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1、智课网TOEFL备考资料文勇黄金阅读最新版：生物钟摘要：刘文勇新托福黄金阅读最新版文本及答案，高清PDF格式支持免费下载，一共71篇，包括原刘文勇黄金阅读29篇，下面是文勇黄金阅读最新版：生物钟，希望对大家备考托福阅读考试有所帮助。文勇黄金阅读最新版：BiologicalClocks生物钟Survivalandsuccessfulreproductionusuallyrequiretheactivitiesofanimalstobecoordinatedwithpredictableeventsaroundthem.Consequently,
2、thetimingandrhythmsofbiologicalfunctionsmustcloselymatchperiodiceventslikethesolarday,thetides,thelunarcycle,andtheseasons.Therelationsbetweenanimalactivityandtheseperiods,particularlyforthedailyrhythms,havebeenofsuchinterestandimportancethatahugeamountofworkhasbeendoneonth
3、emandthespecialresearchfieldofchronobiologyhasemerged.Normally,theconstantlychanginglevelsofananimal'sactivity—sleeping,feeding,moving,reproducing,metabolizing,andproducingenzymesandhormones,forexample—arewellcoordinatedwithenvironmentalrhythms,butthekeyquestioniswhetherthe
4、animal'sscheduleisdrivenbyexternalcues,suchassunriseorsunset,orisinsteaddependentsomehowoninternaltimersthatthemselvesgeneratetheobservedbiologicalrhythms.Almostuniversally,biologistsaccepttheideathatalleukaryotes(acategorythatincludesmostorganismsexceptbacteriaandcertainal
5、gae)haveinternalclocks.Byisolatingorganismscompletelyfromexternalperiodiccues,biologistslearnedthatorganismshaveinternalclocks.Forinstance,apparentlynormaldailyperiodsofbiologicalactivityweremaintainedforaboutaweekbythefungusNeurosporawhenitwasintentionallyisolatedfromallge
6、ophysicaltimingcueswhileorbitinginaspaceshuttle.Thecontinuationofbiologicalrhythmsinanorganismwithoutexternalcuesatteststoitshavinganinternalclock.Whencrayfisharekeptcontinuouslyinthedark,evenforfourtofivemonths,theircompoundeyescontinuetoadjustonadailyschedulefordaytimeand
7、nighttimevision.Horseshoecrabskeptinthedarkcontinuouslyforayearwerefoundtomaintainapersistentrhythmofbrainactivitythatsimilarlyadaptstheireyesonadailyscheduleforbrightorforweaklight.Likealmostalldailycyclesofanimalsdeprivedofenvironmentalcues,thosemeasuredforthehorseshoecra
8、bsintheseconditionswerenotexactly24hours.Sucharhythmwhoseperiodisapproximately—but
