大全 Passage29

小姣龙

Studies of the Weddell seal in the laboratory have described the physiological mechanisms that allow the seal to cope with the extreme oxygen deprivation that occurs during its longest dives, which can extend 500 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 physiological behavior is different.

In the laboratory, when the seal dives below the surface of the water and stops breathing, its heart beats more slowly, requiring less oxygen, and its arteries become constricted, ensuring that the seal’s blood remains concentrated near those organs most crucial to its ability to navigate underwater. The seal essentially shuts off the flow of blood to other organs, which either stop functioning until the seal surfaces or switch to an anaerobic (oxygen-independent) metabolism. The latter results in the production of large amounts of lactic acid (lactic acid: n.乳酸) which can adversely affect the pH of the seal’s blood, but since the anaerobic metabolism occurs only in those tissues which have been isolated 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 bloodstream.

Recent field studies, however, reveal that on dives in the wild, the seal usually heads directly for its prey and returns to the surface in less than twenty minutes. The absence of high levels of lactic acid in the seal’s blood 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 routes or evading a predator, do evoke 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 submerged, it does not know how long it will remain underwater and so prepares for the worst.

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）

(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.

我选了B，找不到原因

lukeleng

关于威德尔海豹特殊的生理机制，在实验室里对其进行的研究已作过描述。该生理机制使海豹可以适应长时间潜水时出现的极度缺氧。海豹长时间潜水时最深可达水面以下500米，时间可持续70多分钟。

实验室不同与野生状态． because in laboratory dives the seal is forcibly submerged,而在野生状态 是free diving－文章里没用这个词，文章说它不知道要在水下呆多久，就做了最坏的打算．

第二段对第一段however前面的句子进一步解释

[此贴子已经被作者于2008-2-3 8:12:30编辑过]

小姣龙

那么B有什么错误。。

还有个问题 就是是不是考试时候的阅读都要比63篇难很多阿。。

lukeleng

没考过，好像有个贴子说实战的短文会多些吧？每篇３至４题

Studies of the Weddell seal in the laboratory ，就是说在实验室里是这样．并没有就此推论在会在野生状态会怎样．野生状态是通过野外的研究得出结论的．

[此贴子已经被作者于2008-2-3 15:37:37编辑过]

小姣龙

实验室里的观察到的就是海豹在野外最长时间潜水的状态阿。。

lukeleng

Studies of the Weddell seal in the
                laboratory(实验室） have described the physiological mechanisms that allow the seal to cope with the extreme oxygen deprivation that occurs during its longest dives, which can extend 500 meters below the ocean’s surface and last for over 70 minutes. Recent field studies（实地）, however, suggest that during more typical dives in the wild, this seal’s physiological behavior is different.

In the laboratory(实验室） , when the seal dives below the surface of the water and stops breathing, its heart beats more slowly, requiring less oxygen, and its arteries become constricted, ensuring that the seal’s blood remains concentrated near those organs most crucial to its ability to navigate underwater. The seal essentially shuts off the flow of blood to other organs, which either stop functioning until the seal surfaces or switch to an anaerobic (oxygen-independent) metabolism. The latter results in the production of large amounts of lactic acid (lactic acid: n.乳酸) which can adversely affect the pH of the seal’s blood, but since the anaerobic metabolism occurs only in those tissues which have been isolated 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 bloodstream.

Recent field studies, however, reveal that on dives in the wild, the seal usually heads directly for its prey and returns to the surface in less than twenty minutes. The absence of high levels of lactic acid in the seal’s blood 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 routes or evading a predator, do evoke the diving response seen in the laboratory. But why do the seal’s laboratory dives (实验室）always evoke this response, regardless of their length or depth? Some biologists speculate that because in laboratory dives (实验室）the seal is forcibly submerged, it does not know how long it will remain underwater and so prepares for the worst.

[此贴子已经被作者于2008-2-4 7:30:51编辑过]