2 Plant Cell physiology and their role tt

plant cell phisiology

1. Cell Physiology

2. Plant Cell:
•CellisthebasicStructuralandfunctionalunitoflivingorganism.It
consistsofmicroscopicmassofprotoplasmsurroundedbyacell
membrane.
•Itisthesmallestunitthatcancarryonalltheprocessoflife.
•Inaunicellularorganisms,thesinglecellperformsallmetabolicfunctions
suchasgrowth,respiration,reproduction,digestion,excretion,etc.
•Inmulticellularorganismsallthevitalactivitiesaretheresultofcombined
actionofthesecells.Hence,cellisconsideredasabasicunitoflife.
•Fromthephysiologicalpointofview,aplantcellmaybedefinedasan
organizedmassofprotoplasmconstitutingthephysiologicalunitofthe
plant,capableofexhibitingallthecharacteristicsoflife.

3. Structure of plant cell:

4. •Plant cells are usually rectangular in shape.
•In a plant cell the cell membrane forms the outermost covering of the cytoplasm
beneath cell wall.
•The protoplasm consists of the cytoplasm and the nucleus.
•The cytoplasm consists several living organelles and non-living inclusions.

6. Thestructureofplantcellcanbedescribedunderfollowingheadings:
1.Cellwall:
•Thecellwallsofplantsaregenerallythick,strong,porous,rigidandnon-living
structures,whichenclosethecellsincludingtheplasmamembranes.
•Cellwallissecretedbythelivingmatterofcell.
•Cellwallishighlypermeabletowater,solutesandgases.
•Thisstructuremakingtheoutermostboundaryofthecell,isknownasextra
cellularmatrix(ECM).
•Thecellwallisprimarilymadeupofcelluloseandpectin,butsomeadditional
materialsaredepositedforspecificfunctions.
Structure of cell wall:
The cell wall of a mature plant cell consists of:-
1.Primary wallis the first formed wall. It is thin, permeable, elastic(only semi
rigid) and capable of growth.

7. 2. Secondary wall-After maturity, more
layers of cells are added on the inner side
of the primary wall formed secondary cell
wall .
3. Middle lamella-It is the first structure
that is formed from cell plate between the
newly formed daughter cells at the time of
cytokinesis

8. FunctionsofCellWall:-
•Cellwallprovidesshapeandrigiditytocell.
•Itprotectstheprotoplasmfromexternalinjury.
2.Cellmembrane(Plasmamembrane):
•Alllivingcellsareenclosedbyaselectivelypermeable,thinmolecularlayer
termedasplasmamembraneorplasmalemma.
•Theplasmamembraneseparatesthecellfromitssurroundings,protectsitfrom
changesinthechemicalandphysicalenvironment,andregulatesmovementsof
moleculesintoandoutofthecell.
•ThestudyofplasmamembraneisbasedontheFluidMosaicModel.
•Toperformthefunctionoftheorganelle,plasmamembraneiscomposed
primarilyoftwotypesofmolecules—lipids,whicharefattyoroilymolecules,
andproteins.
•Allmembraneshaveacommongeneralstructureinwhichtwolayeredsheetsor
bilayeroflipidmoleculeshaveproteinsembeddedinthem.
•Themostcommonlipidsintheplasmamembranearethephospholipid,which
hasapolar(hydrophilicitcanmixwithwater)headandtwononpolar
(hydrophobictheydonotmixwellwithwater)tails.

9. •Intheplasmamembrane’sbilayerconstruction,phospholipidmoleculesare
arrangedsothattheirhydrophilicheadspointoutwardoneithersideofthe
membrane,andtheirhydrophobictailspointtowardeachotherinthemiddle
ofthemembrane.
•Bybridgingboththehydrophilicandhydrophobicregionsofthemembrane,
theseproteinsare"bound"tothemembrane.
•Mostinterestingly,however,isthatthesebridgingproteinscanformchannels
throughthemembraneforaparticularkindofchemicaltopass.
•Thecarbohydratesoccuronlyattheoutersurfaceofthemembrane.
Functionofplasmamembrane:
•Cellmembraneofthecellistheimportantimport/exportcontrolarea.Itcan
"pump"othersubstanceintothecellagainsttheconcentrationgradientor
pumpother"wastes"etc.outofthecellisknownMembranetransport.The
differencebetweentheconcentrationofasubstanceintwodifferentareasis
knownasaconcentrationgradient.
•Inmulticellularorganisms,theplasmamembranealsoplaysacriticalrolein
communicationbetweencells.

