2020 TYS Answers (ThatBioTutor)

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) TYSAnswers2020(ThatBioTutorEdition) IMPTNOTE:- Fordifferencesbetween2023and2024syllabus,seethislisthere.- *Shadedblack=outofsyllabusfrom2024onwards Question Ans Question Ans1* D 21 C2 B 22* D3 B 23 B4 D 24 A5 C 25 D6 A 26* B7 C 27 B8 A 28 A9 B 29 C10 D 30 D11 C 31 D12 B 32 D13 A 33* A14 C 34 C15 A 35 B16 A 36 C17* D 37 B18 B 38 D19 D 39 A20 D 40 D Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q1. (a)● A:Ovary● B:Oviduct/Fallopiantube● C:Cervix (b) (c) Choose3:● Afterfertilisation,thezygoteismovedfromtheoviducttowardstheuterus,byperistalticactionoftheoviductwallsandthesweepingactionofcilia.● Meanwhile,thezygotedividesbymitosisintoanembryo,● Whichembedsitselfintotheuterineliningduringimplantation,whereitdevelopsintoafoetus,● Finger-likeprojectionscalledvilli,containingthebloodvesselsfromtheembryo,growintotheuterinelining,formingtheplacenta. (d)(i) ● Astheovumisnotmotile,thesweepingactionoftheciliamoveovumfromtheovarytowardstheuterus. (ii)● Respiratorysystem. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q2.(a)● D:DNAreplicationisoccurringinthenucleusduringinterphase,doublingtheamountofDNA● E:Cytokinesisoccurred,splittingtheparentcellintotwodaughtercells,hencehalvingtheamountofDNApercell. (b)(i) ● Anaphase (ii)● Before:Metaphase● After:Telophase (iii)● Haploidnumber=3 ● Inthisstageofanaphase,thereare12daughterchromosomesintotal.Aftertelophaseandcytokinesis,therewillbe6chromosomesineachdaughtercell.● Sincemitosisoccursindiploidcells,andpreservesthechromosomenumberoftheoriginalparentcell,theoriginalcellhadsixchromosomes.● Haploidnumberwouldbehalfofthediploidnumber=6x0.5=3. (c)● DuetoindependentassortmentofchromosomesduringMetaphaseI,maternalandpaternalchromosomescouldbesegregatedintoeitherdaughtercellindifferentcombinations.● DuringProphaseI,crossingovermayoccur, resultinginnewcombinationsofallelesandformingchiasmata,increasingthegeneticvariationofthegametes.● Randomfertilisationofarandomspermandeggfurtherincreasesthegeneticvariationofthezygoteformed,increasingthenumberofoffspringvariants. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q3.(a) (b)● Codominance:Whenthetwodifferentallelesforatraitarebothexpressedandinfluencephenotype,suchastheI A andI B allelebothbeingexpressedhencetypeABredbloodcellshaveboththeAantigenandBantigenontheirplasmamembranes.● Multiplealleles:Whenmorethantwoallelesexistforacertaintrait,suchasthepresenceofI A I B I O alleles,whichareresponsibleforbloodgroupsA,BandOrespectively. (c)● Discontinuousvariationiswhentherearefewanddistinctphenotypes,suchasthe4bloodgroupsA,B,AB,O,andphenotypesarenotaffectedbytheenvironment. (d)● AgeneisasequenceofDNAnucleotidesthatcodesforaspecificpolypeptide,whileanalleleisanalternativeformofagene.● Individualsofthesamespecieshavethesamegenes,buttheymayhavedifferentalleles. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q4. (a)● Astheagemenstartedsmokingtabaccoincreasedfrom10-14to20-24yearsold,therelativedeathratedecreasedgraduallyfrom2to1.7,● Thendecreasedsharplyto1.25auat25-29yearsold.● Allsmokersinthestudyhadahigherdeathratecomparedtonon-smokerswhichisat1au. (b)● Occlusionofcoronaryarteriesduetoatherosclerosisnarrowsthelumen,reducingbloodflowtothecardiacmuscles.