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1、考博英语强化阶段自测题PART1READINGCOMPREHENSIONPassage1Cellscannotremainaliveoutsidecertainlimitsoftemperature,andmuchnarrowerlimitsmarktheboundariesofeffectivefunctioning.Enzyme(酶)systemsofmammalsandbirdsaremostefficientonlywithinanarrowrangearound37ºC;adepartureofafewdegreesfromthisval
2、ueseriouslyimpairstheirfunctioning.Eventhoughcellscansurvivewiderfluctuations,theintegratedactionsofbodilysystemsareimpaired.Otheranimalshaveawidertoleranceforchangesofbodilytemperature.Forcenturiesithasbeenrecognizedthatmammalsandbirdsdifferfromotheranimalsinthewaytheyregulat
3、ebodytemperatures.Waysofcharacterizingthedifferencehavebecomemoreaccurateandmeaningfulovertime,butpopularterminologystillreflectstheolddivisioninto“warm-blooded’and“cold-blooded”species;warm-bloodedincludedmammalsandbirds,whereasallothercreatureswereconsideredcold-blooded.Asmo
4、respecieswerestudied,itbecameevidentthatthisclassificationwasinadequate.Afencelizardoradesertiguana(鬣蜥)—eachcold-blooded—usuallyhasabodytemperatureonlyadegreeortwobelowthatofhumansandsoisnotcold.Thereforethenextdistinctionwasmadebetweenanimalsthatmaintainaconstantbodytemperatu
5、re,calledhomotherms（同温动物）,andthosewhosebodytemperaturevarieswiththeirenvironment,calledpoikilotherms(变温动物).Butthisclassificationalsoprovedinadequate,becauseamongmammalstherearemanythatvarytheirbodytemperaturesduringhibernation.Furthermore,manyinvertebrates(无脊椎动物)thatliveinthed
6、epthsoftheoceanneverexperienceachangeinthechillofthedeepwater,andtheirbodytemperaturesremainconstant.Thecurrentdistinctionisbetweenanimalswhosebodytemperatureisregulatedchieflybyinternalmetabolicprocessesandthosewhosetemperatureisregulatedby,andwhogetmostoftheirheatfrom,theenv
7、ironment.Theformerarecalledendotherms(恒温动物),andthelatterarecalledectotherms(外温动物).Mostectothermsdoregulatetheirbodytemperature,andtheydosomainlybylocomotingtofavorablesitesorbychangingtheirexposuretoexternalsourcesofheat.Endotherms(mainlymammalsandbirds)alsoregulatetheirtemper
8、aturebychoosingfavorableenvironments,butprimarilytheyregulate
