RevisionPackBIOLOGY

CB1OverarchingThemesinBiology

CB2CellsandControlCB3Genetics

CB4NaturalSelection&GeneticModification

_____________________________________________________

“When we tackle obstacles, we find hidden reserves of courage and resilience we did not know that we had.”

-A.P.K Abdul Kalam

“Be kind, for everyone you meet is fighting a battle.” –Plato

“Just be yourself man, be proud of who you are.” –Eminem

CB1OverarchingThemesinBiologyLightmicroscopesareusedtoseesmallobjectssuchascellsTheyuselightandlensestomagnifyimagesThistriangleisusedtocalculatethesizeofasamplefromimagesizeandmagnification.Electronmicroscopesaremorepowerful,anduseelectronbeamstoseeevensmallerobjects.Thesamplemusthoweverbedead,andtheimagesarealwaysinblackandwhiteAsthingsaresosmall,wesometimesusestandardformtomeasurethem.Forexample,acellwouldbemeasuredinmicrometres(1x10-6m)Thesub-cellularstructuresinacellarecalledorganellesAcellwithanucleusiscalledaeukaryote(i.e.aplant/animalcell)Acellwithoutanucleusiscalledaprokaryote(i.e.abacteria)Thediagramsbelowshowwhichorganellesarefoundineachcelltype.Specialisedcellshaveadifferentshape/adaptationastheyhaveaspecificfunctionExamplesaregivenbelow:

Cell Adaptation Function

Sperm(animalcell)

Haploid(halftheDNA)AcrosomefullofenzymesTailLotsofmitochondria

TofusewiththeovumnucleusTobreakthroughtheovumcellmembraneToswimtotheovumToproducelotsofenergyforswimming

Ovum(animalcell)

Haploid(halftheDNA)Fullofnutrients

TofusewiththeovumnucleusTohelpdevelopthefoetus

CiliatedEpithelial(animalcell)

Smallcilia(hairs) Tobrushawaymucusfullofbacteria

Nerve(animalcel)

LongaxonMyelinatedsheathManydendrites

TocarryelectricalsignalslongdistancesTospeedupthenervesignal(insulator)Toreachothernervecells

Redbloodcell(animalcell)

NonucleusDiscshaped

Moreroomforhaemoglobin(tocarryoxygen)Largersurfaceareatodiffusegases

Roothaircell(plantcell) Largesurfacearea Toabsorbmorewater

Palisadecell(plantcell)

Lotsofchloroplasts Toabsorbsunlightforphotosynthesis

Enzymesarebiologicalcatalyststhatspeedupchemicalreactionsinsidelivingthings.Theyareproteins.Enzymeseitherbreakdownlargemoleculesorputsmallermoleculestogethertomakelongerones.Enzymeshaveaspecificactivesitethatonlymatchesonesubstrate.Whentheenzymeisbondedtoitssubstrate,itiscalledan‘enzyme-substratecomplex’Ifanenzymegetstoohot/acidic/alkaline,itwillchangeshapeandstopworking(denature).Increasingtheamountofsubstratecanincreasetherateofenzymeaction.Commonenzymesinvolvedindigestionare;Lipase;LipidsàfattyacidsProtease;ProteinsàaminoacidsAmylase;StarchàglucoseDiffusionisthemovementofparticlesfromahighconcentrationtoalowconcentrationOsmosisisthemovementofwaterfromahighconcentrationofwatertoalowconcentrationofwaterthroughasemi-permeablemembraneThisishowwatergetsintoredbloodcells,roothaircellsandwhysweetsswellinaglassofwaterDiffusionandosmosisarecalled‘passivetransport’becausetheydonotrequireenergy

DIFFUSION OSMOSIS

Ifyouplacepotatoinasolutionofconcentratedsugar,thatismoreconcentratedwithsugarthanthepotato,thewaterwillcomeoutofthepotatointothesolution.Thepotatowilldecreaseinmass.Ifyouplaceapotatoinpurewater,wherethereisalowerconcentrationofsugar,thewaterwillinsteadmoveintothepotatoanditwillincreaseinmass.Tocalculatethepercentagemasslost,youusethisequation;Finalmass–startingmassx100InitialmassActivetransportisthemovementofparticlesfromalowconcentrationtoahighconcentration;thisrequiresenergyandnormallyoccursthroughaspecialchannelinthemembrane.

