首页
登录
职称英语
The two claws of the mature American lobster are decidedly different from eac
The two claws of the mature American lobster are decidedly different from eac
游客
2025-04-13
28
管理
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 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 cutter like. Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crasher 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 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, haft 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 manipulatable environment or when they lost and regenerated one or both claws. [br] Which of the following experimental results, if observed, would most clearly contradict the findings of Victor Emmet?
选项
A、A left cutter like claw is removed in the fifth stage and a crusher claw develops on the right side.
B、A left cutter like claw is removed in the fourth stage and a crusher claw develops on the left side.
C、A left cutter like claw is removed in the six stage and a crusher-claw develops on the fight side.
D、A left cutter like claw is removed in the fourth stage and a crusher claw develops on the right side.
答案
B
解析
Victor Emmerg的发现是:如果在龙虾生长的第四或第五期弄掉它一只角的话,那么完好的那一只角就会成为crusher claw,而再生的就会成为cutter claw。但如果这发生在这一生长期之后,那么龙虾的已有结构就不会改变了。而B是与这一发现相违背的。所以正确答案为B。
转载请注明原文地址:https://tihaiku.com/zcyy/4036513.html
相关试题推荐
TheBritishhistorianNiallFergusonspeculatedthattheendofAmerican______m
TheroleofAmericanwomen______significantlyfromthetimethenationwasborn,
InAmericanuniversities,classesareoftenarrangedinmoreflexible______andm
ThenewtechnologicalrevolutioninAmericannewspapershasbroughtincreased___
Morethantwopartiesindifferentlocationscantalk______viaaconferencecall
GeorgeWashington______.A、alwayswillandalwayshasbeenanAmericanheroB、alw
Thesystemhasadifferentmoralityasagroupthanthepeopledoasindividuals
SometimesAmericansaresaidtobe______.Perhapsitseemsso,buttheyareprob
Inthepast,Americancollegesanduniversitieswerecreatedtoserveadual
Inthepast,Americancollegesanduniversitieswerecreatedtoserveadual
随机试题
WheredoesJanework?[br][originaltext]M:Howisyourjobdoing,Jane?W:Gr
ThefirsttimeIleftmymother,Iwasfiveyearsold.ShetoldmeIcouldn’
Airportclerk:CanIhaveyourticket,please?Passenger:______A、Yes,ofcours
4世纪时,北非发生了(),动摇了罗马在北非的统治。A.巴贝克起义 B.“阿哥
安全阀的优点是()。A.用于受压设备、容器和道路上,当压力超过规定数值时,能
A.红细胞 B.淋巴细胞 C.血小板 D.粒细胞
根据所给图形的既有规律,选出一个最合理的答案。( ) A、A B、B C
无风险利率水平会影响期权的()。A.时间价值 B.空间价值 C.内涵价值
关于咀嚼的功能不正确A.咀嚼食物是消化过程的第一步,食物进入口腔,经过上下牙对食
根据规定,被取消公益性捐赠税前扣除资格的公益性群众团体,()年内不得重新申请公
最新回复
(
0
)