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Passage 29
  Studies of the Weddell seal in the laboratory have described the physiological1 mechanisms3 that allow the seal to cope with the extreme oxygen deprivation4 that occurs during its longest dives, which can extend 500(5) meters below the ocean‘s surface and last for over 70 minutes. Recent field studies, however, suggest that during more typical dives in the wild, this seal’s physio-logical behavior is different.
  In the laboratory, when the seal dives below the(10) surface of the water and stops breathing, its heart beats  more slowly, requiring less oxygen, and its arteries5 become constricted6, ensuring that the seal‘s blood  remains7 concentrated near those organs most crucial to its ability to navigate8 underwater. The seal essentially(15) shuts off the flow of blood to other organs, which either stop functioning until the seal surfaces or switch to an  anaerobic9 (oxygen-independent) metabolism10. The latter results in the production of large amounts of lactic11 acidwhich can adversely12 affect the pH of the seal’s blood(20) but since the anaerobic metabolism occurs only in those tissues which have been isolated13 from the seal‘s blood supply, the lactic acid is released into the seal’s blood only after the seal surfaces, when the lungs, liver, and other organs quickly clear the acid from the seal‘s blood-(25) stream.
  Recent field studies, however, reveal that on dives in the wild, the seal usually heads directly for its prey14 and returns to the surface in less than twenty minutes. The absence of high levels of lactic acid in the seal‘s blood(30) after such dives suggests that during them, the seal’s organs do not resort to the anaerobic metabolism observed in the laboratory, but are supplied with oxygen from the blood. The seal‘s longer excursions underwater,during which it appears to be either exploring distant(35) routes or evading15 a predator16, do evoke17 the diving response seen in the laboratory. But why do the seal’s laboratory dives always evoke this response, regardless of their length or depth? Some biologists speculate that because in laboratory dives the seal is forcibly(40) submerged, it does not know how long it will remain underwater and so prepares for the worst.

  1. The passage provides information to support which of the following generalizations18
   (A) Observations of animals‘ physiological behavior in the wild are not reliable unless verified by laboratory studies.
   (B) It is generally less difficult to observe the physiological behavior of an animal in the wild than in the laboratory.
   (C) The level of lactic acid in an animal‘s blood is likelyto be higher when it is searching for prey than whenit s evading predators19.
   (D) The level of lactic acid in an animal‘s blood is likely to be lowest during those periods in which it experiences oxygen deprivation.
   (E) The physiological behavior of animals in a laboratory setting is not always consistent with their physiological behavior in the wild.

  2. It can be inferred from the passage that by describing the Weddell seal as preparing “for the worst” (line 41), biologists mean that it
   (A) prepares to remain underwater for no longer than twenty minutes
   (B) exhibits physiological behavior similar to that which characterizes dives in which it heads directly for its prey
   (C) exhibits physiological behavior similar to that which characterizes its longest dives in the wild.
   (D) begins to exhibit predatory behavior
   (E) clears the lactic acid from its blood before attempting to dive

  3. The passage suggests that during laboratory dives, the pH of the Weddell seal‘s blood is not adversely affected20 by the production of lactic acid because
   (A) only those organs that are essential to the seal‘s ability to navigate underwater revert21 to an anaerobic mechanism2.
   (B) the seal typically reverts22 to an anaerobic metabolism only at the very end of the dive
   (C) organs that revert to an anaerobic metabolism aretemporarily isolated from the seal‘s bloodstream
   (D) oxygen continues to be supplied to organs that clear lactic acid from the seal‘s bloodstream
   (E) the seal remains submerged for only short periods of time

  4. Which of the following best summarizes the main point of the passage?
   (A) Recent field studies have indicated that descriptions of the physiological behavior of the Weddell sealduring laboratory dives are not applicable to its mosttypical dives in the wild.
   (B) The Weddell seal has developed a number of unique mechanisms that enable it to remain submerged at depths of up to 500 meters for up to 70 minutes.
   (C) The results of recent field studies have made it necessary for biologists to revise previousperceptions of how the Weddell seal behavesphysiologically during its longest dives in the wild.
   (D) Biologists speculate that laboratory studies of the physiological behavior of seals during dives lastingmore than twenty minutes would be more accurate ifthe seals were not forcibly submerged.
   (E) How the Weddell seal responds to oxygen deprivation during its longest dives appears to depend on whether the seal is searching for prey or avoiding predators during such dives.

