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
2021-06-15
22
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.
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
本题的四个选项中,只有A项为正确答案。这可从文中最后一段的内容推知,即龙虾螯不对称的形成是在第四和第五期,因为这时期龙虾的生活环境发生改变,它们开始使用螯工作,而在这之前它们只是在被动地随波逐流。
转载请注明原文地址:https://kaotiyun.com/show/gDTO777K
0
考博英语
相关试题推荐
HerofficeintheFirstNationalBankbuildingisprovisional.
Thisorganizationisalsoamanufacturingfirm.Here,however,managementencouragesandrewardsrisktakingandchange.Decisio
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand
"Before,weweretooblacktobewhite.Now,we’retoowhitetobeblack."Hadija,oneofSouthAfrica’s3.5mColoured(mixedr
Thedevelopmentofwritingwasoneofthegreathumaninventions.Itisdifficult【C1】______manypeopletoimaginelanguagewitho
Ihaveheardmanydifferent______ofthesamestory.
Thisyearthefarmerswerejustabletogatherinthe______beforethefineweathercametoanend.
UnderethicalguidelinerecentlyadoptedbytheNationalInstitutesofHealth,humangenesaretobemanipulatedonlytocorrect
Inhiswillhelefta(n)______ofoveronemilliondollarstobedividedamonghischildren.
Thecompanywill______toitsagreement,nomatterhowcostlytheprocessmaybe.(2002年中国人民大学考博试题)
随机试题
髋关节后脱位的复位手法不包括
(本小题可以选用中文或英文解答)A公司是一家在上交所上市的公司。该公司2018年度利润分配以及资本公积转增股本实施公告中披露的分配方案主要信息为:每10股送6股派发现金股利2元,以资本公积每10股转增4股。该公司在实施利润分配前,所有者权益情况如下:单位
为了消除腐败,实行处级以上干部岗位轮换制度,规定同一岗位工作不得超过5个。这种做法属于()控制。
通常所说的I/O设备指的是______________。
动物血管内严重溶血时最易导致
居民因房屋征收重新购置的住房,购房成交价与征收补偿款等额部分免征契税。()
下列股票交易行为中,不违反证券法律制度规定的是()。
一般的书刊印制过程中,图文处理是()必不可少的一个环节。
根据下面资料回答86~90题对全国31个省(区、市)6.8万户农村住户的抽样调查结果显示,2008年一季度农村居民人均现金收入1494元,同比增长18.5%,扣除价格因素,实际增长9.1%,增速比上年同期下降3个百分点。农民的工资性收入人均60
根据我国《专利法》的有关规定,下列表述正确的是()。
最新回复
(
0
)