1990HKALPaperIIWord格式文档下载.docx

1990HKALPaperIIWord格式文档下载.docx

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hencetherespirationratewillincrease/doubleaccording1

totheQ10rule/explanationofincreasingtemperatureonrateofenzymicreaction.1

（4）

（c）Aquaticectothermswillbemoreaffectedsinceanincreaseinwatertemperaturewilldecreasethesolubilityofdissolvedoxygeninwater,makingoxygenlessavailable（NOTE:

saturatedvalueofdissolvedoxygendecreasesfrom6.19to5.27ml/linfreshwaterandfrom5.35to4.5ml/lin30%seawaterwhenwatertemperatureincreasesfrom20to30C）whileatthesametime,therespirationrate（andhenceoxygendemand）oftheanimalwilldouble/increase.

（2）

（d）Therateanddepthofbreathingarecontrolledbyarespiratorycentreinthemedulls,1

whichisresponsivedirectlyorindirectly（throughchemoreceptors:

theaorticandcarotidbodiesinthewallsofmajorarteries）tochangesinCO2,H+andO2concentrationsinblood.1

AnincreaseintheconcentrationofCO2andH+inthebloodstimulatestherespiratorycentrewhichinturn,increasesdepthofbreathing（andviceversa）1

Lackofoxygenstimulateschemoreceptorsincarotidandaorticbodyandstimulatesrespiration.Oxygenreceptorshowever,aresensitiveonlytolargechangesinbloodPO2（<

70mmHg）andislittleaffectedbyslightchangesofoxygeninblood.1

SinceoxygeninbloodPCO2andPO2normallyareproportionaltooneanother,breathingisgenerallyregulatedbyCO2inblood.

（4）

（e）Thesmallertheanimal,thefartheritsoxygendissociationcurve-isshiftedtotheright.1

Thehaemoglobinofsmallanimalsthereforeunloadsmoreofitsoxygenatanygivenpressurethandoesthehaemoglobinofalargeranimal.1

Heatlossfromanendothermisproportionaltoitsbodysurfacearea.Thesmallertheanimal,thelargerisitsS.A./Vratioandhenceitsrateofheatloss1

Inordertocompensateforthehigherrateofheatlosstomaintainaconstantbodytemperature,thesmalleranimalneedstohaveahighermetabolicrate1

Theshiftingofthecurvetotherightallowssmallanimalstoobtainmoreoxygentosustaintheirhighermetabolicratesatanygivenoxygenpartialpressure.（NOTE:

partialpressureofoxygeninairandthelungisnormallyhigherthan100mmHg,andanimalsofallsizeshouldhavetheirhaemoglobinfullysaturatedwithoxygenatsuchpartialpressure）1

（5）

2.（a）Nomotileantherozoids/spermssodonotneedfreewaterforfertilisation.1

Malegametestransferredinsideresistantpollen.1

Useofwindoranimalsforpollentransfer.1

Ovulesenclosedinovary/carpels.1

Embryoprotectedinseed.1

（b）Sexualreproduction:

advantages－geneticvariationfromrandomassortmentandcrossingoverduringmeiosis1

－widedispersalofseeds1

disadvantages－dependentonsuccessfulpollination1

－seedmustcarryownfoodstore1

Vegetativereproduction:

advantages－morereliableasnoneedforpollination1

－offspringcangetcontinuedfoodsupplyfromparentplant1

disadvantages－geneticallysameasparent1

－cannotspreadfarfromparent1

（8）

（c）Wind-dispersedfruitsaredryandtypicallyhavesomesortofextensionofthepericarp（e.g.wings,pappus）toincreaseairresistanceandreducetherateoffall.1

Animal-dispersedfruitsarefleshy（succulent）toattractandrewardanimals,whiletheseedorseedsareprotectedbyatoughcovering（endocarporseedcoat）topreventdamageduringconsumptionofthefruit.1

Colourofwind-dispersedfruitsistypicallybrown（cryptic）.1

Animal-dispersedistypicallybrightlycoloured.1

Somefruitsmaydevelophook-likestructuresorproducestickysecretionssuchthattheyattachveryeasilyontothefurofanimals.1

（d）Dispersalofseeds

－reducesovercrowding（intraspecificcompetition）1）

－enablescolonizationofnewhabitats1）any2

－permitsescapefromspecies-specificpestsanddiseases1）

（2）

3.（a）Airmovement1）

Instillairthereisaboundarylayerofsaturatedairovertheleafsurfacewhichreducestranspiration.Airmovementsreducethethicknessofthisboundarylayerandsoincreasetranspiration.

