SAMPLE 12
[生物学类]
Flatfish, such as the flounder, are among the few vertebrates that lack approximate bilateral symmetry . Most striking among the many asymmetries evident in an adult flatfish is eye placement: before maturity one eye migrates, so that in an adult flatfish both eyes are on the same side of the head. While in most species with asymmetries virtually all adults share the same asymmetry, members of the starry flounder species can be either left-eyed or right-eyed. In the waters between the United States and Japan, the starry flounder populations vary from about 50 percent left-eyed off the United States West Coast, through about 70 percent left-eyed halfway between the United States and Japan, to nearly 100 percent left-eyed off the Japanese coast.
Biologists call this kind of gradual variation over a certain geographic range a cline and interpret clines as strong indications that the variation is adaptive, a response to environmental differences. For the starry flounder this interpretation implies that a geometric difference is adaptive, that left-eyedness in the Japanese starry flounder has been selected for, which provokes a perplexing question: what is the selective advantage in having both eyes on one side rather than on the other?
The ease with which a fish can reverse the effect of the sidedness of its eye asymmetry simply by turning around has caused biologists to study internal anatomy, especially the optic nerves, for the answer. In all flatfish the optic nerves cross, so that the right optic nerve is joined to the brains left side and vice versa. This crossing introduces an asymmetry, as one optic nerve must cross above or below the other. G. H. Parker reasoned that if, for example, a flatfishs left eye migrated when the right optic nerve was on top, there would be a twisting of nerves, which might be mechanically disadvantageous. For starry flounders, then, the left-eyed variety would be selected against, since in a starry flounder the left optic nerve is uppermost.
The problem with the above explanation is that the Japanese starry flounder population is almost exclusively left-eyed, and natural selection never promotes a purely less advantageous variation. As other explanations proved equally untenable, biologists concluded that there is no important adaptive difference between left-eyedness and right-eyedness, and that the two characteristics are genetically associated with some other adaptively significant characteristic. This situation is one commonly encountered by evolutionary biologists, who must often decide whether a characteristic is adaptive or selectively neutral. As for the left-eyed and right-eyed flatfish, their difference, however striking, appears to be an evolutionary red herring.
1. According to the text, starry flounder differ form most other species of flatfish in that starry flounder
[A] are not basically bilaterally symmetric.
[B] do not become asymmetric until adulthood.
[C] do not all share the same asymmetry.
[D] have both eyes on the same side of the head.
2. Which of the following best describes the organization of the text as a whole?
[A] A phenomenon is described and an interpretation presented and rejected.
[B] A generalization is made and supporting evidence is supplied and weighed.
[C] A contradiction is noted and a resolution is suggested and then modified.
[D] A series of observations is presented and explained in terms of the dominant theory.
3. The text supplies information for answering which of the following questions?
[A] Why are Japanese starry flounder mostly left-eyed?
[B] Why should the eye-sidedness in starry flounder be considered selectively neutral?
[C] Why have biologists recently become interested in whether a characteristic is adaptive or selectively neutral?
[D] How do the eyes in flatfish migrate?
4. Which of the following is most clearly similar to a cline as it is described in the second paragraph of the text?
[A] A vegetable market in which the various items are grouped according to place of origin.
[B] A wheat field in which different varieties of wheat are planted to yield a crop that will bring the maximum profit.
[C] A flower stall in which the various species of flowers are arranged according to their price.
[D] A housing development in which the length of the front struts supporting the porch of each house increases as houses are built up the hill.
5. Which of the following phrases from the text best expresses the authors conclusion about the meaning of the difference between left-eyed and right-eyed flatfish?
[A] Most striking
[B] variation is adaptive
[C] mechanically disadvantageous
[D] evolutionary red herring
2016届高三英语二轮复习【专题三】形容词和副词(精品教学案)
2016届高考英语阅读改错提升训练29 资讯报道
2016届高考英语阅读改错提升训练32 经历感悟
2016届高中英语必备单词知识点(素材)重点词汇短语总结大全(上)
2016届高中英语短语知识点《Unit 1 Friendship》学案 新人教版必修1
2016届高中英语短语知识点《Unit 2 Healthy eating》学案 新人教版必修3
2016届高中英语必备单词知识点(素材)复习词组总结
2016届高三英语二轮复习【专题四】介词、连词与状语从句(精品教学案)
2016届高中英语短语知识点《Unit 3 Travel journal》学案 新人教版必修1
2016届高中英语必备单词知识点(素材)it用法考点聚焦
2016届高中英语必备单词知识点(素材)食品和用餐词汇
2016届高中英语短语知识点《Unit 1 Women of achievement》学案 新人教版必修4
2016届高三英语二轮复习【专题一】名词和代词(精品教学案)
2016届高中英语短语知识点《Unit 2 The Olympic Games》学案 新人教版必修2
2016届高考英语阅读改错提升训练34 健康饮食(阅读理解)
2016届高中英语必备单词知识点(素材)高中英语介词by的用法归纳总结
2016届高中英语必备单词知识点(素材)下册重点单词和短语知识点总结
2016届高中英语短语知识点《Unit 1 Cultural Relics》学案 新人教版必修2
2016届高中英语短语知识点《Unit 4 Astronomy the science of the stars》学案 新人教版必修3
Metonymy and synecdoche 修辞法:转喻和提喻
2016届高中英语必备单词知识点(素材)500多个高中英语重点词组总结
2016届高三英语二轮复习【专题二】冠词和代词(精品教学案)
2016届高中英语必备单词知识点(素材)关于方位的英语单词
2016届高三英语二轮复习【专题十】特殊句式与交际用语(精品教学案)
2016届高中英语必备单词知识点(素材)阅读高频词组总结
2016届高三英语二轮复习【专题七】情态动词与虚拟语气(精品教学案)
2016届高三英语二轮复习【专题六】非谓语动词(精品教学案)
2016届高中英语短语知识点《Unit 3 The Million Pound Bank Note》学案 新人教版必修3
2016届高中英语必备单词知识点(素材)有些英语词汇,不能不懂装懂
2016届高中英语必备单词知识点(素材)英语中常见的比喻词组
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |