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
2011-05-29
49
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 fight 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 crasher 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 cutter like. 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 Emmer. 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 crusher 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 ma nipulable environment or when they lost and regenerated one or both claws.
The passage is primarily concerned with ______ .
选项
A、drawing an analogy between asymmetry in lobsters and handedness in humans
B、developing a method for predicating whether crusher claws in lobster will appear on the left or right side
C、explaining differences between lobsters’ crusher claws and cutter claws
D、discussing a possible explanation for the way bilateral asymmetry is determined in lobsters
答案
D
解析
本题的四个选项中,只有D项为正确答案。这可从文中的内容推知,即本文都是围绕龙虾不对称螯的形成原因展开讨论,科学家们试图通过试验向人们解释这一现象。
转载请注明原文地址:https://kaotiyun.com/show/9j6O777K
0
考博英语
相关试题推荐
Questions41-45•Readthememoandtheemailbelow.•Completetheform.•Writeawordorphrase(inCAPITALLETTERS)oranum
Readthefollowingminutesofameeting.Aresentences16-22ontheoppositepage’Right’or’Wrong’?Ifthereisnotenough
•Readthearticleaboutthefutureoftheairlineindustry.•Choosethebestwordtofillineachgap,fromA,BorC.•Fore
Lookatthegraphsbelow.Theyshowtheclosingsharepricesattheendofeachday’stradingofeightdifferentcompaniesfrom
MEMOTo:AllStaffFrom:EuniceLaneDate:15June2009Subject:StaffTrainingProgrammeTwochoicesareavailablefortheStaf
Readthearticlebelowaboutmanagingchangeatabank.Aresentences16-22ontheoppositepage’Right’or’Wrong’?Ifthere
ItisnotoftenrealizedthatwomenheldahighplaceinsouthernEuropeansocietiesinthe10thand11thcenturies.Asawife,
TheUnitedStateswastryinghardtosmoketheenemyoutoftheholesinthetargetcountry.
Theprocessbymeansofwhichhumanbeingsarbitrarilymakecertainthingsstandforotherthingsmaybecalledthesymbolicpro
Hurricanesareviolentstormsthatcausemillionsofdollarsinpropertydamageandtakemanylives.Theycanbeextremelydange
随机试题
甲、乙、丙、丁四人出资设立A有限合伙企业(以下简称“A企业”),其中甲、乙为普通合伙人,丙、丁为有限合伙人。合伙企业存续期间,发生以下事项:(1)5月,合伙人丙同A企业进行了120万元的交易,合伙人甲认为,由于合伙协议对此没有约定,因此,有限合伙人丙不得
Idon’tknowwhysheavoids________heropiniononthesubject.
电能表的总线应用铜芯绝缘线,其最小截面规定为________mm2。
团队沟通
用回弹法检验水泥混凝土的强度,需测出碳化深度,当用1%酚酞酒精溶液滴在孔的内壁,发现该混凝土已碳化,碳化后的颜色是()。
某旧建筑物,其建造成本为45万元,重置成本为48万元,墙、地面破旧折旧为8万元,户型不好导致功能折旧为9万元,区位变化引起的经济折旧为5万元,则该建筑物现值为()万元。
案例五:李先生打算为刚上小学的儿子筹备大一的开支。他准备采用教育储蓄的方式进行。为此,他向理财规划师咨询有关问题。根据案例五,回答下列问题:利用教育储蓄的最长期限,李先生应当在他儿子( )时开立教育储蓄账户。
预先披露的招股说明书(申报稿)不是发行人发行股票的正式文件,不能含有(),发行人不得据此发行股票。
下列事项中,属于会计估计变更的是()。
Whichofthefollowingdoesthefirstparagraphimply?Whatdoestheauthorconclude?
最新回复
(
0
)