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
52
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.
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
本题的四个选项中,只有D项为正确答案。这可从文中的最后两句话“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 manipulable environment or when they lost and regenerated one or both claws. ”推知,即在没有可以操作的对象的环境中长大的龙虾是不会长出crusher claw的。
转载请注明原文地址:https://kaotiyun.com/show/Bj6O777K
0
考博英语
相关试题推荐
FINANCEDEPARTMENTRELOCATIONFriday’smeetingiscompulsoryforallFinancestaff;otherswelcometoattendforinformation.
•Readthearticleaboutthefutureoftheairlineindustry.•Choosethebestwordtofillineachgap,fromA,BorC.•Fore
ReadthefollowingreviewsofabookcalledTheBossesSpeak.Foreachquestion23-28,choosethecorrectanswer.Markletter
AirlineTravelInmostcases,thecompanywillmakeairtravelarrangements.Bepreparedtochargeyourticket(usingacredi
Whetheryouwantaccesstoalltheday’snewsfast,breakinganalysisoftheevents,aconsideredviewoftrends,expertcomment
Lookatthechartsbelow.Theyshowamanufacturingcompany’sproductionlevels,thenumberofstaffinitsproductiondepartmen
MATRIX:NUMBERS
Theprocessbymeansofwhichhumanbeingsarbitrarilymakecertainthingsstandforotherthingsmaybecalledthesymbolicpro
Itwas(andis)commontothinkthatotheranimalsareruledby"instinct"whereashumanslosttheirinstinctsandruledby"rea
Hurricanesareviolentstormsthatcausemillionsofdollarsinpropertydamageandtakemanylives.Theycanbeextremelydange
随机试题
A—fluorescentlampJ—microwaveovenB—electricfanK—smokeexhausterC—dictatingmachine
酸中毒患者肾排碱性尿液可见于
女性,50岁,长期从事文书编辑工作,颈部疼痛及僵硬,短期内加重向肩部及上肢放射。用力咳嗽、打喷嚏及颈部活动时,疼痛加重。皮肤可有麻木、过敏等感觉改变。上肢肌力下降,手指动作不灵活。头部偏向患侧。颈肩部有局限性压痛,活动受限。上肢牵拉试验阳性。颈椎X线片可见
有抗组胺作用和较强的中枢抑制作用的药是抗组胺作用较强用量少,与解热镇痛药配伍用于治疗感冒
A.矫味剂B.遮光剂C.防腐剂D.增塑剂E.抗氧剂在包制薄膜衣的过程中,所加入的二氧化钛是
下列属于商业银行客户风险内生变量中实力类指标的是()。
()创作方法是指艺术家以奔放的主观激情,按照理想的面貌去表现生活的艺术创作方法。
Theideathatsomegroupsofpeoplemaybemoreintelligentthanothersisoneofthosehypothesesthatdarenotspeakitsname.
设有窗体的FormMouseMove事件过程如下:PrivateSubForm_MouseMove(ButtonAsInteger,ShiftAsInteger,XAsSingle,YAsSingle)If(ButtonAnd3
打开考生文件夹下的演示文稿yswg.pptx,按照下列要求完成对此文稿的修饰并保存。1.使用“精装15”主题修饰全文,全部幻灯片切换方案为“蜂巢”。2.第二张幻灯片前插入版式为“两栏内容”的新幻灯片,将第_三张幻灯片的标题移到第二张幻
最新回复
(
0
)