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
68
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.
It can be inferred from the passage that one difference between lobsters in the earlier stages of development and those in the juvenile fourth and fifth stages is that lobsters in the early stages are ______.
选项
A、likely to be less active
B、likely to be less symmetrical
C、more likely to replace a crusher claw with a cutter claw.
D、more likely to regenerate a lost claw
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/9jBO777K
0
考博英语
相关试题推荐
YouareanemployeeofHumanResourcesDepartmentandareworkingontheholidayscheduleforOctober.Writeamemotoalldepar
TradingPlacesWendyLedgerlooksatjobswapping,astaffdevelopmentschemeinwhichemployeesexchangejobsforashort
•Readthearticlebelowaboutworkingindifferentsizedcompanies.•Aresentences16-22ontheoppositepage’Right’or’Wrong’
•Lookatthechartsbelow.Theyshowthenumberofdayslostbecauseofstaffabsenceineightcompanies,fromJunetoSeptember
•Readtheatriclebelowabouttheneedofemployees.•ChoosethecorrectwordtofilleachgapfrOmA.BorContheopposit
•Lookatthenoticebelow,whichshowsthedifferentdivisionsofamanufacturingcompany.•Forquestions11-15,decidewher
Warning:NibbletreatBiscuitsPacketsofthisproductdated01-30Junehavebeenwithdrawnforhealthreasons.Forarefund,b
Theeffectofthebabyboomontheschoolshelpedtomakepossibleashiftinthinkingabouttheroleofpubliceducationinthe
Smithfailedto______forthedeficitinthecompany’sbankbalance.
Improvementsinlaborproductivity【C1】______increasewagesandsalaries.Wagesandsalaries【C2】______about75percentofall
随机试题
设则f(x)在(一∞,+∞)内().
《像山那样思考》选自()
构成心瓣膜的结构是
照片影像失真度的概念,正确的是
胎儿出生时体内贮存铁为
在某县法院审理郑某盗窃案过程中,检察机关发现本案被告人郑某不仅有起诉书所指控的两起盗窃行为,而且涉嫌另两起盗窃案件。为此,检察机关要求延期审理,以便对此进行补充侦查。本案的补充侦查应以下列哪种方式进行?()
按照报关的目的不同,报关可以分为()。
蒲松龄是我国清代著名的文学家,别号五柳居士。()
A是3阶矩阵,有特征值λ1=λ2=2,对应两个线性无关的特征向量为ξ1,ξ2,ξ3=-2对应的特征向量是ξ3.(I)问ξ1﹢ξ2是否是A的特征向量?说明理由;(Ⅱ)问ξ2﹢ξ3是否是A的特征向量?说明理由;(Ⅲ)证明任意3维非零向量β都是A2的特征向
AMALDEXLIMITEDBriefingnotesforStaffonParkHotelConferenceArrangementsforStaff:1.Staffcanparkinthecarparkloca
最新回复
(
0
)