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OG In terrestrial environments, gravity places special

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OG In terrestrial environments, gravity places special

Post Thu Jul 27, 2017 8:01 pm
In terrestrial environments, gravity places special demands on the cardiovascular systems of animals. Gravitational pressure can cause blood to poolinthe 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 similarspatial 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.

435) 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 inthe same way.

436) 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

437) It can be inferred from the passage that which ofthe 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.

438) 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

439) 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.

440) 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

441) 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

442) 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

Q435: B
Q436: B
Q437: B
Q438: A
Q439: D
Q440: E
Q441: D
Q442: A

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Top Reply
Post Tue Nov 28, 2017 3:43 pm
Ladder:
This is a great multi-group passage. The test-writers know that skimmers are not going to be able to recall the different properties of these snakes, so by reading at 150 WPM, and laddering what each group does, you’re going to be beautifully positioned to capture some big points. Let’s move into it. What’s the overall point of this passage? To show how evidence about how snakes have adapted to optimize their circulation based on what environment they live in. That’s it. That understanding, and our diagramming is going to pay off big time when we move to the questions.

1 = Gravity -> Blood pool lower part of the body; terrestrial: guard against gravity
2 =/+ Terrestrial vs Sea: Sea: water = OK; out of water, no blood to head; proves adaptation
3 =/+ Terrestrial: heart closer to head ⇐=====X==0; Sea: ⇐===X====0; arboreal ⇐=======X=>; suggests adaptations

Check out the diagramming in the ladder. Why do we go to the trouble to diagram here? Because a question or two in, it would be way too confusing to try to remember which snake does what, and the entire passage centers on those examples, so we’re definitely going to get some questions about them.


OG 2018 Pg. 383 Q442
435 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.

Question Type: Inference
Forecast: This question is asking us to find the option that can be firmly concluded on the basis of what’s actually in the passage.

A) Does this passage allow us to conclude whether the disadvantages of an adaptation (heart placement or ANYTHING ELSE) outweigh the advantages? No way. On the basis of the passage, yes, there are some disadvantages if a snake is placed in an environment it isn’t adapted for, but that would be outrageous to then try to conclude that the disadvantages outweigh the advantages.
B) Yes! Remember in P2, sea snakes are removed from water and they struggle to balance blood flow? Why did the author refer to this example? To show how adaptations in terrestrial snakes enable them to solve that problem.
C) Too extreme. Just because the author used one way to demonstrate how an adaptation can help in no way means that that is the ONLY WAY to evaluate the effectiveness of that adaptation. Chuck it.
D) Utterly without a basis. The examples in the passage each show how one species has optimized to one type of environment. How is this option going to get away with the claim that the SAME species will adapt in similar ways to strikingly different environments? We can’t, at all. Gone.
E) This option also strays from the scope of what can be supported by the passage. How on earth could we conclude that different species wouldn’t actually adapt to the environment in the same way? We can’t, so this is also gone.

B

OG 2018 Pg. 383 Q443
436 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

Question Type: Detail
Forecast: Alright, let’s go to the part of the passage dealing with how sea snakes are adapted to water. That’s right here in P2:
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.

What option says that? B) pressure gradients in the water surrounding the sea snake counter the effects of vertical pressure gradients within its blood vessels
A) Although true, the heart placement isn’t offered as the reason why pressure remains the same when in water
C) Mentioned nowhere
D) Wrong snake! Arboreal snakes (not sea snakes) often pause momentarily to wiggle their bodies, causing waves of muscle contraction that advance from the lower torso to the head.
E) Read this option and think about what it actually means. It’s horrific. If the inward force from water exceeds the outward force from their bodies, wouldn’t that mean that sea snakes would be crushed? The passage said that the pressures are balanced.

B

OG 2018 Pg. 383 Q444
437 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.

Question Type: Inference
Forecast: Let’s zero on in the part discussing snakes that often need to assume a vertical posture: 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.

A) 180. It’s sea snakes that are vulnerable to vertical posture (if out of water).
B) Here we go: Let’s also refer back to our diagram. Where are sea snakes hearts? Midpoint. Where are arboreal snake hearts? Near the head. This option says: arboreal snake hearts are less likely to be located at the midpoint of their bodies than is the case with sea snakes. Yep, that can be definitively concluded.
C) There might be more pooling at arboreal snake tails, but then the passage explains this additional 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.”
We can’t conclude that arboreal snakes are therefore any less capable of managing lower body pooling than sea snakes. Gone.
D) Not mentioned or suggested anywhere. Summarily dump.
E) Flat out 180. The passage literally explains that arboreal snakes are able to use contractions to move blood from the lower torso to the head. This is clearly a punishment option for people who skim it and miss the word “unable”

B

OG 2018 Pg. 384 Q445
438 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

Question Type: Purpose
Forecast: What is the benefit of the sea snake ocean removal example? To use sea snakes as proof that terrestrial snakes have adapted in a way to optimize them to their environment.