11. 3.Cytoplasm:
•Itisahomogeneous,mostlyclearjelly-likeliquidliesbetweenthenucleusand
cellmembrane,consistingofcytosolandthecellularorganelles.
•Cytosoliscomposedofwater,salts,organicmolecules,andthemanyenzymes
necessaryforthecelltocatalyzereactions.
•80%ofthecytoplasmisaqueousandcomposedofionsandsoluble,primarily
organic,macromolecules.
•The20%ofthecytoplasmthatisnotaqueousismadeupoforganelles,
mitochondria,chloroplasts,vacuoles,thecytoskeleton,andendoplasmic
reticulum.
•Theaqueouspartisalsocalledhyaloplasm.
•Itbehaveslikeagelsometimes,dependingontheactivityphaseofthecell;inthis
state,itiscalledcytogel.Cytogellinestheplasmalemmaandknown
asectoplasm.
•Wheninsteaditbehaveslikealiquid,it'scalledcytosol.Itisknownasendoplasm..

12. 4.Vacuole:-
Avacuoleisalargefluid-filledsacinthecytoplasm,boundedbyasingle
membranecalledthetonoplast.
Vacuolesarefilledwithwateryfluidtermedascellsap.Itisacidic.
Thechemicalcompositionofcellsapdiffersmarkedlyfromthatofthe
surroundingcytoplasm.
Inmostcasesmatureplantcellshavesinglelargecentralvacuole.
Sothattheplantcytoplasmliesasathinlayerpositionedbetweentheplasma
membraneandthetonoplast.
Thevacuolecontainsnutrients,metabolites,pigmentsandwasteproducts.
Pigmentanthocyansarepresent,whichisresponsibleforthecolorsinflowers.
Functionofvacuole:-
1.structuralsupport,2.waterstorage;3.hydrolyticenzymes;4.osmoregulation
5.Storage,
6.TurgorPressure:waterentersthecell(cellvacuole)andcreatesturgorpressure.
Turgorpressuredrivescellgrowth.Openingandclosingofstomataisdueto
changesinturgorpressureofguardcellsThepressureappliedbythevacuole,
calledturgor,isnecessarytomaintainthesizeofthecell.Plantcellsdon't
increaseinsizebyexpandingthecytosplasm,rathertheyincreasethesizeof
theirvacuoles

13. 5.Lysosomes:
•Lysosomesareasinglemembraneboundsmallvesicularorganelles.
•Shapeandsizeoflysosomeisvariable.
•Agranulatedstromaandavacuolearelocatedinsidethemembrane.
•Lysosomesarefoundinfungiandroottipsofcells.
•Lysosomesarelittlesacsofhydrolyzingenzymes,acidhydrolasesthatareused
bythecelltobreakdownfoodaswellasdebrisandthebyproductsareusedin
biosyntheticactivityofcells..
•Thesesacsareseparatefromthecellbecausetheenzymescoulddestroythecell
iftheyweremixedwiththecytoplasm.
•Theenzymescontainedinthelysosomearesynthesizedonroughendoplasmic
reticulumandaretransportedtogolgibody.
•Itsfunctionsaredefenseagainstbacteriaandvirusesandindestroyingoldand
wornoutorganelles.Theyhavebeenfoundoccasionallytobedigestingthe
wholecellorpartofcell(autolysisorself-destruction);thereforelysosomesare
calledsuicidebags.

14. 6.Endoplasmicreticulum:
Someofthefloatingmembranesinthecytosolincludeanetworkoftinysacs,
tubulesandvesiclesthatinterconnectthroughouttheinsideofthecell.This
networkiscalledendoplasmicreticulum.
Accordingtothemetabolicactivitiesofcellendoplasmicreticulumassumes
threeformsindifferentcell:-

15. Endoplasmicreticulumisoftwotypes:-
1.Roughendoplasmicreticulum(R.E.R):Themembraneofendoplasmic
reticulumonitsexternalsurfacecarriesgranularstructuresknownas
ribosomes,theseregionsareknownasroughendoplasmicreticulumThese
ribosomesaremadeofproteinandRNAandareactivelyinvolvedinthe
synthesisofproteins.
2.Smoothendoplasmicreticulum(SER):Ithasatubularstructureandno
ribosomesattachedtothemembranesurface.Itconsistsofsmooth
membranesegmentsandfoundinregionspoorinproteinsynthesis.
Functionofendoplasmicreticulum:
Theendoplasmicreticulumneartheribosomesisresponsibleformovingmuch
oftheproteinthroughitstubulestootherpartsofthecell.andmaintainsthe
integrityofthemembranessurroundingthenucleus.
Thisistheconveyorbeltofthecell.
Thelargenetworkofendoplasmicreticulumprovideincreasedsurfacefor
enzymesyntheticactivity.

