2014-03-02Reading细胞理论+动物调节体温方式

spunglass：玻璃纤维cork:n.软木；软木塞；(钓鱼用)软木浮子；［植］外皮tartar:Tartarisahardyellowishsubstancethatformsonyourteethandcausesthemtodecayifitisnotremoved.牙垢；牙结石；［化］酒石CellTheoryThestudyofcells--cellbiology--beganin1660,whenEnglishphysicistRobertHookemeltedstrandsofspunglasstocreatelensesthathefocusedonbeestingers,fishscales,flylegs,feathers,andanytypeofinsecthecouldholdstill.Whenhelookedatcork,whichisthebarkfromatypeofoaktree,itappearedtobedividedintolittleboxes,whichwereremnantsofcellsthatwereoncealive.Hookecalledtheseunits"cells"becausetheylookedlikethecubicles(cellae)wheremonksstudiedandprayed.AlthoughHookedidnotrealizethesignificanceofhisobservation,hewasthefirstpersontoseetheoutlinesofcells.In1673,AntonyvanLeeuwenhoekofHollandimprovedlensesfurther.Heusedonlyasinglelens,butduetoitsquality,itwasmoreeffectiveatmagnifyingandproducedaclearerimagethanmosttwo-lensmicroscopesthenavailable.Oneofhisfirstobjectsofstudywastartarscrapedfromhisownteeth,andheobservedthatitcontainedmanyverysmallanimalcules(microscopicorganisms).Overthenextfewyears,Leeuwenhoekbuiltmorethan500microscopesthatopenedavastnewworldtothehumaneyeandmind.Heviewedbacteriaandothermicroorganisms--lifethatpeoplehadnotknownexisted.However,hefailedtoseethesingle-celled"animalcules"reproduce,andthereforeheperpetuatedthepopularideaatthetimethatlifearisesfromthenonlivingorfromnothing.Nevertheless,hedescribedwithremarkableaccuracymicroorganismsandmicroscopicpartsoflargerorganisms,includinghumanredbloodcells.Despitetheaccumulationofmicroscopists'drawingsofcellsmadeduringtheseventeenthandeighteenthcenturies,thecelltheory--theideathatthecellisthefundamentalunitofalllife--didnotemergeuntilthenineteenthcentury.Historiansattributethedelaytopoortechnology--forexample,crudemicroscopesandalackofprocedurestopreserveandstudylivingcellswithoutdamagingthem.Neithertheevidenceitselfnorearlyinterpretationsofitsuggestedthatallorganismswerecomposedofcells.Hookehadnotobservedactualcellsbutratherwhattheyhadleftbehind:thecellwalls.Leeuwenhoekmadeimportantobservations,buthedidnotmethodicallydescribeorcategorizethestructuresthatcellshadincommon.Inthenineteenthcentury,morepowerfulmicroscopes,withbettermagnificationandillumination,revealeddetailsoflifeatthesubcellularlevel.Intheearly1830s,ScottishsurgeonRobertBrownnotedaroughlycircularstructureincellsfromorchidplants.Findingthestructureineveryorchidcell,hethenidentifieditinallcellsfromavarietyofotherorganisms.Henameditthe"nucleus,"atermthathadremainedinuse.Brownmemorializedtheimportanceofthestructurehediscovered,buttodayweknowthenucleushousesDNAforcomplexcells.Thecelltheoryfinallyemergedin1839whenGermanbiologistsMatthiasJ.SchleidenandTheodoreSchwannmadecarefulcomparisonsofplantsandanimals.Schleidenfirstnotedthatcellswerethebasicunitsofplants,andthenSchwanncomparedanimalcellstoplantcells.Afterobservingmanydifferentplantandanimalcells,theyconcludedthatcellswere“elementaryparticlesoforganisms,theunitofstructureandfunction."SchleidenandSchwanndescribedthecomponentsofthecellasacellbodyandnucleuscontainedwithinasurroundingmembrane.Schleidencalledacella“peculiarlittleorganism”andrealizedthatacellcanbealivingentityonitsown;butthenewtheoryalsorecognizedthatinlargeplantsandanimals,cellsarepartofalargerlivingorganism.ManycellbiologistsextendedSchleidenandSchwann’sobservationsandideas.GermanphysiologistRudolphVirchowaddedtheimportantcorollaryin1855thatallcellscomefrompreexistingcells,contradictingthestill-popularideathatlifecanarisefromthenonlivingorfromnothingness.Virchow’sstatementalsochallengedthepopularconceptthatcellsdevelopontheirownfromtheinsideout,thenucleusformingacellbodyarounditself,andthenthecellbodygrowingacellmembrane.Virchow’sobservationsetthestagefordescriptionsofcelldivisioninthe1870sand1880s.Virchowwasaheadofhistimebecausehehypothesizedthatabnormalcellscausediseasesthataffectthewholebody.