Download pdf - Unit 2 Module 2A The Cellular Basis of Life Basic Cell ...Basic Cell Structure and Function Cells are the basic units of life. Therefore, an understanding of cells is essential for

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Unit 2Unit 2The Cellular Basis of LifeThe Cellular Basis of Life

2A. Basic Cell Structure and Function2A. Basic Cell Structure and Function2B. Viruses2B. Viruses2C Membranes and Cell Transport2C Membranes and Cell Transport

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2C. Membranes and Cell Transport2C. Membranes and Cell Transport2D. Energy and Metabolism 2D. Energy and Metabolism 2E. How Cells Harvest Energy2E. How Cells Harvest Energy2F. Photosynthesis2F. Photosynthesis2G. Cell Communication2G. Cell Communication

Module 2A Module 2A Basic Cell Structure and FunctionBasic Cell Structure and Function

Cells are the basic units of life. Cells are the basic units of life. Therefore, an understanding of cells is Therefore, an understanding of cells is essential for an understanding of living essential for an understanding of living

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g gg gorganisms.organisms.In this module, we will take an In this module, we will take an introductory look at the structure and introductory look at the structure and function of living cells.function of living cells.

Objective # 1Objective # 1

Describe the general plan Describe the general plan of cellular organization of cellular organization

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common to all cells.common to all cells.

Objective 1Objective 1

In 1655, the English scientistIn 1655, the English scientist Robert Robert HookeHooke coined the term “cellulae” for coined the term “cellulae” for the small boxthe small box--like structures he saw like structures he saw while examining a thin slice of cork while examining a thin slice of cork

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under a microscope.under a microscope.A few years later, a Dutchman named A few years later, a Dutchman named Anton van LeeuwenhoekAnton van Leeuwenhoek observed observed and described numerous living cells.and described numerous living cells.

Onion CellsOnion Cells

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Further study has shown that all cells Further study has shown that all cells have the following basic structure :have the following basic structure :A thin, flexible A thin, flexible plasma membraneplasma membranesurrounds the entire cell.surrounds the entire cell.

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The interior is filled with a semiThe interior is filled with a semi--fluid fluid material called the material called the cytoplasmcytoplasm..Also inside are specialized structures Also inside are specialized structures called called organellesorganelles and the cell’s and the cell’s genetic genetic materialmaterial..

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Plasma membrane

Cytoplasm

O ll

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Organelles

Identify the Basic Components of a cell

Genetic material



List and explain the 3 List and explain the 3 i i l f h ll hi i l f h ll h

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principles of the cell theory.principles of the cell theory.


In 1838 In 1838 –– 1839, the German scientists 1839, the German scientists SchleidenSchleiden and and SchwannSchwann, proposed the , proposed the first 2 principles of the cell theory:first 2 principles of the cell theory:

All organisms are composed of one orAll organisms are composed of one or

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All organisms are composed of one or All organisms are composed of one or more cells.more cells.Cells are the basic units of life.Cells are the basic units of life.


About 15 years later, the German About 15 years later, the German physician physician Rudolf VirchowRudolf Virchow proposed proposed the third and final principle of the cell the third and final principle of the cell theory:theory:

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All cells arise from preAll cells arise from pre--existing cells.existing cells.

This is now qualified with “under the This is now qualified with “under the current conditions on earth”.current conditions on earth”.


Describe some factors that Describe some factors that act to limit cell sizeact to limit cell size

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act to limit cell size.act to limit cell size.


Why are cells so small?Why are cells so small?Because a cell usually has only 1 or 2 Because a cell usually has only 1 or 2 sets of genetic instructions, there is a sets of genetic instructions, there is a limit to the volume of cytoplasm that limit to the volume of cytoplasm that can be effectively controlledcan be effectively controlled

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can be effectively controlled.can be effectively controlled.Methods used to transport materials Methods used to transport materials and information inside the cell are and information inside the cell are efficient over short distances only.efficient over short distances only.Problem with surfaceProblem with surface--toto--volume ratio.volume ratio.

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Objective 3Objective 3Assuming constant shape, as an object Assuming constant shape, as an object gets bigger what happens to its surface gets bigger what happens to its surface area?area?What happens to its volume?What happens to its volume?

