell walls and are
locatedin bands in the phloem. Secondaryphloem cellswith thin
cell walls alternaiewith the rows of fibers.The vascular cambium
appearsas a thin line of small, activelydividing cellslying between
the outer phloem tissueand the extensivesecondary
Secondary
"y1.-.
xylem consistsof distinctiveopen cells that extend in layersto the
central pith region. Lines of parench).'rnacells one or two cells thick
form lateral rays that radiate from the pith through the xylem and
expand to a wedge shapein the phloem, forming a phloem ray.
2. Note the annual rings of xylem, which make up the wood of the stem
surrounding the pith. Each annual ring of xylem has severalrows of
early wood, thin-walled, large-diametercells that grew in the spring
and, outsrdeof these,a few rows of late wood, thick-walied,smallerdiameter cells that grew in the summer.
3. By counting the annuairings of xylem, determinethe ageof your stem.
Note that the phloem regionis not involvedwith determiningthe age
of the tree.
Results
I.
ReviewFigure 19.9 on the next pageand Color Plate59.
2. Sketchin the margin of your lab manual any detailsnot representedin
the figure that you might need for future reference.
3. lndicate on your diagram the region where primary tissuescan still
be found.
Discussion
1. Whathashappenedto theseveralyears
of phloemtissueproduction?
Basedon your observationsof the woody stem,doesxlrlem or phloem
providestructuralsupportfor trees?
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LabT opi c l q : Pl a n tAn a to my
Cork
C o r kc a m b i um
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Phloemray
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Phloem
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V a s c u l a cr a mb i u m
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Xylemvessel
Lateralray
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Pith
f.'", " '
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C o r kc a m b i u m
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c.
Vascularcambium
Xylemvessel
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P i th
,lLrilqi
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Annuairing
Periderm
c.
Figure 19.9.
Secondary growth. (a) Whole woody p1ant.(b) Photomicrographof a cross
sectionof a woody stem. (c) Comparethe correspondingdiagramwith your
modrfy the diagramto correspond
observationsof a preparedslide. If necessar)-.
to your speclmen.
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Lab Topic 19: Plant Anatomy
3. What function might the ray parenchymacel1sserve?
4.
How might [he structure of early wood and iate wood be related to seasonal conditions and the function of the cells? Think about environmental conditions during the growing season.
E X E R C IS E
I9.5
Grocery StoreBotany:
Modifications of Plant Organs
Materials
v ar iet y oI p ro d u c e : s q u a s h .l e ttu c e .c e l e ry.carrot. w hi te potato, sw eet
potato, asparagus, onion, broccoli, attd any other produce you w"rsh
to examlne
Introduction
Every day you come into contactwith the plant wor1d,particularlyin the
selection,preparation,and enjoymento[ food. Most agriculturalfood plants
haveundergoneextremeselectionfor specificfeatures.For example,broccoli, cauliflower,cabbage,and brusselssproutsareall membersof the same
speciesthat haveundergoneselectionfor differentfea[ures.In this exercise,
you will apply your botanicalknowledgeto the laboratoryof the grocerystore.
Procedure
1. Working wrth anotherstudent, examinethe numerousexamplesof roo[,
stem, and leaf modifications on demonstration.(There may be some
reproductives[ructuresaswell. Referto Lab Topic 16, PlantDiversityII,
if needed.)
2. For eachgroceryitem, determinethe type of plant organ,its modificatron,and its prlmary function.How will you decidewhat is a root, stem,
or leaf?Reviewthe characteristicsof theseplant organsand examine
your producecarefuLly.
Results
CompleteTable19.I on the next page.
523
Lab Topic 19: Plant Anatomy
Questions for Review
Use Table 19.2 to describethe structureand function of the cell tlpes
seenin lab today. Indicate the location of thesein the various plant
organsexamined.
Some tissuesare composedof only one type of cell; others are more
complex. List the cel1types observedin xyiem and in phloem.
Xylem:
Phloem:
What characteristicof sieve-tubestructurepror'rdesa clue to the role of
companioncells?