词汇题：remnants：wallsremainsreflectionsstructuresAccordingtoparagraph2,whichofthefollowingdidAntonyvanLeeuwenhoekNOTdo?observebacteriawatchsingle-celledorganismsreproducefeelindividualcellsoflargerorganismsinspectmaterialsscrapedfromhisteethunderalensWhichofthefollowingstatementsaboutmicroscopesissupportedbytheinformationpresentedinparagraph2?two-lensmicroscopeswerenotavailableinHollandinLeeuwenhoek'stimeLeeuwenhoekpreferredtwo-lensmicroscopestoone-lensmicroscopesThequalityofLeeuwenhoek'smicroscopewasbetterthanthatofmosttwo-lensmicroscopesavailablein1673two-lensmicroscopeswereinventedbyLeeuwenhoekWhydoestheauthorstatethat"Leeuwenhoekfailedtoseethesingle-celled“animalcules”reproduce”？toarguethatLeeuwenhoekintentionallyignoredsomeofwhathesawwithhismicroscopetosuggestthatLeeuwenhoekwasnotasimportantaresearcherashehastraditionallybeenconsideredtoexplainwhyLeeuwenhoekdidnotchallengetheideathatlifecouldemergefromnonlivingmaterialtocontrastLeeuwenhoek'sobservationswiththoseofearlierresearchersTheGreatDepressionThetermtheGreatDepressionreferstothesevereeconomiccrisisofthe1930sthataffectedtheUnitedStatesandeventuallymuchoftheworld.Itisconsideredtheworstandlongestperiodofhighunemploymentandlowbusinessactivityinmoderntimes.The1920swasaperiodofgreatprosperityintheUnitedStates.DuringthisperiodmanyAmericansopposedgovernmentregulationoftheeconomyinprinciple.Theybelievedthatinperiodsofeconomicsetbackthegovernmentshouldcutexpendituresandwaitfortheeconomytoimprove.ThisprevailingattitudewastochangeprofoundlybythetimetheGreatDepressionwasover.By1929,manyweaknessesintheAmericaneconomybecameevident.Theprospectforconstructionwasadverselyaffectedbytherisingcoistsofconstructionandland.Farmerswerefacingdifficultiesassurplusesdepressedpricesforagriculturalproducts.Consequentlythepotentialmarketforconsumergoodsinfarmareasdriedupandbanksandotherfinancialinstitutionswithloansoutstandingtofarmerswereweakened.Manypeoplelackedsavings.Anemploymentinsurance,orothercushionswerevulnerabletoeconomicadversity.Especiallyiftheyhadboughtgoodsoncreditasadvertisementshadurgedthemtodo.Andwhentheysuffered,sodidthemanufacturersandretailerswhoservedthem.ThemostdramaticandobviouscauseoftheDepressionwasthecollapseofthestockmarketin1929.Duringtheprosperousyearsbetween1925and1929stockmarketpricesroseaboutthreehundredpercent.By1929overamillionstockbuyerswereforcingpricestorisemuchfasterthancorporateprofits.Itwasaprocessthatcouldnotcontinueindefinitely.InoneterrriblemonthstartingonOctober24,1929(nowknownasblackThursday),pricesontheNewYorkStockExchangealonefellinvalueabout26milliondollars,adeclineofninepercent,andpricesproceededdownwardforanothertwoandhalfyearsuntilby1932thestockmarkethadlostnearlyninetypercentofitsvalue.ItseemssafetoassertthattheenormouslossofwealthbyindividualsandinstitutionsplayedamajorroleinthesubsequentfailureoftheUnitedStateseconomy.TheDepressionpassedthroughtodistinctstages.Thefirst,whichlastedfrom1929to1931,wasaperiodofreducedeconomicactivity.In1930forexample,industrialproductionwasonly26percentbelowitspeaklevelof1929.Thesecondstagewasmuchmoresevere;itlastedfrom1931until1936.ThisstagewasrelatednotonlytodomesticeventsbutalsotoseriousfinancialproblemsinGermany,AustriaandGreatBritainthatwereinducedprimarilybyasharpdeclineinAmericaninvestment,purchasing,andlendingabroad.Internationalcommoditypricesfelltoabsurddepth.RepercussionsweresevereintheUnitedStates,especiallyonagriculturalpricesandonbankswithextensiveforeignholdings.Some2,300bankswithdepositsofnearly1.7billiondollarfailedintheUnitedStatesin1931.Itwasaneconomiccatastrophe.From1929to1933nationalincomedeclinedfrom87.8billiondollarto40.2billiondollar.Morethan100,000businessesfailed.Thenumberofunemploymentswelledto14millionbyearly1933.Farmincome,salaries,andmanufacturingwagesplummeted.ThetraumaoftheGreatDepressionwasdevastating.Twotothreemillionpeoplemovedfromcitiesbacktothecountryinthehopeofbeingabletoscratchabarelivingfromthesoil.Familytensionsmultiplied,thenumberofmarriagesandbirthdeclined,andpovertygenerallyincreased.Oneofthemostsignificantlong-termimpactswasthechangethatitbroughtinattitudestowardbusinessandgovernment.Lossofapopularconfidenceinthenation'sbusinessandfinancialleadershipwasalmostcompleteby1933.Lackoftrustincreasedparticularlyafterseveralinvestigationsrevealedtheextenttowhichbankershadmisuseddepositors'moneyandmanipulatedthestockmarketduringthe1920s.Indeed,investmentbankers,alongwithPresidentHubertHoover,becamethechiefscapegoatsofthedebacle.Gradually,Americansbegantolooktothegovernmentforprotection.By1935amajorityofAmericansfinallyconcludedthatthegovernmentshouldprovidejobsfortheunemployedwheneverprivatebusinessesputunabletodoso.Theoldsystemofrelativelyunregulatedfreeenterprisehadtogivewaytoanewsystemofgovernmentintendingtoassurethesuccessfulfunctioningoftheeconomy.poikilotherm：n.变温动物homeotherm:n.恒温动物paramecia:n.草履虫(复数形式)amoebas：n.变形虫millipede:n.百足虫，马陆glycerol:［化］甘油diapause:n.［生］滞育(昆虫生长的停滞期)；间歇期PoikilothermsPhysiologically,animalscanbedividedintothreegroups:homeotherms,whichmaintainafairlyconstantinternaltemperatureregardlessoftheexternaltemperature;poikilotherms,whichhaveabodytemperaturethatvariesaccordingtothesurroundingenvironmentaltemperature;andheterotherms,whichsometimesmaintainafairlyconstantbodytemperatureandsometimesdonot.Poikilotherms,suchasamphibiansandinsects,haveahighthermalorheatconductancebetweenthebodyandtheenvironment,andalowmetabolicrate.Forthisreasonbodytemperature__andthustissuetemperaturechangeswithenvironmentaltemperature.Beingectothermicandmanitainingbodytemperaturebyusingsourcesofheatenergysuchassolarradiationratherthanmetabolismhasadvantages.Prisonersofenvironmentaltemperatures,poikilothermsoftemperateregions,suchassnakes,becomehighlyactiveonlywhentemperatureisadequatelywarm.Becausetheirmetabolicactivitydeclineswithdecreasingtemperature,theseanimalsbecomesluggishinthecoolofmorningandevening.Similarly,theyhavetorestricttheiractivitytothelatespring,summerandearlyfall.Duringperiodsofintensephysicalactivity,whenenergyconsumptionishigh,poikilothermsdependontheanaerobic(withoutoxygen)breakdownofglycogen(sugarsstoredforenergy).Thesebreakdownresultsinanaccumulationoflacticacidinthetissues,andthelacticacidcanbeoxidisedonlyafteractivityceases.Anaerobicmetabolismseverelylimitsburstsofpoikilothermicactivitytoafewminutes,becauseofphysicalexhaustion.Thistendancytobecomeexhaustedisonereasonthatsomanypredatoryterrestrialpoikilotherms,suchassnakesandalligators,securepreybyambushratherthanbychase.Becausetheydonotdependoninternallygeneratedbodyheat,poikilothermscanreducemetabolicactivityduringperiodsoftemperatureextremesandoffoodorwatershortage.Lowenergydemandsenablepoikilothermstocolonizeareasoflimitedfoodandwater,suchasdeserts.Becausetheydonothavetheproblemofmetabolicheatloss,poikilothermsarenotlimitedtoanyminimumsizeordefiniteshape.Manyaresinglecelled,suchasparameciaandamoebas;otherssuchasearthworms,millipedes,andsnakeshavecylindricalbodies.Suchcharacteristicsenablepoikilothermstoexploitresourcesandhabitatsunavailabletohomeotherms.Ontheotherhand,thesamemetabolicrestrictionsimposedanuppersizelimit:poikilothermswouldnotbeabletoobsorbenoughheattowarmaverylargebody.Forthisreason,somepaleontologistsarguethatlargedinosaurshadtobeendothermic(maintainingaconstantbodytemperaturebymeansofmetabolism).Acounterargumentisthatlargeectothermscoulddevelopandmaintainbodytemperaturesaboveairtemperaturesinatropicalenvironmentbecausetheirlowsurface-to-volumeratiowouldlimitcooling.Althoughpoikilothermsasagroupdonothavealowerlimittobodysize,sizeisneverthelessanimportantaspectoftheirlife.Therateofheatingandcoolinginapoikilothermdecreasesasthesizeincreases.Becauseofitssmallsize,abeetleheatsandcoolsquickly,butrarelycanitraiseitsuniformtemperatureabovethatofthesurroundingenvironmentaltemperature.However,itdoeshavetheabilitytocontrolitstemperaturebymovinginandoutofthesunlig