17. 7.Ribosomes:
•Ribosomesaresmall,nonmembranous,sphericalbodiesmainlyfoundbound
totheendoplasmicreticulumaswellasfreelyscatteredthroughoutthe
cytoplasm,inalltypesofcells.
•Ribosomesalwayshavetwosubunitswhichinterlockandbehaveasasingle
entity.
•Thelargersubunitsiscalledcornordome-shapedandthesmallersubunitis
cap–likeoroblate.
•Inplantcellthelargersubunitisof60stypeandsmallersubunitis40stype.
•Itiscomposedofapproximately60percentribosomalRNA(rRNA)and40
percentprotein.
•RibosomesaresometimesreferredtoassimplyRNA.
Functionofribosome:-
Ribosomesareactivelyinvolvedintheproteinsynthesis,theprocessthat
generatesorganictissue.Ribosomesarethusakindofprotein-synthesis
"machine."ThisprocessofusingtheinformationinRNAtomakeaproteinis
calledtranslation.

18. 8.GolgiApparatus(Golgicomplex,orGolgibodyorDictyosomes):
•TheGolgibodyconsistsofaseriesoffivetoeightcup-shaped,membrane-
bounded,flattenedsacscalledcisternae.
•TheGolgibodyaresurroundedbynumerous,small,membrane-bounded
vesicles.
•60cisternaemaycombinetomakeuptheGolgiapparatusinsomeunicellular
flagellatesandthenumberofGolgibodiesinacellvariesaccordingtoits
function.
•Thiscomplexisusuallylocatedclosetothecellnucleus.
Functionofgolgibody:-
•Itsfunctionsaresorting,modifying,andpackagingofmacro-moleculesthat
aresecretedbythecellorusedwithinthecellforvariousfunctions.
•TheGolgicomplexinplantcellsproducespectinandotherpolysaccharides
specificallyneededbyforplantstructureandmetabolism.
•AmongthemostimportantdutiesoftheGolgiapparatusistosortthewide
varietyofmacromoleculesproducedbythecellandtargetthemfor
distributiontotheirproperlocation.

20. 9.Mitochondria:
•Thesearerod-shaped,filamentousorgranularstructuresdistributedthrough
thecytosolofmosteukaryoticcells.
•Theirnumberwithinthecelldependsuponthemetabolicactivityofthatcell,
andmayrangefromasinglelargemitochondriontothousandsofthe
organelles.
Structure:
•Themitochondrionisboundbydoublelayered(outer&inner)membrane.
•Themembranesarelipo-proteininnature.
•Theoutermembraneissmoothbuttheinnermembranefoldsinwardsatplace
toformplatelikeorfingerlike,maybebranchedorunbranchedstructure,the
cristae.
•Thecristaeincreasesmetabolicsurfaceareaofthemitochondriaandcontains
allenzymesforkreb’scycle.
•Thecavityofmitochondrioncontainshomogenousgranularmatrix.Thematrix
containslipids,proteins,DNA,RNA,ribosomes,granulesandenzymes.

21. •Theoutersurfaceofoutermembraneandinnersurfaceofinnermembrane
containnumerousminutestructurescalledoxysomesorelementaryparticles.
•Theoxysomespresentontheoutersurfacearesimpleorglobular,whereasthe
oxysomespresentontheinnersurfacecontainabase,astalkandaspherical
head.
•Oxysomesareproteinaceousinnature.
•Thechemicalcompositionofmitochondriaonthedryweightbasisshows
protein(65-70%),lipid(25-30%),RNA(0.5%)andsmallamountofDNA.
Functionofmitochondria:
1.Themitochondriaarethecentersofrespiratoryactivityandcontainall
necessaryenzymes.
2.Kreb’scycletakesplaceinthemitochondriaduringwhichfoodmaterialis
completelyoxidizedintoCO
2andH
2O.
3.Theoxysomesliningthecristaeandinnermembranefunctionaselectron
carriersortransportersofhydrogenduringkreb’scycle.
4.Mitochondriacanalsosynthesizestructuralproteinsduetothepresenceof
DNAandRNA.
5.Mitochondriaareselfreplicatingandtheyarepassedonfromcelltocell.

