ALL IB Biology Essay Questions

IBBiologyHLEssayQuestions UNIT 1: CELL BIOLOGY 31.1:INTRODUCTIONTOCELLS 31.2:ULTRASTRUCTUREOF CELLS 41.3:MEMBRANE STRUCTURE 61.4:MEMBRANE TRANSPORT 71.6:CELL DIVISION 8 UNIT 2:MOLECULAR BIOLOGY 92.1:MOLECULES TO METABOLISM 92.2:WATER 102.3:CARBOHYDRATES ANDLIPIDS 102.4:PROTEINS 112.5:ENZYMES 122.6:STRUCTUREOF DNAAND RNA 122.8:CELL RESPIRATION 142.9:PHOTOSYNTHESIS 14 UNIT 3:GENETICS 163.1:GENES 163.2:CHROMOSOMES 163.3:MEIOSIS 173.4:INHERITANCE 17 UNIT 4:ECOLOGY 194.1:SPECIES , COMMUNITIES ANDECOSYSTEMS 194.2:ENERGY FLOW 194.3:CARBON CYCLING 204.4:GREENHOUSEEFFECT 20 UNIT 5:EVOLUTIONAND BIODIVERSITY 215.1:EVIDENCEFOREVOLUTION 214.2:NATURAL SELECTION 225.3:CLASSIFICATIONOF BIODIVERSITY 23 UNIT 6:HUMAN PHYSIOLOGY 266.1:STRUCTUREOF THE DIGESTIVE SYSTEM 266.2:THE BLOOD SYSTEM 286.3:DEFENSE AGAINST INFECTIOUS DISEASES 306.5:NEURONS AND SYNAPSES 326.6:HORMONES , HOMEOSTASIS AND REPRODUCTION 35 UNIT 7:NUCLEIC ACIDS 377.1DNASTRUCTUREAND REPLICATION 377.1:TRANSCRIPTIONAND GENE EXPRESSION 397.3:TRANSLATION 39 UNIT 8:METABOLISM , CELLRESPIRATIONANDPHOTOSYNTHESIS 41

8.1:METABOLISM 418.2:CELL RESPIRATION 428.3:PHOTOSYNTHESIS 45 UNIT 9:PLANT BIOLOGY 499.1:TRANSPORTINTHE XYLEMOF PLANTS 499.2:TRANSPORTINTHE PHLOEMOF PLANTS 529.3:GROWTHIN PLANTS 529.4:REPRODUCTIONIN PLANTS 52 UNIT 10:GENETICS AND EVOLUTION 5410.1:MEIOSIS 5410.2:INHERITANCE 5510.3:GENEPOOLS ANDSPECIATION 56 UNIT 11:ANIMAL PHYSIOLOGY 5811.1:ANTIBODY PRODUCTIONAND VACCINATION 5811.2:MOVEMENT 6011.3:THE KIDNEYAND OSMOREGULATION 6211.4:SEXUAL REPRODUCTION 63 Notes: 2

Unit1:CellBiology 1.1:Introductiontocells 1. Discusspossibleexceptionstocelltheory. 4marks ▪ skeletalmusclefibersarelarger/havemanynuclei/arenottypicalcells▪ fungalhyphaeare(sometimes)notdividedupintoindividualcells▪ unicellularorganismscanbeconsideredacellular▪ becausetheyarelargerthanatypicalcell/carryoutallfunctionsoflife▪ sometissues/organscontainlargeamountsofextracellularmaterial▪ e.g. vitreoushumorofeye/mineraldepositsinbone/xylemintrees/otherexample▪ statementofcelltheory/alllivingthings/mosttissuesarecomposedentirelyoftruecells 2. Eukaryoticcellshaveintracellularandextracellularcomponents.Statethefunctionsofonenamedextracellularcomponent. 4marks nameofcomponent:1max ▪ e.g.plantcellwall/cellulose/interstitial▪ matrix/basementmembrane/glycoprotein/bonematrix; functions:3max EITHER ▪ e.g.(plantcellwall)strengthens/supportsthecell/plant(againstgravity);▪ preventstheentryofpathogens;▪ maintainstheshapeofplantcells;▪ allowsturgorpressure/highpressuretodevelopinsidethecell;▪ preventsexcessiveentryofwatertothecell; OR ▪ helpscellstosticktogether/adhere;▪ neededtoholdcells/tissuestogether/exampleofcells/tissuesholdingtogether;▪ formsinterstitialmatrix/formsbasementmembranetosupportsinglelayersofcells;▪ e.g.aroundabloodcapillary;▪ forms(partofthe)filtrationmembraneintheglomerulus; 3. Explainhowthesurfacearetovolumeratioinfluencescellsizes. 3marks ▪ smallcellshavelargerratio(thanlargercells)/ratiodecreasesassizeincreases▪ surfacearea/membranemustbelargeenoughtoabsorbnutrients/oxygen/substancesneeded▪ surfacearea/membranemustbelargeenoughtoexcrete/passoutwasteproducts▪ needformaterialsisdeterminedby(cell)volume▪ cellsizeislimited(bySA/Volumeratio)/cellsdividewhentheyreachacertainsize▪ referencetodiffusionacross/throughmembrane/surfacearea 4. Outlinedifferentiationofcellsinamulticellularorganism. 4marks ▪ differentiationisdevelopmentindifferent/specificways▪ cellscarryoutspecializedfunctions/becomespecialized 3