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What happens to its surfaceWhat happens to its surface--toto--volume volume ratio?ratio?The S/V ratio decreases because The S/V ratio decreases because volume increases at a faster rate than volume increases at a faster rate than surface area.surface area.

The ratio of Surface Area to Volume gets smaller as this cell

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Cell radius (r)

Surface area (4πr2)

Volume ( πr3)

1 unit

12.57 unit2

4.189 unit3

10 unit

1257 unit2

4189 unit3

Surface Area- /Volume 3 0.3


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as this cell gets larger


Why is decreasing S/V ratio a problem?Why is decreasing S/V ratio a problem?In order to survive , a cell must exchange In order to survive , a cell must exchange materials with its environment. Cell materials with its environment. Cell volume determines the amount of volume determines the amount of

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materials that must be exchanged, while materials that must be exchanged, while surface area limits how fast exchange can surface area limits how fast exchange can occur. In other words, as cells get larger occur. In other words, as cells get larger the need for materials increases faster the need for materials increases faster than the ability to absorb them.than the ability to absorb them.


How have organisms become larger in How have organisms become larger in spite of these problems?spite of these problems?

At first, single cells simply got larger. At first, single cells simply got larger.

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g p g gg p g gAverage eukaryotic cell is 1,000 X Average eukaryotic cell is 1,000 X larger in volume than average larger in volume than average prokaryotic cell. Eventually, limits to prokaryotic cell. Eventually, limits to size of individual cells were reached.size of individual cells were reached.


CoenocyticCoenocytic organisms organisms –– sac of sac of cytoplasm continued to increase in size cytoplasm continued to increase in size but became multinucleate and evolvedbut became multinucleate and evolved

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but became multinucleate and evolved but became multinucleate and evolved thin, flat shapes or long, narrow shapes thin, flat shapes or long, narrow shapes to increase S/V ratio. e.g. some to increase S/V ratio. e.g. some protists, fungiprotists, fungi


ColonialColonial organisms organisms –– instead of one instead of one large mass of cytoplasm, body was large mass of cytoplasm, body was divided into many small, similar cells, divided into many small, similar cells, each with its own nucleus. e.g. some each with its own nucleus. e.g. some

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protistsprotistsMulticellularMulticellular organisms organisms –– similar to similar to colonial except cells became colonial except cells became specialized to carry out specific specialized to carry out specific functions. e.g. plants, animalsfunctions. e.g. plants, animals

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Describe the structure of a Describe the structure of a i l k i lli l k i ll

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typical prokaryotic cell.typical prokaryotic cell. Pl b

RibosomesNucleoid (DNA)

Cytoplasm


Be able to describe the structure and function all cell parts shown on


Flagellum

Cell wallPlasma membrane

Capsule

Pili

parts shown on this diagram of a typical prokaryotic cell


Fig. 4.4Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display.

Nucleoid

Cytoplasm

Electron micrograph of a photosynthetic prokaryotic cell

Photosynthetic membranes

Cell wall

Plasmamembrane

0.6 µm

Courtesy of E.H. Newcomb & T.D. Pugh, University of Wisconsin22


Describe the structure of a Describe the structure of a i l k i lli l k i ll

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typical eukaryotic cell.typical eukaryotic cell.

Nucleus

NucleolusNuclear pore

Ribosomes

Ribosomes

Cytoskeleton

Intermediatefilament

MicrotubuleActin filament

C t i l

Smooth endoplasmic reticulumRough endoplasmic reticulum

Microvilli

Nuclear envelope

CytoplasmLysosome

Centriole

Plasma membraneMitochondrion

Golgi apparatus

ExocytosisVesicle

Peroxisome


Be able to describe the structure and function of all cell parts shown on this diagram of a typical animal cell

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Nucleus

NucleolusNuclear pore

Intermediate filament

Ribosome

Cytoplasm

CytoskeletonIntermediatefilamentMicrotubuleActin filament(microfilament)

MitochondrionGolgiapparatus

Peroxisome

Smooth endoplasmic reticulumRough endoplasmic reticulum

Nuclear envelope

Central vacuole


y p

Plasma membrane

Vesicle

Plasmodesmata

Adjacent cellwall Cell wall

Chloroplast


Be able to describe the structure and function of all cell parts shown on this diagram of a typical plant cell

