精品学习网收集整理了，2013年考研英语阅读理解经典练习（生物学类），希望对大家有所帮助！

SAMPLE12

[生物学类]

Flatfish,suchastheflounder,areamongthefewvertebratesthatlackapproximatebilateralsymmetry(symmetryinwhichstructurestotheleftandrightofthebody’smidlinearemirrorimages).Moststrikingamongthemanyasymmetriesevidentinanadultflatfishiseyeplacement:beforematurityoneeyemigrates,sothatinanadultflatfishbotheyesareonthesamesideofthehead.Whileinmostspecieswithasymmetriesvirtuallyalladultssharethesameasymmetry,membersofthestarryflounderspeciescanbeeitherleft-eyed(botheyesontheleftsideofhead)orright-eyed.InthewatersbetweentheUnitedStatesandJapan,thestarryflounderpopulationsvaryfromabout50percentleft-eyedofftheUnitedStatesWestCoast,throughabout70percentleft-eyedhalfwaybetweentheUnitedStatesandJapan,tonearly100percentleft-eyedofftheJapanesecoast.

Biologistscallthiskindofgradualvariationoveracertaingeographicrangea“cline”andinterpretclinesasstrongindicationsthatthevariationisadaptive,aresponsetoenvironmentaldifferences.Forthestarryflounderthisinterpretationimpliesthatageometricdifference(betweenfishthataremirrorimagesofoneanother)isadaptive,thatleft-eyednessintheJapanesestarryflounderhasbeenselectedfor,whichprovokesaperplexingquestion:whatistheselectiveadvantageinhavingbotheyesononesideratherthanontheother?

Theeasewithwhichafishcanreversetheeffectofthesidednessofitseyeasymmetrysimplybyturningaroundhascausedbiologiststostudyinternalanatomy,especiallytheopticnerves,fortheanswer.Inallflatfishtheopticnervescross,sothattherightopticnerveisjoinedtothebrain’sleftsideandviceversa.Thiscrossingintroducesanasymmetry,asoneopticnervemustcrossaboveorbelowtheother.G.H.Parkerreasonedthatif,forexample,aflatfish’slefteyemigratedwhentherightopticnervewasontop,therewouldbeatwistingofnerves,whichmightbemechanicallydisadvantageous.Forstarryflounders,then,theleft-eyedvarietywouldbeselectedagainst,sinceinastarryfloundertheleftopticnerveisuppermost.

TheproblemwiththeaboveexplanationisthattheJapanesestarryflounderpopulationisalmostexclusivelyleft-eyed,andnaturalselectionneverpromotesapurelylessadvantageousvariation.Asotherexplanationsprovedequallyuntenable,biologistsconcludedthatthereisnoimportantadaptivedifferencebetweenleft-eyednessandright-eyedness,andthatthetwocharacteristicsaregeneticallyassociatedwithsomeotheradaptivelysignificantcharacteristic.Thissituationisonecommonlyencounteredbyevolutionarybiologists,whomustoftendecidewhetheracharacteristicisadaptiveorselectivelyneutral.Asfortheleft-eyedandright-eyedflatfish,theirdifference,howeverstriking,appearstobeanevolutionaryredherring.

1.Accordingtothetext,starryflounderdifferformmostotherspeciesofflatfishinthatstarryflounder

[A]arenotbasicallybilaterallysymmetric.

[B]donotbecomeasymmetricuntiladulthood.

[C]donotallsharethesameasymmetry.

[D]havebotheyesonthesamesideofthehead.

2.Whichofthefollowingbestdescribestheorganizationofthetextasawhole?

[A]Aphenomenonisdescribedandaninterpretationpresentedandrejected.

[B]Ageneralizationismadeandsupportingevidenceissuppliedandweighed.

[C]Acontradictionisnotedandaresolutionissuggestedandthenmodified.

[D]Aseriesofobservationsispresentedandexplainedintermsofthedominanttheory.

3.Thetextsuppliesinformationforansweringwhichofthefollowingquestions?

[A]WhyareJapanesestarryfloundermostlyleft-eyed?

[B]Whyshouldtheeye-sidednessinstarryflounderbeconsideredselectivelyneutral?

[C]Whyhavebiologistsrecentlybecomeinterestedinwhetheracharacteristicisadaptiveorselectivelyneutral?

[D]Howdotheeyesinflatfishmigrate?

4.Whichofthefollowingismostclearlysimilartoaclineasitisdescribedinthesecondparagraphofthetext?

[A]Avegetablemarketinwhichthevariousitemsaregroupedaccordingtoplaceoforigin.

[B]Awheatfieldinwhichdifferentvarietiesofwheatareplantedtoyieldacropthatwillbringthemaximumprofit.

[C]Aflowerstallinwhichthevariousspeciesofflowersarearrangedaccordingtotheirprice.

[D]Ahousingdevelopmentinwhichthelengthofthefrontstrutssupportingtheporchofeachhouseincreasesashousesarebuiltupthehill.

5.Whichofthefollowingphrasesfromthetextbestexpressestheauthor’sconclusionaboutthemeaningofthedifferencebetweenleft-eyedandright-eyedflatfish?

[A]“Moststriking”(line3,paragraph1)

[B]“variationisadaptive”(line2,paragraph2)

[C]“mechanicallydisadvantageous”(line7,paragraph3)

[D]“evolutionaryredherring”(line9,paragraph4)