  5. According to the author, which of the following is true of the laboratory studies mentioned in line 1 ?
   (A) They fail to explain how the seal is able to tolerate the increased production of lactic acid by organs that revert to an anaerobic metabolism during its longest dives in the wild.
   (B) They present an oversimplified account of mechanisms that the Weddell seal relies on during its longest dives in the wild.
   (C) They provide evidence that undermines the view that the Weddell seal relies on an anaerobic metabolism during its most typical dives in the wild.
   (D) They are based on the assumption that Weddell seals rarely spend more than twenty minutes underwater   on a typical dive in the wild.
   (E) They provide an accurate account of the physiological behavior of Weddell seals during those dives in the wild in which they are either  evading predators or exploring distant routes.

  6. The author cites which of the following as characteristic of the Weddell seal‘s physiological behavior during  dives observed in the laboratory?
   Ⅰ. A decrease in the rate at which the seal‘s heart beats
   Ⅱ. A constriction23 of the seal‘s arteries
   Ⅲ. A decrease in the levels of lactic acid in the seal‘s blood 
   Ⅳ. A temporary halt in the functioning of certain organs
   (A) Ⅰand Ⅲ only
   (B) Ⅱ and Ⅳ only
   (C) Ⅱ and Ⅲ only
   (D) Ⅰ,Ⅱ, and Ⅳ only
   (E) Ⅰ,Ⅲ, and Ⅳ only

  7. The passage suggests that because Weddell seals are forcibly submerged during laboratory dives, they do which of the following?
   (A) Exhibit the physiological responses that are characteristic of dives in the wild that last less than twenty minutes.
   (B) Exhibit the physiological responses that are characteristic of the longer dives they undertake in the wild.
   (C) Cope with oxygen deprivation less effectively than they do on typical dives in the wild.
   (D) Produce smaller amounts of lactic acid than they do on typical dives in the wild.
   (E) Navigate less effectively than they do on typical dives in the wild


