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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
(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 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
(15) 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
(20) 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-
(25) 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
(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 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
(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 generalizations?
(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 s 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.
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
affected by the
production of lactic acid because
(A) only those organs that are essential to the seal’s
ability to navigate underwater revert to an anaerobic
mechanism.
(B) the seal typically reverts to an anaerobic metabolism
only at the very end of the dive
(C) organs that revert to an anaerobic metabolism are
temporarily 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 seal
during laboratory dives are not applicable to its most
typical 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 previous
perceptions of how the Weddell seal behaves
physiologically during its longest dives in the wild.
(D) Biologists speculate that laboratory studies of the
physiological behavior of seals during dives lasting
more than twenty minutes would be more accurate if
the 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 constriction 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