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蛇是不是这篇：
In terrestrial environments, gravity places
special demands on the cardiovascular systems of
animals. Gravitational pressure can cause blood to
pool in the lower regions of the body, making it
difficult to circulate blood to critical organs such as
the brain. Terrestrial snakes, in particular, exhibit
adaptations that aid in circulating blood against the
force of gravity.
The problem confronting terrestrial snakes is best
illustrated by what happens to sea snakes when
removed from their supportive medium. Because the
vertical pressure gradients within the blood vessels
are counteracted by similar pressure gradients in
the surrounding water, the distribution of blood
throughout the body of sea snakes remains about
the same regardless of their orientation in space,
provided they remain in the ocean. When removed
from the water and tilted at various angles with the
head up, however, blood pressure at their midpoint
drops significantly, and at brain level falls to zero.
That many terrestrial snakes in similar spatial
orientations do not experience this kind of circulatory
failure suggests that certain adaptations enable them
to regulate blood pressure more effectively in those
orientations.
One such adaptation is the closer proximity of the
terrestrial snake's heart to its head, which helps to
ensure circulation to the brain, regardless of the
snake’s orientation in space. The heart of sea snakes
can be located near the middle of the body, a
position that minimizes the work entailed in
circulating blood to both extremities. In arboreal
snakes, however, which dwell in trees and often
assume a vertical posture, the average distance
from the heart to the head can be as little as
15 percent of overall body length. Such a location
requires that blood circulated to the tail of the
snake travel a greater distance back to the heart,
a problem solved by another adaptation. When
climbing, arboreal snakes often pause
momentarily to wiggle their bodies, causing waves
of muscle contraction that advance from the lower
torso to the head. By compressing the veins and
forcing blood forward, these contractions
apparently improve the flow of venous blood
returning to the heart.
The passage provides information in support of which of the following
assertions?
(A) The disadvantages of an adaptation to a particular feature of an environment
often outweigh the advantages of such an adaptation.
(B) An organism's reaction to being placed in an environment to which it is not
well adapted can sometimes illustrate the problems that have been solved by the
adaptations of organisms indigenous to that environment.
(C) The effectiveness of an organism's adaptation to a particular feature of its
environment can only be evaluated by examining the effectiveness with which
organisms of other species have adapted to a similar feature of a different
environment.
(D) Organisms of the same species that inhabit strikingly different environments
will often adapt in remarkably similar ways to the few features of those
environments that are common.
(E) Different species of organisms living in the same environment will seldom
adapt to features of that environment in the same way.
Answer: B
According to the passage, one reason that the distribution of blood in the sea
snake changes little while the creature remains in the ocean is that
(A) the heart of the sea snake tends to be located near the center of its body
(B) pressure gradients in the water surrounding the sea snake counter the effects
of vertical pressure gradients within its blood vessels
(C) the sea snake assumes a vertical posture less frequently than do the
terrestrial and the arboreal snake
(D) the sea snake often relies on waves of muscle contractions to help move blood
from the torso to the head
(E) the force of pressure gradients in the water surrounding the sea snake
exceeds that of vertical pressure gradients within its circulatory system
Answer: B
It can be inferred from the passage that which of the following is true of
species of terrestrial snakes that often need to assume a vertical posture?
(A) They are more likely to be susceptible to circulatory failure in vertical
postures than are sea snakes.
(B) Their hearts are less likely to be located at the midpoint of their bodies than
is the case with sea snakes.
(C) They cannot counteract the pooling of blood in lower regions of their bodies
as effectively as sea snakes can.
(D) The blood pressure at their midpoint decreases significantly when they are
tilted with their heads up.
(E) They are unable to rely on muscle contractions to move venous blood from the
lower torso to the head.
Answer: B
The author describes the behavior of the circulatory system of sea snakes
when they are removed from the ocean (see lines 17-20) primarily in order to
(A) illustrate what would occur in the circulatory system of terrestrial snakes
without adaptations that enable them to regulate their blood pressure in vertical
orientations
(B) explain why arboreal snakes in vertical orientations must rely on muscle
contractions to restore blood pressure to the brain
(C) illustrate the effects of circulatory failure on the behavior of arboreal snakes
(D) illustrate the superiority of the circulatory system of the terrestrial snake to
that of the sea snake
(E) explain how changes in spatial orientation can adversely affect the circulatory
system of snakes with hearts located in relatively close proximity to their heads
Answer: A
It can be inferred from the passage that which of the following is a true
statement about sea snakes?
(A) They frequently rely on waves of muscle contractions from the lower torso to
the head to supplement the work of the heart.
(B) They can not effectively regulate their blood pressure when placed in sea
water and tilted at an angle with the head pointed downward.
(C) They are more likely to have a heart located in close proximity to their heads
than are arboreal snakes.
(D) They become acutely vulnerable to the effects of gravitational pressure on
their circulatory system when they are placed in a terrestrial environment.
(E) Their cardiovascular system is not as complicated as that of arboreal snakes.
Answer: D
The author suggests that which of the following is a disadvantage that results
from the location of a snake's heart in close proximity to its head?
(A) A decrease in the efficiency with which the snake regulates the flow of blood
to the brain
(B) A decrease in the number of orientations in space that a snake can assume
without loss of blood flow to the brain
(C) A decrease in blood pressure at the snake's mid point when it is tilted at
various angles with its head up
(D) An increase in the tendency of blood to pool at the snake's head when the
snake is tilted at various angles with its head down
(E) An increase in the amount of effort required to distribute blood to and from
the snake's tail
Answer: E
The primary purpose of the third paragraph is to
(A) introduce a topic that is not discussed earlier in the passage
(B) describe a more efficient method of achieving an effect discussed in the
previous paragraph
(C) draw a conclusion based on information elaborated in the previous paragraph
(D) discuss two specific examples of phenomena mentioned at the end of the
previous paragraph
(E) introduce evidence that undermines a view reported earlier in the passage
Answer: D
In the passage,the author is primarily concerned with doing which of the
following?
(A) Explaining adaptations that enable the terrestrial snake to cope with the
effects of gravitational pressure on its circulatory system
(B) Comparing the circulatory system of the sea snake with that of the terrestrial
snake
(C) Explaining why the circulatory system of the terrestrial snake is different from
that of the sea snake
(D) Pointing out features of the terrestrial snake's cardiovascular system that
make it superior to that of the sea snake
(E) Explaining how the sea snake is able to neutralize the effects of gravitational
pressure on its circulatory system
Answer: A |
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发表于 2015-10-28 12:36:15
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