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 pes, which can extend 500meters below the oceans surface and last for over 70 minutes. Recent field studies, however, suggest that during more typical pes in the wild, this seals physiological behavior is different.
In the laboratory, when the seal pes below the surface of the water and sTOPs breathing, its heart beats more slowly, requiring less oxygen, and its arteries5 become constricted6, ensuring that the seals blood remains7 concentrated near those organs most crucial to its ability to navigate8 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 anaerobic9 metabolism10. The latter results in the production of large amounts of lactic11 acid which can adversely12 affect the pH of the seals blood but since the anaerobic metabolism occurs only in those tissues which have been isolated13 from the seals blood supply, the lactic acid is released into the seals blood only after the seal surfaces, when the lungs, liver, and other organs quickly clear the acid from the seals blood- stream.
Recent field studies, however, reveal that on pes 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 seals bloodafter such pes suggests that during them, the seals organs do not resort to the anaerobic metabolism observed in the laboratory, but are supplied with oxygen from the blood. The seals longer excursions underwater,during which it appears to be either exploring distant routes or evading15 a predator16, do evoke17 the ping response seen in the laboratory. But why do the seals laboratory pes always evoke this response, regardless of their length or depth? Some biologists speculate that because in laboratory pes the seal is forcibly 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?
Observations of animals physiological behavior in the wild are not reliable unless verified by laboratory studies.
It is generally less difficult to observe the physiological behavior of an animal in the wild than in the laboratory.
The level of lactic acid in an animals blood is likely to be higher when it is searching for prey than when it s evading predators19.
The level of lactic acid in an animals blood is likely to be lowest during those periods in which it experiences oxygen deprivation.
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 , biologists mean that it
prepares to remain underwater for no longer than twenty minutes
exhibits physiological behavior similar to that which characterizes pes in which it heads directly for its prey
exhibits physiological behavior similar to that which characterizes its longest pes in the wild.
begins to exhibit predatory behavior
clears the lactic acid from its blood before attempting to pe
3. The passage suggests that during laboratory pes, the pH of the Weddell seals blood is not adversely affected20 by the production of lactic acid because
only those organs that are essential to the seals ability to navigate underwater revert21 to an anaerobic mechanism2.
the seal typically reverts22 to an anaerobic metabolism only at the very end of the pe
organs that revert to an anaerobic metabolism are temporarily isolated from the seals bloodstream
oxygen continues to be supplied to organs that clear lactic acid from the seals bloodstream
the seal remains submerged for only short periods of time
4. Which of the following best summarizes the main point of the passage?
Recent field studies have indicated that descriptions of the physiological behavior of the Weddell seal during laboratory pes are not applicable to its most typical pes in the wild.
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.
The results of recent field studies have made it necessary for biologists to revise previous perceptions of how the Weddell seal behaves physiologically23 during its longest pes in the wild.
Biologists speculate that laboratory studies of the physiological behavior of seals during pes lasting24 more than twenty minutes would be more accurate if the seals were not forcibly submerged.
How the Weddell seal responds to oxygen deprivation during its longest pes appears to depend on whether the seal is searching for prey or avoiding predators during such pes.
5. According to the author, which of the following is true of the laboratory studies mentioned in line 1 ?
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 pes in the wild.
They present an oversimplified account of mechanisms that the Weddell seal relies on during its longest pes in the wild.
They provide evidence that undermines the view that the Weddell seal relies on an anaerobic metabolism during its most typical pes in the wild.
They are based on the assumption that Weddell seals rarely spend more than twenty minutes underwater on a typical pe in the wild.
They provide an accurate account of the physiological behavior of Weddell seals during those pes 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 seals physiological behavior during pes observed in the laboratory?
Ⅰ. A decrease in the rate at which the seals heart beats
Ⅱ. A constriction25 of the seals arteries
Ⅲ. A decrease in the levels of lactic acid in the seals blood
Ⅳ. A temporary halt in the functioning of certain organs
Ⅰand Ⅲ only
Ⅱ and Ⅳ only
Ⅱ and Ⅲ only
Ⅰ,Ⅱ, and Ⅳ only
Ⅰ,Ⅲ, and Ⅳ only
7. The passage suggests that because Weddell seals are forcibly submerged during laboratory pes, they do which of the following?
Exhibit the physiological responses that are characteristic of pes in the wild that last less than twenty minutes.
Exhibit the physiological responses that are characteristic of the longer pes they undertake in the wild.
Cope with oxygen deprivation less effectively than they do on typical pes in the wild.
Produce smaller amounts of lactic acid than they do on typical pes in the wild.
Navigate less effectively than they do on typical pes in the wild