NucleusNucleus

Repository of the genetic informationRepository of the genetic informationMost eukaryotic cells possess a single nucleusMost eukaryotic cells possess a single nucleusNucleolus Nucleolus –– region where ribosomal RNA synthesis region where ribosomal RNA synthesis takes placetakes placeNuclear envelopeNuclear envelope

bb

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2 phospholipid bilayers2 phospholipid bilayersNuclear pores Nuclear pores –– control passage in and outcontrol passage in and out

In eukaryotes, the DNA is divided into multiple linear In eukaryotes, the DNA is divided into multiple linear chromosomeschromosomes

Chromatin is chromosomes plus proteinChromatin is chromosomes plus protein

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Be able to describe the structure and function of the eukaryotic nucleus

RibosomesRibosomes

Cell’s protein synthesis machineryCell’s protein synthesis machineryFound in all cell types in all 3 domainsFound in all cell types in all 3 domainsRibosomal RNA (rRNA)Ribosomal RNA (rRNA)--protein protein complexcomplexco p eco p eProtein synthesis also requires Protein synthesis also requires messenger RNA (mRNA) and transfer messenger RNA (mRNA) and transfer RNA (tRNA)RNA (tRNA)Ribosomes may be free in cytoplasm Ribosomes may be free in cytoplasm or associated with internal membranesor associated with internal membranes28

Fig. 4.9

Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display.

Large subunit

Small subunit

Ribosome

Be able to describe the structure and function of ribosomes

EndomembraneEndomembrane SystemSystem

A system of membranes that run through A system of membranes that run through the cytoplasm and divide the cell into the cytoplasm and divide the cell into compartments where different cellular compartments where different cellular functions occurfunctions occurPresent in e kar otic cells onlPresent in e kar otic cells onl

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Present in eukaryotic cells onlyPresent in eukaryotic cells onlyComponents of the Components of the endomembraneendomembrane system system include: the endoplasmic reticulum, the include: the endoplasmic reticulum, the Golgi, Golgi, lysosomeslysosomes, , microbodiesmicrobodies, vacuoles, , vacuoles, and vesiclesand vesicles

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Endoplasmic reticulumEndoplasmic reticulum

Rough endoplasmic reticulum (RER)Rough endoplasmic reticulum (RER)Attachment of ribosomes to the membrane gives a Attachment of ribosomes to the membrane gives a rough appearancerough appearanceSynthesis of proteins to be secreted, sent to Synthesis of proteins to be secreted, sent to lysosomeslysosomes or plasma membraneor plasma membrane

S h d l i i l (SER)S h d l i i l (SER)

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Smooth endoplasmic reticulum (SER)Smooth endoplasmic reticulum (SER)Relatively few bound ribosomesRelatively few bound ribosomesVariety of functions Variety of functions –– synthesis, store Casynthesis, store Ca2+ 2+ , , detoxificationdetoxification

Ratio of RER to SER depends on cell’s functionRatio of RER to SER depends on cell’s function

Be able to describe the structure and function of the rough and smooth endoplasmic reticulum:

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Golgi apparatusGolgi apparatus

Flattened stacks of interconnected Flattened stacks of interconnected membranes (Golgi bodies)membranes (Golgi bodies)Functions in packaging and Functions in packaging and distribution of molecules synthesized distribution of molecules synthesized

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at one location and used at another at one location and used at another within the cell or even outside of itwithin the cell or even outside of itCisCis andand trans trans facesfacesVesicles transport molecules to Vesicles transport molecules to destinationdestination

Be able to describe the structure and function of

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the Golgi apparatus:

LysosomesLysosomes

MembraneMembrane--bound sacs that contain bound sacs that contain digestive enzymesdigestive enzymesArise from the Golgi apparatusArise from the Golgi apparatusEnzymes catalyze the breakdown of Enzymes catalyze the breakdown of E y es cata y e t e b ea dow oE y es cata y e t e b ea dow omacromoleculesmacromoleculesDestroy cells or foreign matter that the Destroy cells or foreign matter that the cell has engulfed by cell has engulfed by phagocytosisphagocytosis

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Microbodies

• Variety of enzyme‐bearing, membrane‐enclosed vesicles

• One type are peroxisomesperoxisomes– Contain enzymes involved in the oxidation of fatty acids

– H2O2 produced as by‐product – rendered harmless by catalase

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VacuolesVacuoles

MembraneMembrane--bounded sacs that carry bounded sacs that carry out various functions depending on out various functions depending on the cell typethe cell type

There are different types of vacuoles:There are different types of vacuoles:

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There are different types of vacuoles:There are different types of vacuoles:Central vacuole in plant cellsCentral vacuole in plant cellsContractile vacuole of some Contractile vacuole of some protistsprotistsStorage vacuolesStorage vacuoles

Electron micrograph showing the large central vacuole of a

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plant cell


1.