4. Compareprimary and secondarygrowth. What ceils divide to form primary tissue?To form secondarytissue?Can a plant haveboth primary
growth and secondarygrowth?Explain,providing evidenceto support
your answer.
Applying Your Knowledge
1. Cells of the epidermis frequently retain a capabillty for cell division
Why is this important? (Hint: What is their function?)
2.
Why is the endodermis essential in the root but not in the stem?
525
Questions for Review
1. Use Table I9.2 to describethe structureand function of the cell types
seenin lab today Indicate the location of thesein the various plant
organsexamined.
2. Sometissuesare composedof only one tlpe of cell; others are more
compiex. List the cell types observedin xylem and in phloem'
Xylem:
Phloem:
What characteristicof sieve-tubestructure provides a clue to the role of
companion cells?
4. Compareprimary and secondarygrowth. What cells divide to form pnmary tissue?To form secondarytissue?Can a plant have both primary
growth and secondarygrowth? Expiain, providing evidenceto support
your answer.
Applying Your Knowledge
1. Cells of the epidermis frequently retain a capability for ceil division.
Whv is this importanL?(Hint: What is their function?)
2. Why is the endodermisessentialin the root but not in the stem?
526
,d
Lab Topic 19: Plant Anatomy
Table 19.2
Structureand Function of Plant Cells
Cell Type
Epidermis
Structure
'rF
Function
Plant Organ
+
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*
Parenchyma
*
Collenchyma
*
*
Sclerench)..rna
*
Tiacheids
FF
Fr
Vessels
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Fr
Sievetubes
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Endodermis
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Pri m errz
meristems
Vascular
cambium
Guard ce1ls
Periderm
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Ruy
parenchl-rna
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PlantAna
3. When laterai roots grow outward from the pericycle,what effectdoes
this have on the cortex and the epidermis?(Hinr: Reviewthe structure
of the root and the location of thesetissues.)
4. In the summerof I998, afterextremelyhot. dry wearher.
the Ceorgia
corn harvestwas expectedto be reducedby at least25olo.Uslng your
knowledgeof the dual functions of guard cellsrelative[o water rerention and gas exchange,explain the reduction in photosynthetic
nroductivitv
5. The belt buckle of a standing2)-year-oid man may be a foor higher
than it waswhen he was 10, but a naii driven into a 10,year-oldtreewill
be at the sameheighr I0 yearslater.Explain.
6. Expiain, from a ce11ular
point of r,rew,how it is possibleto determrne
the ageof a tree.
7. The oldestliving organismson Earth areplants.Somebristleconepines
are over 4,000 years old, and a desertcreosotebush is known to be
10,000yearsold. What specialfeatureof plantspror,rdesfor this incredible longevity?How do plants differ from animalsin their parrern of
growth and development?
Plant ce1lshave ce1lwalls and animal cells do nor. How does this diflerence
relate to drfferences in plant and animal function?
tr
528
f,
Lab Topic 19: Plant Anatomy
Table 19.3
Adaptationsof Plant Cellsand Structuresto the Land Environment
Environmental
Factor
Adaptations
to Land Environment
Desiccation
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Tiansportof materials
betweenplant and
environment
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;
Gas exchange
-4.
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Anchorage in substrate
;
Tiansportof materials
within piant body
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sStructuralsupport 1n
responseto gravity
Sexualreproduction
without water
Dispersalof offspring
from immobile parent
9. Many of the structural featuresstudied in this laboratory evolvedin
ol the terrest
rial habitat.
resDonse
lo lhe environmentalchallenpes
CompleteTable19.3 on this page,naming the cells,tissues.and organs
that have allowed vascularplants to adapt to each environmental
factor.
Investigative Extensions
;
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1.
The nut-and-bolt microtome can be used to separatea section of almost
ar''y pafi of a p1ant.You might grow your own plants from seedsand then
embed small sections of each plant organ in paraffin and prepare slides
for observation. Visualize the orientation of your material and sections
before embedding.
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