托福作文写作范文详解dvers.docx

托福作文写作范文详解ReadingGeneticmodification,aprocessusedtochangeanorganism'sgenesandhenceitscharacteristics,isnowbeingusedtoimprovetreesthroughgeneticmodification.Itispossibletocreatetreesthatproducemorefruitzgrowfaster,orwithstandadverseconditions.Plantinggeneticallymodifiedtreesonalargescalepromisestobringanumberofbenefits.First,geneticallymodifiedtreesaredesignedtobeharderthannaturetrees;thatisztheyaremorelikelytosurvivethantheirunmodifiedcounterparts.InHawaii,forexample,anewpestresistantspeciesofpapayatreeshasbeendevelopedinresponsetoringspotvirusinfectionsthathaverepeatedlydamagedthenativepapayatreepopulation.Plantingthegeneticallymodifiedpapayashaslargelyputanendtotheringspotproblem.Moreover,geneticallymodifiedtreespromisetobringanumberofeconomicbenefitstothosewhogrowthem.Geneticallymodifiedtreestendtogrowfaster,givegreateryieldsoffoodzfruitzorotherproductsandbehardier.Thisallowstreefarmertogetfasterandgreaterreturnsontheirfarminginvestmentandsaveonpesticidesaswell.Finally,theuseofgeneticallymodifiedtreescanpreventoverexploitationofwildtrees.Becauseofthegrowingdemandforfirewoodandbuildingtimber,manyforestsaroundtheworldarebeingcutdownfasterthantheycanbereplaced.Introducinggeneticallymodifiedtrees,designedforfastgrowthandhighyieldingivengeographicconditions,wouldsatisfythedemandforwoodinmanyofthoseareasandsavetheendangerednativetrees,whichoftenincludeuniqueorrarespecies.ListeningSure,therearesomebenefitstoplantgeneticallymodifiedtrees,but,arethesetreesasreallygreatastheyfirstsound?Whenyouexaminethesubjectfirstly,therearesomeseriousproblemsandcostsassociatedwithgeneticallymodifiedtrees.First,geneticallymodifiedtreesmayberesistanttooneparticularcondition.Butthatdoesnjtnecessarilyensuretheirsurvival.Youseezatypicalnonmodifiedtrees'populationisgeneticallydiverse.Thatmeansthatformostthreateningconditions,orclimate,whatever,therewillbeatleastsomeindividualtressofanygivenspeciesoftreethatareresistant.Soevenifmostofonekindoftreesarekilled,thosefewresistanttresswillsurviveandensurethesurvivalofthatspeciesoftree.Butgeneticallymodifiedtreesaregeneticallymuchmoreuniform.Soifthey'reexposedtoanenvironmentalchallengetheyhavenotbeendesignedfor,theyalldie.Soiftheclimatechanges,thegeneticallymodifiedtreeswilllikelytobecompletelywipedout.Nowastothesecondpointzthey,rehiddencostsassociatedwithgeneticallymodifiedtrees.Yousee,thecompanythatgeneticallymodifythetreecanchargetreefarmersmoreforitsseedsthanun-geneticallymodifiedtreeswouldcost.Alsozasyou,vegrownthetree,youcan,tjustcollecttheseedsandplantthenewtreeforfree.ByIawzyouhavetopaythecompanyeverytimeyouplant.Andfinally,geneticallymodifiedtreesmightactuallycauseevenmoredamagetothelocalwildtrees.Youseezgeneticallymodifiedtreesoftengrowmoreaggressivelythannaturaltreesdo.And,geneticallymodifiedtreesaretypicallyplantedamongnaturaltrees.Asaresult,thegeneticallymodifiedtreesOutcompetethenativetreesforresources,sunlight,soil,nutrients,andwater,eventuallycrowdingoutthenaturaltrees.一、阅读听力要点概括ReadingPassageMainpoints:Geneticmodificationonlargescalewillbringbenefits.Subpoint1:Canbecompletelywipedoutbycertainenvironment.Subpoint2:Modifiedtreesareeconomicallybetter.Subpoint3:Modifiedtreesgrowfastandsavewildtrees.LectureAttitude:Against(Seriousproblemandassociatedcost.)SubPoint1:Thereareeffectivewaystostopmusselsintoday'sknowledgeSubPoint2:Hiddencostsassociatedlikeseeds.SubPoint3:Domoredamagetowildtrees.GrowsofastandOutcompetethewildtree.二、范文逐段贯析Paragraph1Thelecturerpointsoutthreedifferentshortcomingsofgeneticallymodifiedtrees.Intheaspectsofadaptation,economicIucrativeness,andenvironmentalvalue,theyneverpresentoverwhelmingadvantagescomparedwithnaturaltrees.Thismeansthepointsmadeinthereadingarepartialandbiased.此段功能：（Listeningpassage后文提到用L代替）（Readingpassage后文用R代替）文章首先总结了三个分论点，十分新颖。三个分论点从三方面出发，环境适应性，经济有利性，环保价值性。然后写到L告诉大家R在三个方面的观点都是片面的，改造树和野生树在这三方面的比较并没显出绝对优势。确认了相反的逻辑关系，准备开始辩论。此段结构：此段为分总结构，列举三个要讨论的方面，然后才说L对R的意见,为接下来的辩论做好了充足的准备。Paragraph2First,geneticmodificationdoesnztnecessarilymakeanaturaltreemoreresistanttoenvironmentaladversities.Althoughgeneticmodificationmayallowaspeciestomanifestcertainstrengthsinspecificconditions,asthereadingindicates,thenewtypelacksthegeneticdiversityofanaturalspecies.Thankstothemarginaldifferencesbetweenindividualtrees,therecanalwaysbesomesurvivorsamongnaturalspeciesfollowingalargeinterruptionlikeclimatechangeorpestinvasion.Butsuchchangesmaycausethedistinctionofageneticallymodifiedspeciesfortheirunificationincharacteristics,decreasingtheiroverallsurvivabilityinmanycases.此段功能：讨论第一个环境适应性方面的论点。L指出改造树并不一定在任何情况下都比野生树更强壮。因为改造树的基因非常单一，而不像野生树一样随机分布。在新恶劣天气情况下，改造树可能因为没有对抗基因而全部死亡,野生树里却千差万别，相对应的个体树会存活而不会导致与灭族。所以改造树的整体存活率是不高的。此段结构：此段为总分结构，陈列证据十分对称，Althoughbut句型很好的列举了相对立的观点和证据。最后证明R之前的论点不可取。Paragraph3Second,treefarmersdonztgetguaranteedeconomicbenefitsiftheyplantgeneticallynewstrains.Companiesthatdevelopnewplantsalwayschargefarmershigherpricesforartificiallyimprovedseedszandreceivemoneyfromfarmerseachtimefa