22. Structure of Mitochondria
Oxysomes

23. 10.Plastids:-
•Theseareflat,circular,cytoplasmiccellorganelles,onlypresentinplantcells
andphotosyntheticorganisms.
•Theseareprimarilyinvolvedinformationandstorageofsolubleandinsoluble
carbohydrates.
•Plastidsaretwotypesonthebasispresenceorabsenceofpigment:-
A.Leucoplasts(plastidswithoutpigments):-
Storereservefoodmaterial,colorlessandoccurinthecellswhicharenot
exposedtosunlightandalsofoundinembryoniccells,meristematiccellsand
parenchymatouscells.
Leucoplastsarethecentersofstarch,oilsandproteinssynthesis.
Onthatbasisofstorage,leucoplastsareofthreetypes:
(a)Amyloplasts:-filledwithstarch
(b)elaioplasts:-storelipids
(c)aleuroplast(proteinoplast):-storeproteincrystalsandgranules

24. B.chromoplastsandchloroplasts(coloured):-
a.Chromoplasts:
Chromoplastsareplastidswithpigmentcoloursotherthangreen,theircolour
isduetotwopigments,caroteneandxanthophyll.
Yellow-to-redcoloredchromoplastsmanufacturecarotenoids.Theseare
presentinpetalsandfruits,impartingthemdifferentcolours(red,yellow
etc.).
Chromoplastsmaydevelopfromchloroplastsduetoreplacmentof
chlorophyllbyotherpigment.
Fore.g.greentomatoesandchiliesturnredonripeningduetochangeof
chlorophyllinchloroplastsbyredpigmentlycopinorlycopeneintomatoand
capsanthininchilies.

25. b.Chloroplasts:
Chloroplastsarethemostimportanttypeofplastidhavinggreen
pigment(chlorophyll),andaretypicallyabout10micrometersindiameter.
Theplastidsaremadeupofanouterlimitingmembraneandinnermatrix.
Theoutermembraneismadeupoftwolayersoflipoproteinandseparated
fromoneanotherbyaspaceknownasperplastidialspace.
Innermatrixofachloroplastisdifferentiatedintograna,wherelightreaction
ofphotosynthesistakesplaceandthestromawheredarkreaction(Calvin
cycle)iscompleted.
Granaconsistofthelamellarsystemandstromaisnon-membranousboth
consistofinterconnectedsaclikestructureknownasthylakoids.
Thylakoidsareoftwotypes(1)granathylakoidand(2)intergranalthyalkoids.
Thethylakoidsineachgranumarecontinuouswiththoseinothergrana
throughintergranalthylakoids.
Inthechloroplastthethylakoidsareembedded,orsuspended,inamatrix,
thestroma,whichhasasomewhatgranularappearance.

27. Types of Plastids

28. Functionsofplastids:
Leucoplastsaremainlyconcernedwithstorageofvariouskindsofreservefood
materials.
Chromoplastsmakeflowersandfruitsshowyandattractive.Theflowers
attractinsectsandotheranimals,whichhelpinpollinationanddispersalof
fruitsandseeds.
Chloroplastsarespecializedforphotosynthesis,thebiologicalconversionof
lightenergyabsorbedbychlorophylls,thegreenleafpigments,intopotential
chemicalenergysuchascarbohydrates.

29. 11.Nucleus:
•Thenucleusisthemostprominentstructureofcell.
•Nucleusispresentonlyincellsofhigherplantsi.e.eukaryotes.
•Generallythereisasinglenucleuspresentineachcell,butthereare
exceptionsalsoinsomefungie.g.,Rhizopusetc.andalgae
e.g.,Vaucheriamorethanonenucleusarepresent.
•Nucleusisabsentinsimplerone-celledplants-prokaryotese.g.,Viruses,
bacteriaandcynobacteria.
•Thespherical-shapednucleus,consistsofasemifluidmatrixknownas
nucleoplasminwhichoneormorenucleoli,andchromatinthreadsare
suspended.
•Nucleuscontrolscellularmetabolismofcellsandcontainsallgenetic
informationandisabletotransmititfromonegenerationtotheother.
•Thenucleusisthemostprominentofcell.
•Thenucleiofcellconsistoffourcomponents:-
1.NuclearMembrane, 2.Nucleoplasm,
3.Nucleolus, 4.Chromatin.

