Cell : The Unit of Life

All living things are made from one or more cells. A cell is the simplest unit of life and they are responsible for keeping an organism alive and functioning. This lesson to cells is the starting point for the area of biology that studies the various types of cells and how they work.

In this lesson you will learn about :
1) What is a Cell?
2) The Invention of the Microscope and the Discovery of Cell.
3) Cell Theory.
4) Cells - Number, Size, Shape and Function.
5) Structure of a Cell
6) Prokaryotic and Eukaryotic Cells.
7) The Plant and Animal cells.
8) Stem Cells.

I hope this document is helpful to you. Please share the document with your friends if you think this will benefit them. Get ready for the next lesson. Thanks.

1. Cell : The Unit of Life

2. What is a Cell ?
Thecellisthefundamentalstructuraland
functionalunitofalllivingbeings.
Alllivingthingsaremadeofoneormorecells.
Everycellhasitsownlife.
Oldandweakcellsinthebodycontinuallydieand
arereplacedbynewcells.
Allorganismsincludingourselves,startlifeasa
singlecellcalledthezygote.
Cellsaresosmall(microscopic)thattheycannot
beseenwiththenakedeye.
BiswarupMajumder| Bio-World 1

3. The Invention of the Microscope
BiswarupMajumder| Bio-World
ThefirstmicroscopewasconstructedbyDutch
scientistAntonieVanLeeuwenhoek(1632-1723).
Allhismicroscopesconsistedofasinglebiconvex
lensandwerecalledsimplemicroscopes.
Someofthesemicroscopeshadaconsiderable
magnifyingpowerupto200times.
Lens
Sample
Holder
Focus
Knob
AntonieVan Leeuwenhoek
Leeuwenhoek’s Simple
Microscope
2

4. The Discovery of Cell
BiswarupMajumder| Bio-World
RobertHooke(1635-1703),anEnglishscientist,
developamicroscopebyusingtwolensesfor
achievinggreatermagnification.Suchmicroscopes
werelaterknownascompoundmicroscopes.
Hookeexaminedathinsliceofcork(thedeadcells
ofoakbark)underhismicroscope.Henotedsmall
geometricshapeswhichhenamedcellsbecause
theyremindedhimofthesmallroommonkslived
inatamonastery.
Robert Hooke
Drawing by Hooke
Hooke’s Microscope
3

5. An Ordinary Compound Microscope
BiswarupMajumder| Bio-World
Theordinarycompoundmicroscopeoftodayis
greatlyimproveddesignoftheoriginalHooke’s
microscope.
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6. Electron Microscope
BiswarupMajumder| Bio-World
Anelectronmicroscopeisamicroscopethatusesa
beamofacceleratedelectronsasasourceof
illumination.
ElectronMicroscopescanhavemagnifications
of×500000.
ErnstRuskaandMaxKnollbuiltthefirstelectron
microscopein1931.Forthisandsubsequentwork
onthesubject,ErnstRuskawasawardedthe
NobelPrizeforPhysicsin1986.
Pollen Grain
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7. Light vs. Electron Microscope
BiswarupMajumder| Bio-World
Electron Microscope
Light Microscope
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8. CellTheory
BiswarupMajumder| Bio-World
ThethreeBasicComponentsoftheCellTheory:
1.Allorganismsarecomposedofoneormore
cells[Schleiden&Schwann(1838-39)].
2.Thecellisthebasicunitoflifeinallliving
things[Schleiden&Schwann(1838-39)].
3.Allcellsareproducedbythedivisionof
preexistingcells.[Virchow(1858)].
Matthias Schleiden
Theodor Schwann
Rudolf Virchow
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9. BiswarupMajumder| Bio-World
Cells–How Numerous ?
Cells–How Small ?
Mycoplasmagallicepticum,aparasiticbacteriumwhichlives
intheprimatebladder,wastedisposalorgans,genital,and
respiratorytracts,isthoughttobethesmallestknown
organismcapableofindependentgrowthandreproduction.
ThelargestcellfoundinnatureisanOstrichEgg.
Nervecellsarethelongestcell.Thelongestofnervecells
inanyspeciesarebefoundinthecolossalsquid,withsome
nervecellsestimatedtobeover10metersinlength.
Unicellular Organisms MulticellularOrganisms
8
Did You Know ?

