资源描述：
《25个考研英语阅读经典试题及答案(12)生物学类》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、25个考研英语阅读经典试题及答案(12)SAMPLE12[生物学类]题目序号题型归类第1题细节推导题型第2题写作手法题型第3题审题定位与中心主旨题型第4题词汇题型第5题审题定位题型Flatfish,suchastheflounder,areamongthefewvertebratesthatlackapproximatebilateralsymmetry(symmetryinwhichstructurestotheleftandrightofthebody’smidlinearemirrorimages).Moststrikingamongthemanyasymmetrie
2、sevidentinanadultflatfishiseyeplacement:beforematurityoneeyemigrates,sothatinanadultflatfishbotheyesareonthesamesideofthehead.Whileinmostspecieswithasymmetriesvirtuallyalladultssharethesameasymmetry,membersofthestarryflounderspeciescanbeeitherleft-eyed(botheyesontheleftsideofhead)orright-e
3、yed.InthewatersbetweentheUnitedStatesandJapan,thestarryflounderpopulationsvaryfromabout50percentleft-eyedofftheUnitedStatesWestCoast,throughabout70percentleft-eyedhalfwaybetweentheUnitedStatesandJapan,tonearly100percentleft-eyedofftheJapanesecoast.Biologistscallthiskindofgradualvariationov
4、eracertaingeographicrangea“cline”andinterpretclinesasstrongindicationsthatthevariationisadaptive,aresponsetoenvironmentaldifferences.Forthestarryflounderthisinterpretationimpliesthatageometricdifference(betweenfishthataremirrorimagesofoneanother)isadaptive,thatleft-eyednessintheJapanesesta
5、rryflounderhasbeenselectedfor,whichprovokesaperplexingquestion:whatistheselectiveadvantageinhavingbotheyesononesideratherthanontheother?Theeasewithwhichafishcanreversetheeffectofthesidednessofitseyeasymmetrysimplybyturningaroundhascausedbiologiststostudyinternalanatomy,especiallytheopticne
6、rves,fortheanswer.Inallflatfishtheopticnervescross,sothattherightopticnerveisjoinedtothebrain’sleftsideandviceversa.Thiscrossingintroducesanasymmetry,asoneopticnervemustcrossaboveorbelowtheother.G.H.Parkerreasonedthatif,forexample,aflatfish’slefteyemigratedwhentherightopticnervewasontop,th
7、erewouldbeatwistingofnerves,whichmightbemechanicallydisadvantageous.Forstarryflounders,then,theleft-eyedvarietywouldbeselectedagainst,sinceinastarryfloundertheleftopticnerveisuppermost.TheproblemwiththeaboveexplanationisthattheJapanesestarryflounderpopulationi