Relativehumidityoftheatmosphere1）

Thelowertherelativehumiditythegreaterthewaterpotentialgradientbetweenthesaturatedairinsidetheleafandtheairoutside,andthusthehigherthetranspirationrate.

Lightintensity1）

Thestomataofmostplantsopeninthelightandcloseinthedark.Thetranspirationrateismuchhigherwhenthestomataareopenbecausethecuticleactsasabarriertothediffusionofwatervapour.

Airtemperature1）

Ariseintemperatureincreasesthewaterpotentialoftheairinsidetheleafbecauseincreasedevaporationfromthecellwallskeepstheairsaturated.Incontrast,ariseintemperaturewillhavelittleeffectonthewaterpotentialoftheexternalatmosphere.Thusariseintemperatureincreasesthewaterpotentialgradientbetweentheleafandthesurroundingairandhenceincreasestherateoftranspiration.

Soilwater1）

Areductionintheavailabilityofwatertotheplantmeansthatthemesophyllcellswillnotbefullyturgidandthecellwallsnotcompletelywet.Transpirationwillthusbereduced.any4

（6）

（b）－reduceddensityofstomataonleafsurfaces

－athickcuticleand/orwaxlayer-whichreducestherateofwaterlosswhenthestomataareclosed

－stomatasunkeninpitsbelowtheleafsurfacesothattheairoutsidethe-stomataismoresaturatedthanthesurroundingatmosphere（orsothatthethicknessoftheboundarylayerisincreased）

－hairsontheleafsurface-increasingthethicknessoftheboundarylayer

－leafrollingwiththestomatainsideincreasesthehumidityoftheatmosphereoutsidethestomata

－reductioninthesurfacearea/volumeratiooftheplant-reduceswaterlossperunitvolumeoftheplant

－C4orCAMphotosynthesis-increaseswateruseefficiency/openingofstomataatnighttime（4）

（c）Waterlostbytranspirationisreplacedbyevaporationfromthemesophyllcellwalls.waterisinturndrawnfromtheprotoplastsofthemesophyllcells.Theloweredwaterpotentialofthemesophyllcellsresultsinwaterbeingdrawnfromthexylemoftheleafveinswhichisinturndrawnfromthexylemelementsinthestem.Thecohesionofthewatermoleculesensuresthatwateispulledupthestemaslongastranspirationiscontinued.（4）

（d）Ringingexperiments6）

Cylindersofbark,whichincludethesecondaryphloem,areremovedfromwoodystemsandthecontentsofthephloemaboveandbelowtheringareanalysed.Whentheringisbetweenasourceandasinkforcarbohydrates（e.g.betweentheleavesandtheroots）,sucroseaccumulatesinthephloemonthesourcesideoftheringonly.

Aphidstylets（mouthparts）,whichpenetratethephloemelementsareusedtosamplethecontentsofthephloem.Thecompositionofthephloemsapvarieswiththephotosyntheticactivityoftheplant.6）

Photosyntheticallyactivegreenleavesaresuppliedwithcarbondioxidelabelledwiththeradioisotope14C.Thelabelledproductsofphotosynthesisspreadthroughtheplantinthephloem.6）any1

（6）

4.（a）Restingneurone:

1

－membraneishighlypermeabletopotassiumions,butisonlyslightlypermeabletosodiumions;

－membranepotentialisnegativeinsidewithrespect-tooutside:

Excitedneurone:

－membraneishighlypermeabletobothsodiumandpotassiumions;

－membranepotentialispositiveinsidewithrespecttooutside

（2）

（b）（i）nerveimpulsepropagatesalongthewholelengthoftheaxoninanon-decremental（all-or-nothing）manner.1

Mechanism:

4

Theinnersurfaceoftheexcitedmembraneislocallypositive（asaresultofinfluxofsodiumions）.

Potentialdifferencebetweenthisactiveregionandtheadjacentinactivemembrane.

Localcurrentflowslaterallythroughtheaxoplasmfromtheformertothelatterregion,causingdepolarizationoftheinactiveregion.

Whenthisinactiveregionisdepolarizedtothethreshold,itbecomesexcitedautomaticallywiththegenerationofanewactionpotential.

（ii）Diameterofaxon-conductionspeedincreasesasaxondiameterincreases

Myelination-myelinatedaxonhashigherconductionspeedthanunmyelinatedaxon

（2）

（c）Nerveactionpotentialdepolarize