10. BiswarupMajumder| Bio-World
Why are cells so small ?
Smallcellsizeisapracticalnecessityarisingfromthe
decreaseinthesurfacearea-to-volumeratioofany
objectasitincreasesinsize.Asanobjectincreasesin
volume,itssurfaceareaalsoincreases,butnotas
quickly.
Thisphenomenonhasbiologicalsignificancefortwo
reasons:
1.Thevolumeofacelldeterminestheamountof
metabolicactivityitcarriesoutperunitoftime.
2.Thesurfaceareaofacelldeterminestheamount
ofsubstancesthatcanenteritfromtheoutside
environment,andtheamountofwasteproducts
thatcanexittotheenvironment.
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11. BiswarupMajumder| Bio-World
CellShapes & Functions
RBC
WBC
Nerve Cell
Striated Muscle Fibre
Guard Cell
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12. BiswarupMajumder| Bio-World
Structure of a Cell
Cell
Cell Boundaries Protoplasm
Cell Wall
Cell Membrane Cytoplasm Nucleus
Cellular
Organelles
Vacuoles Cytoplasmic
Inclusions
Membrane -BoundMembrane -Less
Ribosome
Centrosome
Double-Membranous
Single-Membranous
Mitochondria
Plastid
Endoplasmic reticulum
Lysosome
Golgi apparatus
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13. BiswarupMajumder| Bio-World
Cell Boundaries
12

14. BiswarupMajumder| Bio-World
Cell Wall
Cellwallisatough,rigidlayerthatsurroundssometypes
ofcells.Itislocatedoutsidethecellmembranewhose
mainfunctionistoproviderigidity,strength,protection
againstmechanicalstressandinfection.
Cellwallisacharacteristicfeaturetocellsofplants,
bacteria,fungi,manyalgaeandsomearchaea.Protozoans
andanimalsdonothaveacellwall.
Thecompositionofthecellwalldiffersfromonespecies
totheother.
TheArcheancellwallismadeofglycoproteinsand
polysaccharides.Infungicellwallsaremadeof
glucosamineandchitin.Inalgaeitiscomposedof
glycoproteinsandpolysaccharides.Theplantcellwallis
mainlycomposedofcellulose,hemicellulose,glycoproteins,
pectinsandlignin.
Freelypermeableandnon-livinginnature.
Thecellwallislikeafort;it
protectstheorganellesinside
thecell,andprovidesstrength
andsupport.
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15. BiswarupMajumder| Bio-World
Plant Cell Wall
Themiddlelamella-Itisfirstlayerformedduringcell
division.Thislayerisrichinpectin.Itistheoutermost
layer,joinstogetheradjacentplantcellsandholds
themtogether.
Theprimarycellwall-Itisformedafterthe
middlelamella.Itiscomposedofpectincompounds,
hemicelluloseandglycoproteins.Thelayerconsistsofa
frameworkofcellulosemicro-fibrils,inagel-like
matrix.Itisthin,flexibleandextensiblelayer.
Thesecondarycellwall-Itisathicklayerformed
insidetheprimarycellwall.Itisextremelyrigidand
providesstrength.Itiscomposedofcellulose,
hemicelluloseandlignin.
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Plantcellwallconsistsofthreelayers:theprimarycell
wall,secondarycellwallandthemiddlelamella.