CB2CellsandControlThecellcycleincludesthegrowthandreplicationoflivingcellsInterphase=cellgrowsandreplicatesMitosis=nucleussplitsintotwoCytokinesis=thecytoplasmsplitsintotwoCellsdomitosis/cellreplicationfor;growth,repair,reproduction(prokaryotes)andcanceroustumoursThestagesofmitosisare;Prophase–DNAorganisesintochromosomesMetaphase–chromosomeslinesupdownthecentreofthecellAnaphase–chromosomesgetpulledtoeithersideofthecellbyspindlesTelophase–newnuclearmembranesformaroundthechromosomesCytokinesis–cytoplasmsplitsintwotomaketwoidenticalcellsLivingorganismscangrowinthefollowingways;IncreasethesizeofcellsIncreasethenumberofcellsElongation–cellsgettinglongerDifferentiation–cellschangingtypeandspecialisingWemeasuretheexpectedgrowthofhumansonPercentileGrowthCharts,thatshowifapersonisfollowinganormalgrowthpattern.Italsohelpsustocomparetheirsize(massandheight)withthenationalaverage.Plantsalsogrowthroughcellelongation,differentiationandcelldivisionThemeristematthetipoftheshootandtherootisasiteofrapidreplicationanddifferentiationStemcellscandifferentiateintomanytypesofspecialisedcells.Embryonicstemcellscandifferentiateintoallcelltypesofthatspecies,whilstadultstemcellscanonlydifferentiateintoalimitednumberofcelltypes.Stemcellscanalsobefoundintheumbilicalcord.Thereislotsofpotentialforstemcellstobeusedinmedicine,repairingtissuesandorgans.Somepeoplethinkitiswrongtoproduceembryosforstemcellresearch,andintheUKweonlyuseun-implantedembryosoriginallydevelopedforIVFforresearch.

Nerves(neurones)carryelectricalsignalsaroundthebody.Therearethreemaintypesdescribedbelow.

Thesethreeneuronetypessometimesworkwithoutthebrain.Thisiscalledareflexandismuchquickerthanreactionsthatinvolveyourbrain.Examplesincludeyourpupildilatingindimlight,oryourhandquicklymovingawayfromahotsurface

Synapsesarethegapsbetweennerves,wheretheymeeteachother.Chemicalscalledneurotransmitterspassoverthesegapsto

startanelectricalsignalinthenextnerve. Somedrugscausemore/lessneurotransmittertobereleased,thereforethey

speeduporslowdownreactionsinthenervoussystem.

Thestructureofeachnerve(neurone)helpsthebodycarryelectricalsignalsaroundthebodyquickly.Theyhaveamyelinsheathtospeeduptheimpulse,alongaxontocarrythesignal

longdistance,anddendritestoreachothernervecells.QUESTIONS TO TEST YOURSELF – CB1 & CB2

1. Whatorganellesareonlyfoundinaplantcell?2. Whichtypeofmicroscopeismorepowerful?3. Whatisthedifferencebetweenaeukaryoteandaprokaryote?4. Whatdoesacellwalldo?5. Whatistheacrosomeinaspermcell?6. Whatistheadaptationofaroothaircell?7. Whydoenzymesonlyworkononesubstrate?8. Whathappenstoanenzymeinanalkalisolution?9. Whatdoes‘denature’mean?10. Whathappenstoapotatocubeinpurewater?Why?11. Doesdiffusionrequireenergy?12. Howdoyoucalculatepercentagemassloss?13. Whyareembryonicstemcellsmoreusefulthanadultstemcells?14. Whatdoes‘differentiate’mean?15. Wheredoyoufindarelayneurone?

Neuronetype Location FunctionSensoryneurone Fromsenseorganàrelayneurone TosensethingsRelayneurone Fromsensoryneuroneàmotorneurone

OftenfoundinthespinalcordTopassonmessagestothemotorneuroneorthebrain

Motorneurone Fromrelayneuroneàmuscles(effectors) Tomakeusreacttoastimulus

CB3GeneticsMeiosisistheproductionofgametes(spermorovum)fromadiploid(twocopiesofeachchromosome)cell.Meiosisproduces4daughtercellsthatarehaploid(containsonecopyofeachchromosome).Allthehaploiddaughtercellsaregeneticallydifferent,soalloffspringaregeneticallydifferent.The‘genome’istheentireDNAofanorganism.A‘gene’isasmallsectionofDNAthatcodesforaprotein.DNAisapolymer,madeupof4bases;A,C,G,TThestrandofDNAcoilsintoadouble-helixshape,ascomplimentarybasesbondtogetherwithweakhydrogenbonds.AbondstoT,CbondstoG.Analleleisadifferentversionofthesamegene.Forexampleblueeyedandthebrowneyedarebothallelesoftheeyecolourgene.Everypersonhastwocopiesofeachgene;onefromtheirMotherandonefromtheirFather.Ifbothcopiesarethesameallele,itiscalledhomozygous.Twodifferentallelesarecalledheterozygous.Adominantalleleisexpressedinthephenotype(physicalattribute)Arecessivealleleisonlyexpressedisbothcopiesarerecessive.Genotypes:H=dominanth=recessive HH=homozygousdominant Hh=heterozygoushh=homozygousrecessiveIfyouknowthegenotype(whichalleles)ofthemotherandfather,youcancalculatethechanceoftheiroffspring’sDNA.APunnettsquareisusedtocalculatethisasseenabove.Ageneticdiagramlikethiscanalsobeusedtocalculatethechancesofoffspringbeingmaleorfemale.Mostphenotypes(physicalattributes)aretheresultofmultiplegenesworkingtogether,insteadofjustonegene.Differenceswithinaspeciesiscalledvariation.Variationiscausedbygenesfromsexualreproduction,environmentalfactorsandgeneticmutations.

CB4NaturalSelection&GeneticModificationTheprimarysourceofevidenceforhumanEvolutionisfossils.Famousfossilsinclude:Ardi–4.4mya(millionyearsago)Lucy–3.2myaLeakey’sdiscoveryoffossilsfrom1.6myaThediscoveryofstonetoolsalsoshowshowspeciespriortohumansbegantoformandusetoolstoaidsurvival.Thisisconsideredanimportantstepinourevolutionaryhistory.Darwindevelopedthetheoryofnaturalselection,afterobservinghowpopulationschangedovertime.

1. Thereisvariationwithinaspecies2. Someofthesevariationsarebeneficial3. Livingorganismswiththebeneficialmutationaremorelikelytosurviveandreproduce4. Thebeneficialvariationispassedongeneticallytothenextgeneration5. Lessbeneficialmutationsarenotpassedon6. Overmanygenerations,thespecieschangestobeincreasinglywelladadpted

Forexample:1. Somegiraffeshaveshortnecks.Byageneticmutation,somehavelongernecks2. Havingalongerneckismoreusefulforobtainingfood3. Thegiraffesthatcanreachmorefoodwillmorelikelysurviveandreproduce4. Thegeneticmutationforalongerneckwillbepassedon5. Theshorterneckgeneisnotpassedonasmuch6. Overtime,moregiraffeshavelongernecks–thespecieshaschangedovertime7.

Wecanseethishappeningtodaywiththeincreaseinantibiotic-resistantbacteria.Thebacteriathatareresistanttoantibioticsaresurvivingandreplicatingmoresuccessfully–changingthespeciesovertime.Otherevidenceforthistheoryofevolutionisthepentadactyllimb–manyspeciesthatallseemtohaveafive-digitlimb,Thissuggestsweallshareacommonancestor,buthaveadaptedovertimetomatchenvironments,locomotionandlifestyle.Livingthingsusedtobeclassifiedinto5kingdoms,basedontheircellularstructure.However,geneticanalysisshoweddistinctdifferencesintheDNAofsomeprokaryotes,solivingthingsarenowclassifiedinto3domains,basedonthisgeneticanalysis.

1. Archaea–Prokaryotes2. Bacteria–Prokaryotes3. Eukaryotes;includingFunghi,PlantaeandAnimalia

Selectivebreedingisamethodofpurposefullyreproducingorganismswithdesiredtraits,toincreasethechanceofpassingondesiredgenestotheiroffspring.Forexample,breedingtwocowswithlargemusclemasstoproducecattleforbeef.Thisprocessisrepeatedovermanygenerationstoincreasinglyproducethe‘best’changeovertime.Geneticengineeringhowever,involvesthedirectmanipulationofDNAinthenucleus,forexample:

1. Tomakecropsresistanttoherbicides,2. ToincreasetheamountofVitaminAinrice(goldenrice)3. Toincreasethesizeoffruit/vegetables

Bacteriaplasmidsareoftenusedforthis,asrestrictionenzymescancutasmallsectionofDNAoutoftheplasmid,andreplaceitwiththedesiredgene.Thisishowhumaninsulinisnowmanufacturedfordiabetics.

QUESTIONS TO TEST YOURSELF – CB3 & CB4

1. Whatdoes‘diploid’mean?2. Howmanycellsareproducedinmeiosis?3. Howisa‘gene’differenttoa‘genome’?4. Whatarethe4basesofDNA?5. WhichbasepairswithA?6. Howwouldyoudescribethegenotype‘HH’?7. Whatisaphenotype?8. WhendoscientiststhinkArdiwasalive?9. Giveanexampleofaspecieschangingbecauseofnaturalselection.10. Howhaveantibioticresistantbacteriadeveloped?11. Whatisthepentadactyllimb?12. Whatarethe3domains?13. HowhaveweusedGeneticEngineeringtohelppeople?