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ID:7768135
大小:138.08 KB
页数:22页
时间:2018-02-23
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1、0308托福试题阅读(55minutes)Question1-11Iffoodisallowedtostandforsometime,itputrefies.Whentheputrefiedmaterialisexaminedmicroscopically,itisfoundtobeteemingwithbacteria.Wheredothesebacteriacomefrom,sincetheyarenotseeninfreshfood?Evenuntilthemid-nineteenthcent
2、ury,manypeoplebelievedthatsuchmicroorganismsoriginatedbyspontaneous(5)generation,ahypotheticalprocessbywhichlivingorganismsdevelopfromnonlivingmatter.ThemostpowerfulopponentofthetheoryofspontaneousgenerationwastheFrenchchemistandmicrobiologistLouisPast
3、eur(1822-1895).Pasteurshowedthatstructurespresentinaircloselyresemblethemicroorganismsseeninputrefyingmaterials.Hedid(10)thisbypassingairthroughguncottonfilters,thefibersofwhichstopsolidparticles.Aftertheguncottonwasdissolvedinamixtureofalcoholandether
4、,theparticlesthatithadtrappedfelltothebottomoftheliquidandwereexaminedonamicroscopeslide.Pasteurfoundthatinordinaryairtheseexistsavarietyofsolidstructuresranginginsizefrom0.01mmtomorethan1.0mm.Manyofthesebodiesresembled22thereproductive(15)structuresof
5、commonmolds,single-celledanimals,andvariousothermicrobialcells.Asmanyas20to30ofthemwerefoundinfifteenlitersofordinaryair,andtheycouldnotbedistinguishedfromtheorganismsfoundinmuchlargernumbersinputrefyingmaterials.Pasteurconcludedthattheorganismsfoundin
6、putrefyingmaterialsoriginatedfromtheorganizedbodiespresentintheair.Hepostulatedthatthesebodiesareconstantly(20)beingdepositedonallobjects.Pasteurshowedthatifanutrientsolutionwassealedinaglassflaskandheatedtoboilingtodestroyallthelivingorganismscontamin
7、atingit,itneverputrefied.Theproponentsofspontaneousgenerationdeclaredthatfreshairwasnecessaryforspontaneousgenerationandthattheairinsidethesealedflaskwasaffectedinsomeway(25)byheatingsothatitwouldnolongersupportspontaneousgeneration.Pasteurconstructeda
8、swan-neckedflaskinwhichputrefyingmaterialscouldheheatedtoboiling,butaircouldreenter.Thebendsintheneckpreventedmicroorganismsfromgettingintheflask..Materialsterilizedinsuchaflaskdidnotputrefy.1,Whatdoesthepassagemainlydiscuss?(a)Pasteur’
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