Roughendoplasmicreticulum

Membraneprotein

Newlysynthesizedprotein

Vesicle containingproteins buds fromthe rough endo-plasmic reticulum,diffuses through thecell and f ses to Transport

Nucleus

Nuclear poreNuclear poreRibosome

Be able to describe the movement of proteins through the endomembrane

2.

3.

Golgi membrane protein

Cisternae

Secretory vesicle

Cell membrane

Extracellular fluid

cell, and fuses tothe cis face of theGolgi apparatus. Smooth

endoplasmicreticulumcis face

GolgiApparatus

trans face

The proteins aremodified andpackaged intovesicles fortransport. Secreted

protein

The vesicle maytravel to the plasmamembrane,releasing itscontents to theextracellularenvironment.

Transportvesicle

system of a eukaryotic cell:

MitochondriaMitochondria

Found in all types of eukaryotic cellsFound in all types of eukaryotic cellsBound by membranesBound by membranes

Outer membraneOuter membraneIntermembrane spaceIntermembrane spaceInner membrane has cristaeInner membrane has cristaeMatrixMatrix

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MatrixMatrix

On the surface of the inner membrane, and also On the surface of the inner membrane, and also embedded within it, are proteins that carry out embedded within it, are proteins that carry out oxidative metabolismoxidative metabolismHave their own DNAHave their own DNA

Be able to describe the structure and function of a mitochondrium:

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ChloroplastsChloroplasts

Organelles present in cells of plants and Organelles present in cells of plants and some other eukaryotessome other eukaryotesContain chlorophyll for photosynthesisContain chlorophyll for photosynthesisSurrounded by 2 membranesSurrounded by 2 membranes

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yyThylakoidsThylakoids are membranous sacs within are membranous sacs within the inner membranethe inner membrane

GranaGrana are stacks of are stacks of thylakoidsthylakoidsHave their own DNAHave their own DNA

Be able to describe the structure and function of a chloroplast:

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EndosymbiosisEndosymbiosis

This theory proposes that some eukaryotic This theory proposes that some eukaryotic organelles evolved by a symbiosis between organelles evolved by a symbiosis between two cells that were each freetwo cells that were each free--livinglivingOne cell, a prokaryote, was engulfed by One cell, a prokaryote, was engulfed by and became part of a larger cell hich asand became part of a larger cell hich as

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and became part of a larger cell, which was and became part of a larger cell, which was the precursor of modern eukaryotesthe precursor of modern eukaryotesOrganelles that probably arose by Organelles that probably arose by endosymbiosisendosymbiosis include mitochondria and include mitochondria and chloroplastschloroplasts

Some eukaryotic organelles evolved through the

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process of endosymbiosis:

CytoskeletonCytoskeleton

A network of protein fibers and tubes A network of protein fibers and tubes found in all eukaryotic cellsfound in all eukaryotic cells

Supports the shape of the cell Supports the shape of the cell Keeps organelles in fixed locationsKeeps organelles in fixed locations

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Dynamic system Dynamic system –– constantly forming constantly forming and disassemblingand disassembling

3 Components of the Cytoskeleton3 Components of the Cytoskeleton

Microfilaments (Microfilaments (actinactin filaments)filaments)Two protein chains loosely twined togetherTwo protein chains loosely twined togetherMovements like contraction, crawling, “pinching”Movements like contraction, crawling, “pinching”

MicrotubulesMicrotubulesLargest of the Largest of the cytoskeletalcytoskeletal elementselements

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DimersDimers of αof α-- and βand β--tubulintubulin subunitssubunitsFacilitate movement of cell and materials within cellFacilitate movement of cell and materials within cell

Intermediate filamentsIntermediate filamentsBetween the size of Between the size of actinactin filaments and microtubulesfilaments and microtubulesVery stable Very stable –– usually not broken downusually not broken down

9

Be able to describe the structure and function of the 3 components of the cytoskeleton:

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CentrosomeCentrosome

Region containing a pair of Region containing a pair of centriolescentriolesCentriolesCentrioles function as microtubulefunction as microtubule--organizing centers. They can initiate organizing centers. They can initiate the assembly of new microtubules.the assembly of new microtubules.Animal cells and most Animal cells and most protistsprotists have have centriolescentriolesPlants and fungi usually lack Plants and fungi usually lack centriolescentrioles

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A pair of centrioles. Each centriole is composed of 9 triplets of microtubules:

Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display.