31. 1.Nuclearmembrane:-
•Thenuclearmembraneisadouble-layeredmembranethatenclosesthe
nucleus,andseparatesthecontentsofthenucleusfromthecellular
cytoplasm.
•Thespacebetweenthelayersiscalledtheperinuclearspaceandconnected
withanetworkoftubulesandsacs,calledtheendoplasmicreticulum,where
proteinsynthesisoccurs.
•Themembraneisperforatedbynumerousporescallednuclearpores.These
poresregulatetheflowofmoleculesbetweenthenucleusandcytoplasm,
•Thenuclearmembraneissemi-permeable;permittingselectivemoleculesto
passthroughthemembrane,intoandoutofthenucleus.
•Theinnernuclearmembranehasaproteinliningcalledthenuclearlamina,
whichbindstochromatinandothernuclearcomponents.
•Thefunctionofthenuclearenvelopeistoconfinethematerialsnecessaryfor
DNAandRNAsynthesisinsidethenucleus,andcontrollingmovementinto
andoutofthenucleus.

32. 2.Nucleoplasm:-
•Thenucleoplasmissemifluid,granularsubstanceormatrixthatfillsthe
interiorofthenucleus.
•Thenucleolusandthechromatinnetworkliesuspendedinthenucleoplasm.
•Nucleoplasmisdistinctfromcytoplasmduetothehighconcentrationof
materialslikenucleotides,whichareusedtomakeDNAandRNA,andthe
suiteofenzymeswhichcontroltheDNAandRNAconstructionreactions.
3.Nucleolus:-
•Thenucleuscontainsonetofourdenselygranularregioncallednucleoli
(singlur"nucleolus"),butwithineachspeciesthenumberofnucleoliisfixed.
•Thereisnomembraneseparatingthenucleolusfromtherestofthenucleus.
•Thenucleolus,whichisimportantintheformationofribosomes,appearsasa
densemassofRNA(ribonucleicacid),ribosomalRNA,chromatin,and
proteins.
•Whenacellreproducesthenucleolusdisappearsandreappearaftercell
formation.

33. Thenucleolusiscomposedoffourregions:-
a.Granularregions:containsribonucleoproteinsgranules
b.Fibrillarregions:containsribonucleoproteinsfibrils
c.Amorphousregions:Containsamorphousproteinthathydrolyzethepepsin.
d.Chromatinfibrils:Perinuclearchromatinandintranuclearchromatinarealso
associatedwithnucleolus.
4.ChromatinandChromosomes:-
•Thenucleuscontainsthecomplexofdeoxyribonucleicacid(DNA)and
associatedproteins,knownaschromatinintheuncondensedstateandas
chromosomesinthecondensedstate.
•Thechromatinisembeddedinaclearmatrixcalledthenucleoplasm.
•ChromatinarecoiledstrandsofDNAthatarefoundspreadthroughoutthe
nucleus,thatcometogetherandcoiltightlyduringcellreplication.
•EachDNAstrandwrapsaroundgroupsofsmallproteinmoleculescalled
histones,formingaseriesofbead-likestructures,callednucleosomes,
connectedbytheDNAstrand.
•Histonesarefoundonlyinnucleusandbeingbasicproteininteractstrongly
withdeoxyribonucleicacid(DNA).
•Thehistoneproteinsarerichinlysineandarginine.

34. 12.Cytoskeleton:-
•Acomplexnetworkoffibrousstructuresinthecytoplasmiscalled
cytoskeleton.Theyextendthroughoutthecytoplasmandmaintaintheshape
ofcells.Theyareconcernedwithstructuralframe-workanddirectlyinvolved
inmovementofcells.Theyalsoprovidethemachineryforthecyclosisin
cytoplasm.Twoprimarykindsofcytoskeletonareasfollows:
a.Microfilaments:arelong,thin,veryfinefilamentofproteinactin.Itplays
majorroleincyclosisandamoeboidmotion.Theyalsohelpinmuscle
contarctuinaswellashelpincellmigrationduringembryonicdevelopment.
b.Microtubules:arelong,hollow,cylindrical,unbranched,tubules.Itsmajor
roleistomakestructuralframe-workofcellandmaintaintheshapeofthe
cell.Theyalsohelpinintracellulartransportofmaterials.
13.CytoplasmicInclusions(ErgasticSubstances):-
•Asaresultofmetabolicactivitiesseveralkindsofnon-livingsubstancesare
producedwithinthecell,whicharecalledcytoplasmicinclusionsorergastic
substances.Theymaybeinsolution,colloidalorsolidcrystalform.

35. Basically,theseareclassifiedintothreetypes:
1.ReserveMaterials:Sugars,starch,Inulin,Pectin,Cellulose,Glycogen,
Nitrogenousmatters,Fatsandoils.
2.ExcretoryMaterials:Tannins,Resins,Latex,Gums,Alkaloids,etc
3.SecretoryMaterials:Nectar,Anthocyaninsandanthoxanthins,Hormones