16. Bacterialcellwall:
Thegrampositivebacteriahaveathickcellwallandismadeupofmanylayersof
peptidoglycanandteichoicacids.
BiswarupMajumder| Bio-World
Bacterial & Fungal Cell Wall
Thegramnegativebacteriahavethinnercellwalls,andismadeupoffewlayersof
peptidoglycansandissurroundedbyalipidmembranecontaininglipopolysacccharidesand
lipoproteins.
Madeupofpeptidoglycansalsoknownasmurein.The
cellwallofbacteriaisessentialforthesurvivalof
bacteria.
Cellwallofbacteriaisbroadlyclassifiedintotwotypes:
grampositiveandgramnegative.
Fungicellwallconsistsofchitinandotherpolysaccharides.
Speciesoffungithatpossessacellwallhaveaplasma
membraneandthreelayersofcellwallmaterialsurrounding
it.Theselayersaremadeupofchitin,glucansandalayera
ofmannoproteins(mannosecontainingglycoproteins).
Fungalcellwall:
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17. BiswarupMajumder| Bio-World
Cell Wall -Functions
1.Givesthecelladefiniteshapeandstructure.
2.Providesstructuralsupport.
3.Protectionagainstinfectionandmechanicalstress.
4.Separatesinteriorofthecellfromtheouterenvironment.
5.Itenablestransportofsubstancesandinformationfrom
thecellinsidestotheexteriorandviceversa.
6.Alsohelpsinosmotic-regulation.
7.Preventswaterloss.
8.Thephysiologicalandbiochemicalactivityofthecellwall
helpsincell-cellcommunication.
9.Itpreventsthecellfromrupturingduetoturgor
pressure.
10.Aidsindiffusionofgasesinandoutofthecell.
Plasmodesmata: The Bridge To Somewhere
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18. BiswarupMajumder| Bio-World
Cell Membrane
Itistheboundary,whichseparatesthelivingcellfrom
theirnon-livingsurroundings.
Inanimalcells,theplasmamembraneispresentinthe
outermostlayerofthecellandinplantcellitispresent
justbeneaththecellwall.
Verythin,flexible,livingmembrane,possessesfinepores.
Composedoftwolayersofphospholipidsandembedded
withproteins.
Itisathinsemipermeablemembranelayer,which
allowsonlyselectedmoleculestodiffuseacrossthe
membrane.
Membrane Transport
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19. BiswarupMajumder| Bio-World
Cell Membrane
Structure:
1.Separatescontentsofthecellfromitssurroundings.
2.Regulatestheentryofcertainsolutesandions.
3.Maintaintheshapeofthecell(inanimalcell).
Chief Functions:
Itisthephospholipidsbilayer.
Plasmamembraneisanamphipathic,whichcontainsboth
hydrophilicheadsandhydrophobictails.
Itisafluidmosaicoflipids,proteinsandcarbohydrate.
Itislipidbilayer,whichcontains-twolayersof
phospholipids,phosphateheadispolar(waterloving),
fattyacidtailsnon-polar(waterfearing)andthe
proteinsembeddedinmembrane.
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Fluid mosaic model of acell membrane bySJ SingerandGL Nicolsonin 1972

20. BiswarupMajumder| Bio-World
Cell Wall vs. Cell Membrane
Cell Wall Cell Membrane
Itisarigid,thickstructure
and visibleinlight
microscope.
Itisdelicate,thinstructure
andvisibleonlyinelectron
microscope.
Itisoutermostlayerinplant
cellandoccursasa
protective covering
surroundingthe plasma
membrane.
Itistheoutermostlayerin
animalcellandoccursasa
semi-permeable covering
surroundingtheprotoplasm.
Cellwallismadeupof
celluloseinplantcell.
Cellwallismadeupof
peptidoglycaninbacteria.
Cellwallismadeupofchitin
infungi.
Plasmamembraneismadeup
oflipids,proteinsandsmall
amountofcarbohydrates.
Itiscompletelypermeableto
ordinarymacromolecule.
Itisselectivelypermeable
i.e.allowingonlycertain
moleculestopass.
Itoccursinplantcell,
bacteriumandfungus.
Itoccursinallcells.
Itismetabolicallyinactive
andnon-living.
Itismetabolicallyactiveand
living.
Itdeterminesthecellshape
andoffersprotection.
Itprotectsprotoplasmand
maintainsaconstantinternal
environment to the
protoplasm.
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21. BiswarupMajumder| Bio-World
Protoplasm
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[Cytoplasm + Nucleus]