▪ exampleofadifferentiatedcellinamulticellularorganism▪ cellshaveallgenes/coulddevelopinanyway▪ somegenesareswitchedon/expressedbutnotothers▪ position/hormones/cell-to-cellsignals/chemicalsdeterminehowacelldevelops▪ agroupofdifferentiatedcellsisatissue 5. Describetheimportanceofstemcellsindifferentiation. 3marks ▪ stemcellsareundifferentiatedcells;▪ embryocellsarestemcells;▪ stemcellscandifferentiateinmany/allways/arepluripotent/totipotent;▪ differentiationinvolvesexpressingsomegenesbutnotothers;▪ stemcellscanbeusedtorepair/replacetissues/healwounds; 1.2:UltrastructureofCells 6. DrawalabeleddiagramtoshowtheultrastructureofEscherichiacoli. 6marks Award1foreachstructureclearlydrawnandcorrectlylabeled. ▪ cellwall–withsomethickness;▪ plasmamembrane–shownassinglelineorverythin;▪ cytoplasm;▪ pilus/pili–shownassinglelines;▪ flagellum/flagella–shownasthickerandlongerstructuresthanpiliandembeddedincellwall;▪ 70Sribosomes;▪ nucleoid/nakedDNA;▪ approximatewidth0.5μ m/approximatelength2.0μ m; Award4maxifthebacteriumdrawndoesnothavetheshapeofabacillum(rounded-cornerrectanglewithlengthapproximatelytwiceitswidth). Award4maxifanyeukaryoticstructuresincluded. 7. Drawalabelleddiagramtoshowtheorganelleswhicharefoundinthecytoplasmofplantcells. 6marks ▪ roughendoplasmicreticulum▪ freeribosomes▪ Golgiapparatus▪ mitochondrion▪ chloroplast▪ vacuole▪ nucleus▪ lysosome▪ smoothendoplasmicreticulum 4

8. Drawalabelleddiagramshowingtheultra-structureofalivercell. 4marks Award1foreachstructureclearlydrawnandcorrectlylabelled.Wholecellsnotnecessary. ▪ (plasma)membrane–singlelinesurroundingcytoplasm;▪ nucleus–withadoublemembraneandpore(s)shown;▪ mitochondria(ion)–withadoublemembrane,theinneronefoldedintointernal▪ projections,shownnolargerthanhalfthenucleus;▪ roughendoplasmicreticulum–multi-foldedmembranewithdots/smallcirclesonsurface;▪ Golgiapparatus–shownasaseriesofenclosedsacswithevidenceofvesicleformation;▪ ribosomes–dots/smallcirclesincytoplasm/ribosomesonrER;▪ lysosome; Award0ifplantcellisdrawn.Award2maxifanyplantcellstructure(e.g.cellwall)ispresent. 9. Stateonefunctionofeachofthefollowingorganelles:lysosome,Golgiapparatus,roughendoplasmicreticulum,nucleus,mitochondrion. 5marks ▪ lysosome:hydrolysis/digestion/breakdownofmaterials(macromolecules)▪ Golgiapparatus:synthesis/sorting/transporting/secretionofcellproducts▪ roughendoplasmicreticulum:siteofsynthesisofproteins(tobesecreted)/intracellulartransportofpolypeptidestoGolgiapparatus▪ nucleus:controlscellsactivities/mitosis/replicationofDNA/transcriptionofDNA(toRNA)/directsproteinsynthesis▪ mitochondrion:(aerobic)respiration/generatesATP 5

10.Distinguishbetweenthestructureofplantandanimalcells. 6marks Award1markperdifference plantcells ▪ havecellwalls,animalsdonot▪ haveplastids/chloroplasts,animalsdonot▪ havealargecentralvacuole,animalsdonot▪ storestarch,animalcellsstoreglycogen▪ haveplasmodesmata,animalcellsdonot▪ fixedshape/moreregularshape animalcells ▪ havecentrioles,plantcellsdonot▪ havecholesterolinthecellmembrane,plantcellsdonot▪ morerounded 11.Usingatable,comparethestructuresofprokaryoticandeukaryoticcells. 5marks ProkaryoticCells EukaryoticCellsNaked/loopofDNA DNAassociatedwithprotein/histones/nucleosomes/DNAinchromosomesDNAlocatedincytoplasm/nucleoid/nonucleus DNAlocatedwithinanucleus/nuclearmembraneMembraneboundorganellesabsent Membraneboundorganellespresent70SRibosomes 80SRibosomesSameplasmamembranestructureasEukaryoticcells SameplasmamembranestructureasProkaryoticcellsCellwalliscomposedofpeptidoglycan/notcomposedofcellulose/notcomposedofchitin Cellwalliscomposedofcellulose/chitin/notcomposedofpeptidoglycan Mitochondriaabsent MitochondriapresentPilipresent PiliabsentPlasmids(sometimes)present PlasmidsabsentFlagellasolid Flagellaflexible/membrane-bound 1.3:MembraneStructure 12.Drawadiagramtoshowthestructureofacellmembrane 5marks ▪ phospholipidslabelledwithhydrophillic(heads)andhydrophobic(tails)▪ phospholipidbilayerclearlyshownandlabelled▪ proteinsshowninthebilayerandlabelled▪ transmembraneandperipheral/extrinsicproteinsshownandlabelled▪ glycoproteinsshownandlabelled▪ cholesterolshownandlabelled▪ glycolipidsshownandlabelled▪ thicknessshownas10nm/+or-2nm 6

13.Explainhowthestructureandpropertiesofphospholipidshelptomaintainthestructureofcellmembranes. 9marks phospholipidstructure ▪ hydrophobictail/hydrophilichead▪ headmadefromglycerolandphosphate▪ tailmadefromtwofattyacids▪ saturated/unsaturatedfattyacid(intail) arrangementinmembrane ▪ phospholipidsformabilayer▪ headsfaceoutsidethemembrane/tailsfaceins