Microtubule triplet

Cell MovementCell Movement

Essentially all cell motion is tied to the Essentially all cell motion is tied to the movement of movement of actinactin filaments, filaments, microtubules, or bothmicrotubules, or bothSome cells crawl using Some cells crawl using actinactin

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ggmicrofilamentsmicrofilamentsEukaryotic flagella and cilia have 9 + 2 Eukaryotic flagella and cilia have 9 + 2 arrangement of microtubulesarrangement of microtubules

Not like prokaryotic flagellaNot like prokaryotic flagella

Be able to describe the structure and function of a eukaryotic flagellum. Cilia have a similar structure, except they are shorter and more numerous.

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A green algal cell with numerous flagella and a paramecium covered withcovered with cilia

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Eukaryotic cell wallsEukaryotic cell wallsPlants, fungi, and Plants, fungi, and many many protistsprotistsDifferent from Different from prokaryoteprokaryoteProkaryotes Prokaryotes --yypeptidoglycanpeptidoglycanPlants and Plants and protistsprotists ––cellulosecelluloseFungi Fungi –– chitinchitinPlants Plants –– primary and primary and secondary cell wallssecondary cell walls

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Extracellular matrix (ECM)Extracellular matrix (ECM)

Animal cells lack cell wallsAnimal cells lack cell wallsSecrete an elaborate mixture of Secrete an elaborate mixture of glycoproteinsglycoproteins into the space around into the space around themthem

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Collagen may be abundantCollagen may be abundantForm a protective layer over the cell Form a protective layer over the cell surfacesurfaceIntegrinsIntegrins link ECM to cell’s link ECM to cell’s cytoskeletoncytoskeleton

Extracellular matrix surrounding an animal cell

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Table 4.2Table 4.2

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Describe the similarities and Describe the similarities and differences between differences between prokaryotic and eukaryotic prokaryotic and eukaryotic

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cells.cells.

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ProkaryotesProkaryotes EukaryotesEukaryotesorganismsorganisms monera monera

(bacteria)(bacteria)all other all other organismsorganisms

sizesize very smallvery small much largermuch larger

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(1 (1 –– 5 5 μμm)m) (10 (10 –– 100 100 μμm)m)complexitycomplexity relatively simplerelatively simple more complexmore complexcell wallcell wall usually present usually present

(contains (contains peptidoglycan)peptidoglycan)

sometimes sometimes present (lacks present (lacks peptidoglycan)peptidoglycan)


ProkaryotesProkaryotes EukaryotesEukaryotesplasma plasma membranemembrane

always presentalways present always presentalways present

internal internal bb

may contain may contain i f ldi fi f ldi f

complex system complex system f i lf i l

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membranesmembranes infoldings of infoldings of the plasma the plasma membrane but membrane but usually lack usually lack internal internal membranesmembranes

of internal of internal membranes membranes divides cell into divides cell into specialized specialized compartmentscompartments


ProkaryotesProkaryotes EukaryotesEukaryotesmembranemembrane--bound bound organellesorganelles

absentabsent presentpresent

ribosomesribosomes smaller andsmaller and larger andlarger and

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ribosomesribosomes smaller and smaller and free in the free in the cytoplasmcytoplasm

larger and larger and may be bound may be bound to ERto ER

cytoskeletoncytoskeleton absentabsent presentpresentflagellaflagella solid flagellin; solid flagellin;

rotaterotatemicrotubules; microtubules; bendbend


ProkaryotesProkaryotes EukaryotesEukaryotesstructure structure of genetic of genetic materialmaterial

single, naked, single, naked, circular DNA circular DNA moleculemolecule

many linear many linear chromosomes, chromosomes, each made of 1 each made of 1 DNA moleculeDNA molecule

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DNA molecule DNA molecule joined with proteinjoined with protein

location location of genetic of genetic materialmaterial

in an area of in an area of the cytoplasm the cytoplasm called the called the nucleoidnucleoid

inside a inside a membranemembrane--bound bound nucleusnucleus


Name and describe the types Name and describe the types of surface markers that give of surface markers that give

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ggcells identity.cells identity.


