y3 cells

Cells Thecellisthebasicunitoflife.Differentcellshavedifferentfunctions. Cell membrane● Separatesandprotectsacellfromitssurroundingenvironment.● Partiallypermeableandcontrolshowsubstancesmoveinandoutofthecell.Fluidmosaicmodelisusedtodescribethestructureofthecellmembrane.Thecellmembraneisalwaysmoving.Thecellmembraneisfluidinthatphospholipidsandproteinsarenotstationary,butcanmoverapidlyacrossthesurfaceofthemembrane.Thecellmembraneisamosaicinthatmanydifferentproteinmoleculesarerandomlyscatteredandembeddedthroughoutthephospholipidlayer.Duetothenatureofthephospholipids,onlysmallhydrophobicmoleculescanpassthroughthephospholipidbilayer. Hence,transportproteinsarerequiredforhydrophilicorwatersolublemoleculestopassthroughthephospholipidbilayer. CytoplasmThecomponentsofthecytoplasminclude:1) CytosolAqueoussolutionofessentialions,solubleproteinssuchasenzymeandsolubleorganiccompoundssuchassugarsoraminoacids2) CytoskeletonNetworkofproteinfibresthatgivesupport,mobilityandregulationtothecell3) Organelles Cell wallOnlyfoundinplantcells,fungiandbacteriaItisfullypermeableMadeofcellulose(Apolymer. Monomerisglucose)Function:-Toprovidemechanicalsupportforplantcellsandtotheplant,especiallyforplantswithsoftstems.-Toresistexpansionwhenwaterentersbyosmosis,ensuringintegrityofplantcellandtoprovideturgidity

Membranouscell organelles NucleusThenucleusisthelargestorganellewithintheeukaryoticcell.Itconsistsofa nuclearenvelopewhichseparatesthenucleusfromthecytoplasm.Italsocontainsthenucleoluswhichsynthesisesribosomes.ItcontainsDNA.Thenucleusisfoundinalmostalleukaryoticcells,exceptformaturatedbloodcells. Function:Containsthehereditarymaterial(DNA)andcontrolsactivitiesofthecell Endoplasmicreticulum Roughendoplasmicreticulum(RER) Asystemofflattenedmembrane-boundsacs.Itappearsroughundertheelectronmicroscopeduetothepresenceofribosomesonitssurface. ModifiesproteinsmadebyboundribosomesandtransportsthemtoGolgiapparatusviatransportvesicles Smoothendoplasmicreticulum(SER) Consistsoffinetubules Lipidsynthesis,detoxificationofdrugsandpoisonsStorageandreleaseofcalciumions Golgi apparatusNote:The¨Golgi¨mustbeacapitalGTheGolgiapparatusconsistsofstacksofflattenedmembraneboundsacs. Function:TheGolgiapparatuschemicallymodifiestheproductsitreceivesfromtheendoplasmicreticulumandpackagesthembeforesendingthemtodestinationsinsideoroutofthecellduringvesicles. LysosomesLysosomesaresmall,sphericalvesiclesthataresurroundedbyasinglemembrane.Lysosomescontainhydrolyticenzymessuchaslipases,proteasesandnucleases.

Function:Todigestmaterialsmadeinthecellortakeninfromoutsidebyphagocytosis,ortodigestworn-outorganellesinthecell.Thisprocessisknownasautophagy Vacuoles Animal Fluid-filledsacboundbyasinglemembrane.Formedeitherbythepinching-off partofthecellmembrane,orbyenlargementofavesiclefromtheGolgiapparatus.Itisusuallyrelativelysmallerascomparedtotheplantvacuole,andexiststemporarily. Foodvacuolesareformedbyphagocytosis(eg.Inthecaseofintracellulardigestionbymacrophages) Plant Verybig,central,surroundedbymembranes.Itoccupiesover80%ofthecellvolume.Itisenclosedbyasingle,partiallypermeablemembraneknownasthetonoplast.Thevacuoleisfilledwithcellsap,asolutionmadeupofsugars,ions,wasteproductsandpigments. Storagesitefornutrientsuchasproteinstorageinseedandinorganicionseg.K ⁺ andCl ⁻Thevacuoleisalsoadisposalsiteformetabolicby-productsthatwouldendangerthecelliftheyremainedinthecytosol.Maycontaincolourpigments MitochondriaMitochondria(plural)Mitochondrion(singular)Themitochondriaisrod-shapedorcylindrical.Itisboundedbyadoublemembranewhichprovidesincreasedsurfaceareaforchemicalreactionstotakeplace. Function:Mitochondriaisinvolvedinaerobicrespiration.Releaseofenergyintheformofadenosinetriphosphate(ATP)molecules.ATPistheenergyusedbyalllivingthings.Cellswhichrequireaconstantsupplyofenergywouldcontainalargenumberofmitochondria,suchasliverandmusclecells.Donotwrite¨produce¨energyasitimpliesthatenergycanbecreatedordestroyed.Energycannotbecreatedordestroyed.

ChloroplastsChloroplastsareboundedbyadoublemembrane.Itcontainschlorophyllandcontainsthylakoidsandstoma.Function:Siteofphotosynthesis Non-membranousorganelles RibosomesRibosomesaresmallroundstructuresfoundinallcells.Theymayoccurasfreeribosomessuspendedinthecytosolorboundtoroughendoplasmicreticulum. Function:Ribosomesarethesitesofpolypeptidesynthesis.Freeribosomesgenerallymakeproteinsthatwillfunctionwithinthecytosol.Boundribosomesgenerallymakeproteinsthataredestinedforinsertionintomembranes,forpackagingwithincertainorganellessuchaslysosomesorforexportfromthecell. CentriolesCentriolesaresmallhollowcylinderswhichoccurinpairs.Theyarefoundinanimalcells,butabsentinplantcells.Function:Playaroleincelldivisioninanimalcells Processesinacell necessaryfor life ProteinSynthesisPolypeptidechainsaresynthesisedattheribosomesandfoldedattheroughendoplasmicreticulum.Transportvesiclescontainingsubstancesmadebytheendoplasmicreticulumpinchedoff fromtheER.ThesetransportvesiclesthenfuseandreleasetheirsubstancesintotheGolgiapparatuswheretheyarechemicallymodifiedandpackaged.Secretoryvesiclescontainingthesemodifiedsubstancesarepinchedoff fromtheGolgiapparatus.Thesecretoryvesiclesmovetowardsandfusewiththecellmembrane,releasingthesubstancesoutsidethecellbyexocytosis.rd

Formationof lysosomeEnzymecontentsaresynthesisedontheroughendoplasmicreticulumandtransportedviatransportvesiclestotheGolgiapparatusforfurtherprocessing.Avesiclecontainingtheprocessedenzymesbudsoff fromtheGolgiapparatus,formingalysosome.Theenzymeshavetobekeptapartfromtherestofthecell,orelsetheywoulddestroythecell. Divisionof labourDivisionoflabouristhesharingofdifferentfunctionsinanorganismamongitscells,tissues,organsandsystems.Italsoensuressmoothrunningandeffectiveworkingofthedifferentpartsinanorganismaswellastheorganismasawhole.Disadvantagesofdivisionoflabour:Ifonepartofthesystembreaksdown,theentiresystemmightbeunabletofunctionsmoothly.