A) Bam! The sea snake example was provided to highlight how terrestrial snakes have adapted to overcome a challenge.
B) Huh? Arboreal snakes aren’t actually relevant to why the sea snake example was mentioned in P2. The arboreal snake example was later used as yet another type of adaptation. This option is Out of Focus of the question as it relates to the point of referencing sea snakes in P2.
C) Similar to B. C somehow presents the case that the sea snake example in P2 that is used to highlight an adaptation by terrestrial snakes is related to the arboreal snake example in P3. Out of Focus as well.
D) We’re never actually told that one snake has a superior circulatory system, but rather how each is adapted to suit its own environment.
E) Babble punishment for skimmers. Remember that terrestrial snakes have hearts closer to their heads than sea snakes? This option gets it all backwards. The sea snake example is used to show how terrestrial snakes have adapted to overcome a challenge, not to explain how they are adversely affected. This option is designed to punish people who get lost about which snake it’s talking about, specifically, this option is designed to punish those who think the sea snake example was used to show how sea snakes are ill adapted, but that wasn’t the point at all.

A

OG 2018 Pg. 384 Q446
439 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 seawater 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.

Question Type: Inference
Forecast: Taking the info the passage provides about sea snakes, let’s see which option MUST BE TRUE

A) Nope! Wrong snake. It’s arboreal snakes that rely on such contractions. Check out P3.
B) Totally off. Sea snakes are in trouble when taken OUT of the water, but are perfectly suited when in water. This option is a 180.
C) Another 180. A Sea snake is less likely to have a heart near it’s head. Sea snake hearts are near their midpoints.
D) Now here we go! When sea snakes are removed from the water, they really struggle to manage blood flow. This option is supported 100%.
E) Totally Out of Focus. There is no mention of complication or simplicity anywhere in the passage. Chuck it.

D

OG 2018 Pg. 384 Q447
440 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

Question Type: Inference
Forecast: So now, in the passage, which snake has a heart near its head? Terrestrial, and especially arboreal. What disadvantage is mentioned? The distribution of blood at the lower part of its body.

A) Since the heart is near the brain, this option is a 180. Circulation to the brain is just fine.
B) Just like A, this option delivers a 180 because it’s somehow suggesting that blood flow to the brain is a problem. Nope.
C) Midpoint was mentioned in regard to sea snakes, and certainly not as a challenge for terrestrial and arboreal snakes. Warp/Out of Focus.
D) This option is the runner up, but concluding the opposite of what’s provided isn’t actually supported. It might be reasonable to imagine that if a snake with a heart near its head were hanging down that blood would pool at its head, but we can’t actually reach that conclusion from what’s in the passage with the sufficiency we’d need in an Inference question. Gone.
E) Yes! We know that the placement of the heart near its head enables better blood flow to the head when climbing, but that in turn requires more effort for the blood to travel to and from its tail. That disadvantage is then remedied by body contractions then help redistribute blood flow.

E

OG 2018 Pg. 384 Q448
441 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

Question Type: Paragraph Purpose
Forecast: This question is asking us what the author’s purpose was with the 3rd paragraph. Let’s just hop back to our ladder and then hit the options:
3 =/+ Terrestrial: heart closer to head ⇐=====X==0; Sea: ⇐===X====0; arboreal ⇐=======X=>; suggests adaptations. It’s the ‘suggest adaptations’ component that really defines the agenda.

A) Paragraph 3 is absolutely within the same topic as the rest of the passage, so get rid of this significantly warped hunk of junk.
B) There is no more or less effective method of achieving the objective of adapting to the environment. The point is that the adaptation takes place to optimize that species to its environment. Warp.
C) This is the narrowest Warp. Yes, the author is offering the suggestion that adaptation takes place to optimize that species to its environment, but it’s inaccurate to say that the conclusion was specifically drawn (solely) based on the information elaborated in the previous paragraph. More evidence was put forth in the third paragraph itself.
D) Yes, this paragraph provides further exemplification of the kind of adaptations pointed out in the prior paragraph. “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.”
E) 180. Everything in this passage works toward the same general theme--no contradiction is taking place.

D

OG 2018 Pg. 385 Q449
442 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

Question Type: Passage Purpose
Forecast: This question is central to the point of the whole passage, and in fact, we even touched on this exact item in our passage analysis: “What’s the overall point of this passage? To show how evidence about how snakes have adapted to optimize their circulation based on what environment they live in. That’s it.” So let’s find our option.

A) Bingo! The singular objective of the passage is to demonstrate (and point to) how snakes have adapted in such a way as to optimize blood flow based on their environment.
B) Nope. Too narrow in focus. Although this does happen, is the comparison between sea snakes and terrestrial snakes the ONLY thing the author seeks to do? No.There is another example beyond these two, and again the primary objective is to show how evidence about how snakes have adapted to optimize their circulation based on what environment they live in.
C) Nope. Too narrow in focus. Just like B, yes the author does explain why the circulatory system of the terrestrial snake is different from that of the sea snake, BUT is that the SOLE objective. No. Gone.
D) We’ve seen this as a running theme in incorrect options in this passage: the notion of superiority. The author doesn’t claim that any one adaptation is superior, but rather that each species as optimized to its particular environment.
E) Nope. Too narrow in focus again. Although this does happen, is the discussion about how sea snakes have adapted to suit their environment the SOLE thing the author seeks to do? No. The primary objective is to show how evidence about how snakes have adapted to optimize their circulation based on what environment they live in.

A)

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