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  3. Studies of the Weddell seal in the laboratory have described the physiological mechanisms that allow the seal to cope with the e

Studies of the Weddell seal in the laboratory have described the physiological mechanisms that allow the seal to cope with the e

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问题     Studies of the Weddell seal in the laboratory have described the physiological mechanisms that allow the seal to cope with the extreme oxygen depriva- tion 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 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 blood stream. 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 oxy- gen 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 laborato- ry. 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 sub- merged, it does not know how long it will remain underwater and so prepares for the worst.
According to the author, which of the following is true of the laboratory studies mentioned in line 1 ?
选项 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.
答案E
解析 哪一个选项符合第1行中提到的实验室研究的叙述?A．不能解释在长时间潜水时怎样防止乳酸增多。恰恰相反，L24—34在实验室研究中说明解释了此问题。B．“an oversimplified account，”，从文中推不出来。C．提供证据削弱一观点：海豹在野外典型潜水中依靠无氧代谢。此现象恰恰是实验室研究所认可，而被以后的野外考察所推翻的。D．建立在一个假设上：海豹在野外很少潜水超过20分钟。说反了。不符合原文L6一8。E．正确。这些研究提供的解释对于海豹在野外探路或逃避追捕时生理行为是正确的。见原文L45—50。
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