剑桥雅思8-第三套试题-阅读部分-PASSAGE-3VIP免费

剑桥雅思8-第三套试题-阅读部分-PASSAGE3-阅读真题原文部分:READINGPASSAGE3Youshouldspendabout20minutesonQuestions27—40,whicharebasedonReadingPassage3onthefollowingpages.Questions27-32ReadingPassage3hassevenparagraphs,A-G.ChoosethecorrectheadingforparagraphsB-Gfromthelistofheadingsbelow.Writethecorrectnumber,i-x,inboxes27-32onyouranswersheet.ListofHeadingsiThebiologicalclockiiWhydyingisbeneficialiiiTheageingprocessofmenandwomenivProlongingyourlifevLimitationsoflifespanviModesofdevelopmentofdifferentspeciesviiAstablelifespandespiteimprovementsviiiEnergyconsumptionixFundamentaldifferencesinageingofobjectsandorganismsxRepairofgeneticmaterialExampleAnswerParagraphAv27ParagraphB28ParagraphC29ParagraphD30ParagraphE31ParagraphF32ParagraphGHOWDOESTHEBIOLOGICALCLOCKTICK?AOurlifespanisrestricted.Everyoneacceptsthisas'biologically'obvious.'Nothinglivesforever!'However,inthisstatementwethinkofartificiallyproduced,technicalobjects,productswhicharesubjectedtonaturalwearandtearduringuse.Thisleadstotheresultthatatsometimeorothertheobjectstopsworkingandisunusable('death'inthebiologicalsense).Butarethewearandtearandlossoffunctionoftechnicalobjectsandthedeathoflivingorganismsreallysimilarorcomparable?BOur'dead'productsare'static',closedsystems.Itisalwaysthebasicmaterialwhichconstitutestheobjectandwhich,inthenaturalcourseofthings,isworndownandbecomes'older'.Ageinginthiscasemustoccuraccordingtothelawsofphysicalchemistryandofthermodynamics.Althoughthesamelawholdsforalivingorganism,theresultofthislawisnotinexorableinthesameway.Atleastaslongasabiologicalsystemhastheabilitytorenewitselfitcouldactuallybecomeolderwithoutageing;anorganismisanopen,dynamicsystemthroughwhichnewmaterialcontinuouslyflows.Destructionofoldmaterialandformationofnewmaterialarethusinpermanentdynamicequilibrium.Thematerialofwhichtheorganismisformedchangescontinuously.Thusourbodiescontinuouslyexchangeoldsubstancefornew,justlikeaspringwhichmoreorlessmaintainsitsformandmovement,butinwhichthewatermoleculesarealwaysdifferent.CThusageinganddeathshouldnotbeseenasinevitable,particularlyastheorganismpossessesmanymechanismsforrepair.Itisnot,inprinciple,necessaryforabiologicalsystemtoageanddie.Nevertheless,arestrictedlifespan,ageing,andthendeatharebasiccharacteristicsoflife.Thereasonforthisiseasytorecognise:innature,theexistentorganismseitheradaptorareregularlyreplacedbynewtypes.Becauseofchangesinthegeneticmaterial(mutations)thesehavenewcharacteristicsandinthecourseoftheirindividuallivestheyaretestedforoptimalorbetteradaptationtotheenvironmentalconditions.Immortalitywoulddisturbthissystem-itneedsroomfornewandbetterlife.Thisisthebasicproblemofevolution.DEveryorganismhasalifespanwhichishighlycharacteristic.Therearestrikingdifferencesinlifespanbetweendifferentspecies,butwithinonespeciestheparameterisrelativelyconstant.Forexample,theaveragedurationofhumanlifehashardlychangedinthousandsofyears.Althoughmoreandmorepeopleattainanadvancedageasaresultofdevelopmentsinmedicalcareandbetternutrition,thecharacteristicupperlimitformostremains80years.Afurtherargumentagainstthesimplewearandteartheoryistheobservationthatthetimewithinwhichorganismsageliesbetweenafewdays(evenafewhoursforunicellularorganisms)andseveralthousandyears,aswithmammothtrees.EIfalifespanisageneticallydeterminedbiologicalcharacteristic,itislogicallynecessarytoproposetheexistenceofanint...