Cell surface markers allow the cells of Cell surface markers allow the cells of a multicellular organism to recognize a multicellular organism to recognize each other and to distinguish “self” each other and to distinguish “self” from “nonfrom “non--self.”self.”

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In this section, we will examine 2 types In this section, we will examine 2 types of cell surface markers:of cell surface markers:

GlycolipidsGlycolipidsMHC proteinsMHC proteins

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Glycolipids:Glycolipids:Are lipids embedded in the plasma Are lipids embedded in the plasma membrane with cabohydrate groups membrane with cabohydrate groups attachedattached

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Allow cells that are part of the same Allow cells that are part of the same tissue to recognize each other and tissue to recognize each other and form intimate connections to better form intimate connections to better coordinate their functions.coordinate their functions.


MHC proteins:MHC proteins:Are proteins embedded in the surface Are proteins embedded in the surface of the plasma membrane.of the plasma membrane.Allow cells of the immune system to Allow cells of the immune system to

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ow ce s o t e u e syste toow ce s o t e u e syste todistinguish foreign cells from the distinguish foreign cells from the body’s own cells so they can mount an body’s own cells so they can mount an attack against any foreign cells.attack against any foreign cells.


Explain what cell junctions are, and Explain what cell junctions are, and discuss the following types of cell discuss the following types of cell junctions:junctions:

a)a) tight junctiontight junction

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g jg jb)b) anchoring junctionanchoring junctionc)c) communicating junctioncommunicating junction


Cell junctionsCell junctions refer to longrefer to long--lasting lasting or permanent connections between or permanent connections between adjacent cells.adjacent cells.

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We will examine 3 types of cell We will examine 3 types of cell junctions:junctions:

Objective 8aObjective 8a

a)a) Tight junctionsTight junctions connect cells into connect cells into sheets. Because these junctions sheets. Because these junctions form a tight seal between cells, in form a tight seal between cells, in order to cross the sheet, order to cross the sheet,

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,,substances must pass through the substances must pass through the cells, they cannot pass between cells, they cannot pass between the cells.the cells.


a.

Tight junction

Adjacent plasmamembranes

Tight junctionproteins

Intercellularspace

MicrovilliMicrovilli

TightjunctionTightjunction

2.5 µm

Basal laminaBasal lamina

Anchoringjunction(desmosome)


IntermediatefilamentIntermediatefilament

CommunicatingjunctionCommunicatingjunction

Courtesy of Daniel Goodenough

Tight Junction

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Objective 8bObjective 8b

b)b) Anchoring junctionsAnchoring junctions attach the attach the cytoskeleton of a cell to the cytoskeleton of a cell to the matrix surrounding the cell, or to matrix surrounding the cell, or to the cytoskeleton of an adjacentthe cytoskeleton of an adjacent

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the cytoskeleton of an adjacent the cytoskeleton of an adjacent cell.cell.


Intercellular space


C dh in

Anchoring junction (desmosome)MicrovilliMicrovilli


Anchoring Junction

b.

Cadherin

Cytoplasmicprotein plaque

Cytoskeletal filamentsanchored to plaque






0.1 µm

© Dr. Donald Fawcett/Visuals Unlimited.

Objective 8cObjective 8c

c)c) Communicating junctionsCommunicating junctions link link the cytoplasms of 2 cells the cytoplasms of 2 cells together, permitting the together, permitting the controlled passage of small controlled passage of small

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p gp gmolecules or ions between them. molecules or ions between them. In animals, these junctions are In animals, these junctions are called called gap junctionsgap junctions; in plants ; in plants they are called they are called plasmodesmataplasmodesmata..


MicrovilliMicrovilli


Communicating Junction

c.

Intercellular space

Channel (diameter 1.5 nm)

Communicating junction

Connexon

Two adjacent connexonsforming an open channelbetween cells







1.4 µm

© Dr. Donald Fawcett/Visuals Unlimited.

Plasmodesmata connect plant cellsPlasmodesmata connect plant cells

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Table 4.4Table 4.4