1 physiological aAvyK     
  • He bought a physiological book.他买了一本生理学方面的书。
  • Every individual has a physiological requirement for each nutrient.每个人对每种营养成分都有一种生理上的需要。
2 mechanism zCWxr     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
3 mechanisms d0db71d70348ef1c49f05f59097917b8     
n.机械( mechanism的名词复数 );机械装置;[生物学] 机制;机械作用
  • The research will provide direct insight into molecular mechanisms. 这项研究将使人能够直接地了解分子的机理。 来自《简明英汉词典》
  • He explained how the two mechanisms worked. 他解释这两台机械装置是如何工作的。 来自《简明英汉词典》
4 deprivation e9Uy7     
  • Many studies make it clear that sleep deprivation is dangerous.多实验都证实了睡眠被剥夺是危险的。
  • Missing the holiday was a great deprivation.错过假日是极大的损失。
5 arteries 821b60db0d5e4edc87fdf5fc263ba3f5     
n.动脉( artery的名词复数 );干线,要道
  • Even grafting new blood vessels in place of the diseased coronary arteries has been tried. 甚至移植新血管代替不健康的冠状动脉的方法都已经试过。 来自《简明英汉词典》
  • This is the place where the three main arteries of West London traffic met. 这就是伦敦西部三条主要交通干线的交汇处。 来自《简明英汉词典》
6 constricted 6e98bde22e7cf0105ee4310e8c4e84cc     
  • Her throat constricted and she swallowed hard. 她喉咙发紧,使劲地咽了一下唾沫。
  • The tight collar constricted his neck. 紧领子勒着他的脖子。
7 remains 1kMzTy     
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
8 navigate 4Gyxu     
  • He was the first man to navigate the Atlantic by air.他是第一个飞越大西洋的人。
  • Such boats can navigate on the Nile.这种船可以在尼罗河上航行。
9 anaerobic BLzyN     
  • Anaerobic respiration occurs only in particularly active tissues such as muscles during severe exercise. 厌氧呼吸只有在处于剧烈运动状态的肌肉等特别活跃的组织中才会发生。
  • Infection,especially anaerobic infection, is much more apt to occur.感染,特别是厌氧感染很容易发生。
10 metabolism 171zC     
  • After years of dieting,Carol's metabolism was completely out of whack.经过数年的节食,卡罗尔的新陈代谢完全紊乱了。
  • All living matter undergoes a process of metabolism.生物都有新陈代谢。
11 lactic t2Cx6     
  • Now they wear rubber fingers treated with lactic acid.现在他们带上了用乳酸处理过的橡皮指套。
  • Lactic acid is an important organic acid of industrial importance.乳酸是一种具有重要工业价值的有机酸。
12 adversely 6zEzi6     
  • We commented adversely upon the imbecility of that message of telegraphic style. 我们对着这条电报式的愚蠢的留言发泄了一通不满。
  • Widely fluctuating exchange rates may adversely affect international trade. 浮动幅度很大的汇率可能会对国际贸易产生有害的影响。
13 isolated bqmzTd     
  • His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
  • Patients with the disease should be isolated. 这种病的患者应予以隔离。
14 prey g1czH     
  • Stronger animals prey on weaker ones.弱肉强食。
  • The lion was hunting for its prey.狮子在寻找猎物。
15 evading 6af7bd759f5505efaee3e9c7803918e5     
逃避( evade的现在分词 ); 避开; 回避; 想不出
  • Segmentation of a project is one means of evading NEPA. 把某一工程进行分割,是回避《国家环境政策法》的一种手段。 来自英汉非文学 - 环境法 - 环境法
  • Too many companies, she says, are evading the issue. 她说太多公司都在回避这个问题。
16 predator 11vza     
  • The final part of this chapter was devoted to a brief summary of predator species.本章最后部分简要总结了食肉动物。
  • Komodo dragon is the largest living lizard and a fearsome predator.科摩多龙是目前存在的最大蜥蜴,它是一种令人恐惧的捕食性动物。
17 evoke NnDxB     
  • These images are likely to evoke a strong response in the viewer.这些图像可能会在观众中产生强烈反响。
  • Her only resource was the sympathy she could evoke.她以凭借的唯一力量就是她能从人们心底里激起的同情。
18 generalizations 6a32b82d344d5f1487aee703a39bb639     
一般化( generalization的名词复数 ); 普通化; 归纳; 概论
  • But Pearlson cautions that the findings are simply generalizations. 但是波尔森提醒人们,这些发现是简单的综合资料。 来自英汉非文学 - 生命科学 - 大脑与疾病
  • They were of great service in correcting my jejune generalizations. 他们纠正了我不成熟的泛泛之论,帮了我大忙。
19 predators 48b965855934a5395e409c1112d94f63     
n.食肉动物( predator的名词复数 );奴役他人者(尤指在财务或性关系方面)
  • birds and their earthbound predators 鸟和地面上捕食它们的动物
  • The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》
20 affected TzUzg0     
  • She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
  • His manners are affected.他的态度不自然。
21 revert OBwzV     
  • Let us revert to the earlier part of the chapter.让我们回到本章的前面部分。
  • Shall we revert to the matter we talked about yesterday?我们接着昨天谈过的问题谈,好吗?
22 reverts 7f5ab997720046a2d88de6e7d721c519     
恢复( revert的第三人称单数 ); 重提; 回到…上; 归还
  • The mind reverts to the earliest days of colonial history. 我们回想到早期的殖民地历史。
  • Macau reverts to Chinese sovereignty at midnight on December19. 澳门主权于十二月十九日零时回归中国。
23 constriction 4276b5a2f7f62e30ccb7591923343bd2     
压缩; 紧压的感觉; 束紧; 压缩物
  • She feels a constriction in the chest. 她胸部有压迫感。
  • If you strain to run fast, you start coughing and feel a constriction in the chest. 还是别跑紧了,一咬牙就咳嗽,心口窝辣蒿蒿的! 来自汉英文学 - 骆驼祥子