22. BiswarupMajumder| Bio-World
Protoplasm
✓Thelivingcomponentofacell.
✓Protoplasm=Cytoplasm+Nucleus.
✓Surroundedbytheplasmamembrane.
✓Plantcellshaveanouterboundarycalledthecellwall.
Cytoplasm
✓Jellylikesubstanceenclosedbycellmembrane.
✓Containsorganellestocarryoutspecificjobs.
✓Providesamediumforchemicalreactionstotakeplace.
Nucleus
✓Thecellnucleusactslikethebrainofthecell.
✓Containsgeneticmaterial.
Components
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23. BiswarupMajumder| Bio-World
Nucleus
22

24. BiswarupMajumder| Bio-World
Structure of Nucleus
NuclearEnvelope
▪Itisadouble-layeredmembranethatenclosesthe
contentsofthenucleusduringmostofthecell’s
lifecycle.
NuclearPores
▪Thenuclearenvelopeisperforatedwithholescalled
nuclearpores.
▪Theseporesregulatethepassageofmoleculesbetween
thenucleusandcytoplasm,permittingsometopass
throughthemembrane,butnotothers.
Nucleoplasm
▪Alsocallednuclearsaporkaryoplasm,isthefluid
usuallyfoundinthenucleusofeukaryoticcells.
▪Thefluidcontainsprimarilywater,dissolvedions,anda
complexmixtureofmolecules.
▪Itsprimaryfunctionistoactasasuspensionmedium
fortheorganellesofthenucleus.
Nucleolus
▪Thenucleolusisamembrane-lessorganellewithinthe
nucleusthatmanufacturesribosome,thecell’sprotein-
producingstructures.
Chromatin
▪FibresofDNAandprotein,storesinformationfor
synthesisofproteins.
▪Whencellpreparestodivide,chromatinfibrescoilup
asseparatestructures,chromosomes.
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25. BiswarupMajumder| Bio-World
Nucleus
▪Itregulatesandcoordinatesvariouslifeprocessesof
thecell.
▪Itplaysanimportantpartincelldivision.
▪Itcontainsfactors(genes)whichdetermineheredity.
Structure
Chief Functions:
The nucleus is called the "brain” of the cell because it holds the
information needed to conduct most of the cell's functions.
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26. BiswarupMajumder| Bio-World
A gene is the
basic physical and
functional unit of
heredity. Genes,
which are made up
of DNA, act as
instructions to
make molecules
called proteins.
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27. Chromosome Number
BiswarupMajumder| Bio-World
Likethefingerprints,theDNApatternhelpsinascertainingtheidentifyofa
personandhencethetermDNAfingerprinting.Thetechniquecaneven
testifythepercentageofanindividual.Inawoman’smurdercaseinDelhiin
July1995theDNAfromherunidentifiablecharreddeadbodywasmatched
withtheDNAfromthebodycellsofherparentstoconfirmthattheyreally
werethefatherandmotherofthemurderedwoman.Thatwasoneofthe
earliestcases.Now,DNAfingerprintinghasbecomeverycommon.
DNA -Fingerprinting
26

28. BiswarupMajumder| Bio-World
Prokaryotic vs. Eukaryotic Cells
Eukaryotic CellProkaryotic Cell
27

29. BiswarupMajumder| Bio-World
Cell Organelles
28

30. Mitochondria -Structure
BiswarupMajumder| Bio-World
Outermembrane
▪Itissmoothandiscomposedofequalamountsof
phospholipidsandproteins.
▪Ithasalargenumberofspecialproteinsknownas
theporins.
▪Theporinsareintegralmembraneproteinsandthey
allowthemovementofmoleculesthatareof5000
daltonsorlessinweighttopassthroughit.
▪Theoutermembraneisfreelypermeabletonutrient
molecules,ions,energymoleculesliketheATPand
ADPmolecules.
Innermembrane
▪Theinnermembraneofmitochondriaismore
complexinstructure.
▪Itisfoldedintoanumberoffoldsmanytimesandis
knownasthecristae.
▪Thisfoldinghelptoincreasethesurfaceareainside
theorganelle.
▪Thecristaeandtheproteinsoftheinnermembrane
aidsintheproductionofATPmolecules.
▪Variouschemicalreactionstakesplaceintheinner
membraneofthemitochondria.
▪Unliketheoutermembrane,theinnermembraneis
strictlypermeable,itispermeableonlytooxygen,
ATPanditalsohelpsinregulatingtransferof
metabolitesacrossthemembrane.
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31. Mitochondria -Structure
BiswarupMajumder| Bio-World
Intermembranespace
▪Itisthespacebetweentheouterandinner
membraneofthemitochondria,ithasthesame
compositionasthatofthecell'scytoplasm.
▪Thereisadifferenceintheproteincontentinthe
intermembranespace.
Matrix
▪Thematrixofthemitochondriaisacomplex
mixtureofproteinsandenzymes.Theseenzymes
areimportantforthesynthesisofATPmolecules,
mitochondrialribosomes,tRNAsandmitochondrial
DNA.
30

32. Mitochondria -Functions
BiswarupMajumder| Bio-World
Themostimportantfunctionofthemitochondriaisto
produceenergy.Thesimplermoleculesofnutritionare
senttothemitochondriatobeprocessedandtoproduce
chargedmolecules.Thesechargedmoleculescombinewith
oxygenandproduceATPmolecules.Thisprocessisknown
asoxidativephosphorylation.
Mitochondriahelpthecellstomaintainproper
concentrationofcalciumionswithinthecompartmentsof
thecell.
Themitochondriaalsohelpinbuildingcertainpartsof
bloodandhormonesliketestosteroneandestrogen.
Thelivercellsmitochondriahaveenzymesthatdetoxify
ammonia.
Themitochondriaalsoplayimportantroleintheprocessof
apoptosisorprogrammedcelldeath.Abnormaldeathof
cellsduetothedysfunctionofmitochondriacanaffect
thefunctionoforgan.
31
Cellular
Respiration

33. Plastid -Types
BiswarupMajumder| Bio-World
Chloroplastsareelongateddiscshapedorganelleswhichcontains
chlorophyll.Chlorophyllispresentingreenplantswhichhelps
themmakefoodbytheprocessofphotosynthesis,whichuses
energyfromthesunlightisconvertedintochemicalenergy.
Chromoplastsareplastidswhicharefoundinfruitsandare
yellow,orangeandredincolor.
Lecuoplastsarecolorlessplastids.Theyfoundinroots,seedsand
undergroundstems.
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34. Chloroplast -Structure
BiswarupMajumder| Bio-World
Theyhaveadoublemembranestructure.
TheyhavetheirownDNA(circularandnaked)andribosomes
(70S).
Thylakoids–flatteneddiscshaveasmallinternalvolumeto
maximisehydrogengradientuponprotonaccumulation
Grana–thylakoidsarearrangedintostackstoincreaseSA:Vol
ratioofthethylakoidmembrane
Photosystems–pigmentsorganisedintophotosystemsin
thylakoidmembranetomaximiselightabsorption.
Stroma–centralcavitythatcontainsappropriateenzymesand
asuitablepHfortheCalvincycletooccur.
Lamellae–connectsandseparatesthylakoidstacks(grana),
maximisingphotosyntheticefficiency.
33

35. The EndosymbioticTheory
BiswarupMajumder| Bio-World 34
Endosymbiosis(Greek:endon="within",sym=
"together"andbiosis="living").
Anendosymbiontisanyorganismthatliveswithinthe
bodyorcellsofanotherorganism.
Theendosymbiosistheoryattemptstoexplainthe
originsoforganellessuchasmitochondriaand
chloroplastsineukaryoticcells.
AccordingtoEndosymbiosistheory:
Moderneukaryoticcellsevolvedfromsimple,phagotrophic
cellsthatingestedbacteriaandcyanobacteria;thepreywas
notdigested,andphysiologicalprocessesofthe
endosymbiontswereusedbythehost.

