In terrestrial environments, gravity places special demands

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.



In above question, I don't understand why sea snake become vulnerable to the effects of gravitational pressure.

It is already mentioned in the passage, if sea snake are placed in terrestrial environment

"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".

kindly help.

Question 5

The piece of the passage you quoted discusses both terrestrial (or land-based) snakes and sea snakes. The passage draws a contrast between these two types of snake, so it's important to be very clear about what information applies to each kind of snake. Question #5 asks about sea snakes, so here's a look at what the passage says about them in particular:

In the second paragraph of the passage, the author talks about an experiment on sea snakes in order to illustrate a problem facing terrestrial snakes (which seems incredibly unfair to the sea snakes, but I guess that is beside the point).

While they are in the water, sea snakes maintain the same distribution of blood throughout their bodies no matter how they are oriented in space. This is because water acts as a supportive medium that counteracts the effects of gravity. But what happens when you take the snakes out of their supportive, watery environment?

That's exactly what the experimenters did -- they took the sea snakes out of the water and "tilted [them] at various angles with the head up." In doing so they found that, when the sea snakes didn't have water to counteract the effects of gravity, the blood pressure in their brains fell to zero (seriously, what a terrible day to be a sea snake).

Terrestrial snakes, on the other hand, "do not experience this kind of circulatory failure" when subjected to the same treatment, because terrestrial snakes have adapted to regulate their blood pressure in those orientations.

From this, we can infer that sea snakes "become acutely vulnerable to the effects of gravitational pressure on their circulatory system when they are placed in a terrestrial environment." (D) is the correct answer to question #5.

One more note: the piece of the passage that you quoted describes one of the ways in which terrestrial snakes have adapted to better regulate their blood pressure in a terrestrial environment. Because their hearts are closer to their heads, they are better able to ensure blood circulation to their brains. Sea snakes, on the other hand, have not adapted in this way.

I hope that helps!

Hi GMATNinja! Please could you explain why the OA for Question 6 is E and not A?

Question 6

Question 6 asks us to identify a disadvantage that results from the snake’s heart being in close proximity to its head. The final paragraph of the passage discusses this possibility. Take a look:

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.... 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.

Now here’s (A):

(A) suggests that when a snake’s heart is close to its head the snake’s ability to get blood to the brain is impaired. But the passage indicates the opposite. It states that the heart being close to the brain “helps to ensure circulation to the brain.” Eliminate (A).

And here’s (E):

In the second boldface portion of the passage above, the author makes clear that when a snake’s head is close to its heart the blood is forced to flow further to its tail. This would presumably require a greater amount of effort as (E) indicates. For that reason, (E) is the best choice for question 6.

I hope that helps!

Hi,
I was also confused between A and C, but chose A because it gives a broader view of the passage. Explaining the circulatory system of terrestrial snake and the sea snake was an example to discuss the main idea of the passage i.e. the effects of gravitational pressure on the circulatory system.
Hope this helps!

Is 10 min total time for this passage too much or about right? Considering all answers are correct.

10 minutes for 8 correct are more than fine.

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.

Hope it helps

Hi. Why is (A) wrong for question3? It is mentioned that gravity makes it harder for terrestrial snakes and the lack of neutralizing forces, as is the case in water, makes it harder for terrestrial snakes to maintain vertical positions.

It is true that the snakes are adapted to it, but they have adapted to it because it would have been harder without the adaption.

Option (B) says about the adaptation. It is true that the result of adaptation removes that disadvantage but the question does not explicitly mention IF the adaptation effect needs to be considered.

­The passage specifically tells us that many terrestrial snakes in similar (head-up) spatial orientations do NOT experience this kind of circulatory failure. Why not? Because they have certain adaptations including the waves of muscle contractions and the fact that the heart is close to the head.

That passage describes how these adaptations SOLVE the circulatory problems caused by gravity, so there's no reason to think that those snakes are more likely to be susceptible to circulatory failure in vertical postures than are sea snakes.

As for (B), the passage tells us that the terrestrial snakes do in fact have these adaptations, so we must consider those adaptations when answering the question.

I hope that helps!­