首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the c
The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the c
admin
2011-02-26
62
问题
The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the cutter claw is long and slender. Such bilateral asymmetry, in which the right side of the body is, in all other respects, a mirror image of the left side, is not unlike handedness in humans. But where the majority of humans are right-handed, in lobsters the crusher claw appears with equal probability on either the right side or left side of the body.
Bilateral asymmetry of the claws comes about gradually. In the juvenile fourth and fifth stages of development, the paired claws are symmetrical and cutterlike. Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages. An intriguing aspect of this development was discovered by Victor Emmel. He found that if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher, while the regenerated claw becomes a cutter. Removal of a claw during a later juvenile stage or during adulthood, when asymmetry is present, does not alter the asymmetry; the intact and regenerate claws retain their original structures.
These observations indicate that the conditions that trigger differentiation must operate in a random manner when the paired claws are intact but in a nonrandom manner when one of the claws is lost. One possible explanation is that differential use of the claws determines their asymmetry. Perhaps the claw that is used more becomes the crusher. This would explain why, when one of the claws is missing during the fourth or fifth stage, the intact claw always becomes a crusher. With two intact claws, initial use of one claw might prompt the animal to use it more than the other throughout the juvenile fourth and fifth stages, causing it to become a crusher.
To test this hypothesis, researchers raised lobsters in the juvenile fourth and fifth stages of development in a laboratory environment in which the lobsters could manipulate oyster chips. (Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by borrowing in the substrate.) Under these conditions, the lobsters developed asymmetric claws, half with cutter claws on the left, and half with crusher claws on the right. In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws. This unusual configuration of symmetrical cutter claws did not change when the lobsters were subsequently placed in a manipulatable environment or when they lost and regenerated one or both claws.
Which of the following conditions does the passage suggest is a possible cause for the failure of a lobster to develop a crusher claw?
选项
A、The loss of a claw during the third or earlier stage of development.
B、The lose of claw during the fourth or fifth stage of development.
C、The loss of a claw during the sixth stage of development.
D、Development in an environment devoid of material that can be manipulated.
答案
D
解析
转载请注明原文地址:https://kaotiyun.com/show/njBO777K
0
考博英语
相关试题推荐
ReadthismemofromDingYuatyourcompany’sheadofficeinShanghai.MEMORANDUMFrom:DingYu,General
Youhaveorderedsomenewofficeequipment.However,someofthisequipmentwillarriveaweeklaterthanplanned.Writeamemo
AbriefhistoryoftheICTindustriesrevealsfourmainfacetsofdevelopment.First,inthetelecomindustry,China’srapiddev
•ReadthefollowingreviewofabookcalledNeverQuit!TheUpsandDownsofRunningaFamilyBusiness.•Foreachquestion
•Lookatthechartbelow.Itshowstheaveragesharepricesofeachmonthofthreecompaniesduringaneight-monthperiod.•
•Lookatthechartsbelow.Theyshowthenumberofdayslostbecauseofstaffabsenceineightcompanies,fromJunetoSeptember
•Lookatthelistbelow.Itshowsarticlesinabusinesswebsite.•Forquestions6-10,decidewhicharticle(A-H)eachperson
Hebecameawarethathehadlosthisaudiencesincehehadnotbeenabletotalk______aroundonetopic.
Americanliteraryhistoriansareperhaps______toviewingtheirownnationalscenetoonarrowly,mistakingprominenceforuniqu
Someoftheplan’sprovisionshavealreadyarousedopposition,mostnotablyfromPopeJohnPaulⅡ.
随机试题
简述国有土地有偿使用制度。
CharlesDickens______manywonderfulcharactersinhisnovels.
(2006年)级数内收敛于函数()。
下列关于客车出站的说法不正确的是()。
下列成本偏差的原因中,不属于业主原因的是()。
娱乐体育:人们在余暇时间进行的一种娱乐性极强的身体活动,它既是一种娱乐手段,又是一种身体锻炼的手段。下列不属于娱乐体育的一项是()。
改革要在________公平开放便利的市场环境上多下功夫,要在体恤民生上见真情。经济调整期,不能不顾小微企业的实际承受能力,无节制地追求税收增长率。一项不期而至的小微企业普惠型免税政策,是炎炎烈日中吹来的清凉之风,是充满温情和体恤的善政,从这个意义上说,这
【程序】SETTALKOFFI=1CLEARDOWHILEI<=2INPUT“A=”TOAIFA>INT(A).OR.A>=10LOOPELSEINPUT“B=”TO
In1608,Frenchexplorer,SamueldeChamplainestablishedhishabitationin
TheInternationalMonetaryFund(IMF)isthemostpowerfulfinancialinstitutionontheplanet,capableofdictatingeconomicpoli
最新回复
(
0
)