36. Endoplasmic Reticulum
BiswarupMajumder| Bio-World
Theendoplasmicreticulum(ER)isanetworkof
interconnectingmembranesdistributedthroughoutthe
cytoplasm.
Theinternalcompartment,calledthelumen,isaseparate
partofthecellwithadistinctproteinandioncomposition.
Atcertainsites,theERmembraneiscontinuouswiththe
outernuclearenvelopemembrane.
Dependinguponthepresenceorabsenceofribosomeson
thesurface,therearetwotypesofE.R.
1.RoughE.R.–presenceofribosomesonitssurface.
2.SmoothE.R.–devoidofribosomesonitssurface.
35
Structure:

37. Endoplasmic Reticulum
BiswarupMajumder| Bio-World 36
Types:
Functions:

38. Golgiapparatuswasdiscoveredintheyear1898byan
ItalianbiologistCamilloGolgi.
Inplantcells,theGolgiapparatusiscalleddictyosome.
Itislocatedinthecytoplasmnexttotheendoplasmic
reticulumandnearthecellnucleus.
Golgi Apparatus
BiswarupMajumder| Bio-World 37
Structure:
TheGolgiapparatusorganelleconsistsofthree
membranouscomponentsthatcanbeclearlyidentified
throughtheelectronmicroscope.Thesearelamellaeor
cisternae,vesiclesandvacuoles.
Theflatsacsofthecisternaearestackedandisbent
andsemicircularinshape.
TheGolgicomplexispolarinnature:Oneendofthe
stackisknownasthecisface,itisthe'receiving
department"whiletheotherendisthetransfaceandis
the"shippingdepartment“.
VesiclesareminutesphericalstructuresoftheGolgi
apparatusthatoriginatefromcisternaebybuddingor
“pinchingoff”process.Theyarefoundsinglyorin
clusters.
Vacuolesarespherical,comparativelylargersecretory
granulesadjacenttocisternae.Theyalsolieatmaturing
faceandcontainelectron-densematerial.
A Golgi Body is like a “Post Office” because a Post Office
collects and packages packagesjust like how a Golgi Body
modifies, collects and packages.

39. Golgi Apparatus
BiswarupMajumder| Bio-World 38
Theprincipalfunctionofgolgiapparatusorganelleis
secretionthatoccursintheformofsecretorygranules.I
talsohasaroleinneurosecretionsecreting
neurosecretorymaterials.
Thegolgiapparatusorganelleactsasapackaging
organelleandtransportsvariousmaterialslikeproteins,
polysaccharidesoutofthecell.
Thegolgiapparatustakespartintheformationofplasma
membrane,cellwall,lysosomes(primarylysosomes),
acrosome(headcap)ofsperm.
Functions:
Structure

40. Lysosome
BiswarupMajumder| Bio-World 39
Thecytoplasmofbothplantandanimalcellscontain
manytinyregularshapedmembraneboundvesicles
knownaslysosomes.
Theycontainvarious(atleast50types)hydrolytic
enzymes.
Lysosomesofinjuredordeadcellsrupturetogether
andreleaseenzymeswhichlysetheuselesscells.
ThesearemembranoussacsbuddedofffromGolgi
apparatus.
Lysosomeshelp in digestion. Lysosomescan digest the entire cell
.This takes place during formation of human appendages and
during natural death of cells. Hence it is termed as"Suicidal
bag“.