● Theheartmuscleslackoxygenandnutrientsforthemtoreleaseenergyviaaerobicrespiration,theymaystartdying,whichcanresultinchestpain.● Ifthefattydepositrupturesintheartery,abloodclotthatformsmaygetstuckandcompletelyblockthealreadynarrowedlumen,whichwouldthenleadtoaheartattack. (c)● Cigarettesmokecontainscarbonmonoxide,whichbindsirreversiblytothefoetus’haemoglobin,● suchthatitcannottransportoxygenanymore,reducingtheabilityofbloodtotransportoxygen.● Foetalcellsaredeprivedofoxygen,lessaerobicrespirationoccurstoreleaseenergyformitosisandmetabolicreactions,● Hencethefoetusgrowsslowerthanitshouldduringpregnancy,resultinginahigherchanceofhavinglowbodymasswhenborn. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q5.(a)● 40.00/0.04=1000 (b)● Astheinsecticideisnoteasilyexcretedfromorganisms’bodies,itaccumulatesinthemviabioaccumulation.● Eachsmallfishfeedsonmanywaterplants,largeamountsofinsecticideentersthem,biomagnificationhasoccurred.● Theprocessrepeatsupthefoodchain,hencethetopconsumer,fish-eatingbirds,hasthehighestconcentrationofitintheirbodies,andgetthemostpoisoned,henceahigherproportionofthemdiecomparedtothelowertrophiclevels. (c)● Ifallfish-eatingbirdsdie,therewillbenopredatortofeedonlargefishes,hencetheirpopulationwillincrease.● Thisresultsinmoresmallfishesbeingfedonbythelargefishes,● hencesmallfishpopulationwilldecreasesignificantly. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q6.(a)(i) ● Arteriesneedathickelasticlayertowithstandthehighpressureofbloodwithinthem,● Aswellastoeffectivelystretchandrecoilwithenoughforce,topushbloodforwardinspurts. (ii)● Themusclefibresallowfortheregulationofbloodflowtothetissuestheyareconnectedto,● Bycontractingduringvasoconstrictiontoreducebloodflow,andrelaxingduringvasodilationtoincreasebloodflow. (b)● Veinshavesemi-lunarvalves. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q7.(a)(i) (ii)● ThenumberofpeopleworldwidewhohadHIVincreasedfrom2010at33.2millionto36.7millionin2016,anincreaseof3.5million.● From2010to2011,theincreaseof33.2to33.7was0.5million,whichislesssteepcomparedtothechangefrom2011to2016,● wheretherewasaslightlysteeperandlinearincreaseof0.6millioneachyear. (b)● Usecondomswhenengaginginsexualintercourse.● Onlyengageinsexualintercoursewithonepartnerwhoisknowntobefreeofsexuallytransmitteddiseases.● Donotshareunsterilisedneedles. Stillwantmore?www.thatbiotutor.com- www.instagram.com/thatbiotutor/-www.youtube.com/@thatbiotutor- www.tiktok.com/@thatbiotutor

Credit:WrittenbythecollectiveeffortofourtutorsatThatBioTutor. Youarewelcometosharethesewithanyoneyou’dlike!Justdon’tsellthemforprofit:) Q8.(a)● Thepresenceofforestfiresactsaselectionpressure.● Asthereisvariationbetweeneucalyptustrees,someofthemhadafire-resistanceallele,● Whichisafavourabletraitasitallowsthemtosurvivefires,givingthemaselectiveadvantage.● Asaresult,theseindividualssurvivedandreproducedmore,passingontheirfavourablefire-resistanceallelestotheiroffspring.● Overalongperiodoftime,accumulationofnewgenesbymutationandnaturalselectionresultedintheevolutionofeucalyptustreestoberesistanttofires. (b)(i) ● Theprocesswherebyhumansselectivelychoosewhichindividualstobreedinordertoachievedesirabletraits. (ii) Animal:Cows● Feature: