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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.
The passage provides information to support which of the following generalizations?
选项 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 likely to be higher when it is searching for prey than when it is evading predators.
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.
答案E
解析 文章支持下列哪个观点?A．动物生理行为在野外的观察除非得到了实验室验证，否则是不可靠的。正好说反，原文海豹的潜水生理机制实验室中的观测结果是不完全的，要用野外观测来修正。B．“less difficult to observe”文中未涉及观察难度。C．“lactic acid in an animal’s blood”暂且不论此观点用在海豹身上对不对，就是正确也不能推广到泛指任意一种动物。D．同C。E．正确。动物的野外生理行为并不总和实验室中一致。此结论只要能有一例，就可以说是“not always consistent”，文中海豹就是这样一个例子。
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