41. Lysosome-Types
BiswarupMajumder| Bio-World 40
Primarylysosomes:Thenewlyproducedlysosomesare
calledprimarylysosomes,whichisavirginparticleinthat
itsdigestiveenzymeshavenotyettakenpartinhydrolysis.
Secondarylysosomes:Thelysosomesthatisformedby
fusionofprimarylysosomeandphagosomesistermed
secondarylysosomes.Theyareoftwotypes-Hetero
Phagosomesaresecondarylysosomesformedby
endocytosedphagosomesandprimarylysosomes.Lysogenic
digestion of endocytosed material is
termedheterophagy.Autophagosomesareformedby
fusionofcellularparticlesandprimarylysosomes.The
processofdigestionofportionofacell'sowncytoplasmic
constituentsbyitslysosomesistermedautophagy.
Residualbodies:HeteroPhagosomesandautophagosomes
afterdigestionandabsorptionareleftwithonlyresidues
anddenaturedenzymeswithinthevacuole,whichare
termedresidualbodies.
Onthebasisoffunctionoflysosomes,theyare
classifiedintothreetypes:

42. BiswarupMajumder| Bio-World 41
EndomemebraneSystem
Dividescellintocompartments.
Includes:
EndoplasmicReticulum(andvesicles).
GolgiApparatus(andvesicles).
Lysosomes.
Vacuoles.
Responsibleforproductionofvariousmacromolecules,
includingproteinsandsomelipids.
Important note : The endomembranesystem does not
include mitochondria, chloroplasts, or peroxisomes.

43. RibosomescontainequalamountofproteinsandrRNA.So
theyarealsoknownasribonucleoprotein.
Ribosomesfunctionsintwocytoplasmiclocations.
FreeRibosomes:Theyaresuspendedinthecytoplasm.
BoundRibosomes:Theyareattachedtotheoutsideofthe
endoplasmicreticulum.
Eachribosomehastwosubunits.
Theribosomesofprokaryotesaresmallerthaneukaryotes.
Theyaredifferentintheirmolecularcomposition.
Ribosome
BiswarupMajumder| Bio-World 42

44. Ribosome -Function
BiswarupMajumder| Bio-World
Theribosomeplaysakeyroleintranslatingthegenetic
message.ThisgeneticmessageiscarriedbymRNAfrom
thenucleustothecytoplasm.Thismessageistranslatedin
theribosomes.Itformsspecificprimarystructure(amino
acidsequence)ofapolypeptidechain.
43

45. Centrosome
BiswarupMajumder| Bio-World
Thecentrosomeisanorganellemadeupoftwomutually
perpendicularstructuresknownascentrioles.
Eachcentrioleiscomposedof9equallyspacedperipheral
fibrilsoftubulinproteinandthefibrilisasetof
interlinkedtriplets.Thecorepartofthecentrioleisknown
asahubandisproteinaceousinnature.Thehubconnects
theperipheralfibrilsviaradialspokewhichismadeupof
proteins.
Thecentriolesformspindlefibersduringcelldivision.
44
(a)Howcentriolesareacomponent
ofcentrosomes.
(b)Howcentrosomesareinvolvedin
celldivision.
(c)Ultrastructureofcentriolesas
seeninT.S.
(C)

46. BiswarupMajumder| Bio-World
Vacuoles
45

47. Vacuoles
BiswarupMajumder| Bio-World
Theterm“Vacuole”literallymeansemptyspace.
Vacuolesareformedbythefusionofsmallmultiple
membranevesicles.
Theyhavenobasicshapeorsize,andtheirstructure
variesaccordingtoneedsofcell.
Plantandfungalcellsusuallyconsistoflargevacuoles
althoughtherenumberisless,onthecontraryanimaland
bacterialcellsmightcontainlargenumberofsmall
vacuoles.
Tonoplastatermcommonlyassociatedwithvacuoles
referstoaveryactiveanddynamicmembranethat
surroundstheplantcellvacuole.
Functions
46

48. BiswarupMajumder| Bio-World
CytoplasmicInclusions
47

49. CytoplasmicInclusions
BiswarupMajumder| Bio-World
Types
Thesearediverseintracellularnon-livingsubstances
thatarenotabletocarryoutanymetabolicactivity
andarenotboundbymembranes.
ThesestructureswerefirstobservedbyO.F.Müllerin
1786.
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50. Plant Cell vs. Animal Cell
BiswarupMajumder| Bio-World 49

51. Stem Cells
BiswarupMajumder| Bio-World 50