Reading Comprehension

OG-15 Passage-6 Terrestrial environment


question 20) 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.


doubt: arboreal and terrestrial snake are same?
doubt: Didn't get official explanation

This question requires using information given
about how arboreal snakes, which are frequently
in vertical postures, have adapted to gravity's
influence to make an assumption that other
terrestrial snakes that are frequently in these
postures are likely to have similar adaptations.
The passage implies that sea snakes have hearts at
the midpoint of their bodies because the water's
pressure gradients help distribute blood evenly. It
then illustrates that arboreal snakes have hearts
closer to their heads to help keep blood flowing to
their brain when they are in vertical postures.




I referred to passage where it talks about this:

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.


It talks about arboreal snake has this problem, which is solved by adaptation and when climbing arboreal snakes contract that improves the flow.



question 21)
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


doubt: how A and why not D?

What I understood is terrestrial snakes have a edge over sea snake.

then how come it reaches to the point of "terrestrial snakes without adaptations"

Hey Vishal,

I think your confusion stems from the fact that passage compares "sea snakes" to "terrestrial snakes" and the word "arboreal" means "referring to trees" so they are the exact same thing as "terrestrial snakes."

It's pretty mean of the GMAT to assume we know the definition of the word "arboreal," but then again, the GMAT isn't the nicest exam in the world. Just think of all those Quant definitions we have to know!

Question 20: What's true of vertical T-snakes?

Prediction: Heart-to-head small distance; blood flow improved when they "assume a vertical posture."

The correct answer is (B). This matches our prediction of "heart-to-head" small distance. It's OKAY to make the inference from "arboreal" to "terrestrial" because there is no other information in the passage we can use to make our prediction. We have to assume that somehow arboreal = terrestrial, otherwise this would not be a fair question! Also, this is an Inference question, not a Detail question, so the correct answer does not have to be verbatim from the passage, it simply has to be strongly SUPPORTED by the passage.

Question 21:

This is a Function question. The phrase "in order to" means WHY does the author take this action? This type of question is incredibly difficult to answer if you haven't already found the function of the paragraph that this detail is in.

Question rephrase: WHY mention the C-system of snakes removed from ocean?

To find our prediction, let's read a couple sentences around the detail:

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.

Prediction: to show how T's adaptation are more effective

(D) is a perfect match. It nicely restates the sentiment expressed in the passage.

(A) is incorrect. If the point of this detail was to "illustrate what would occur w/o the adaptations in vertical orientations," then I would expect the next sentence to discuss the vertical orientations, or say something like, "It's a good thing terrestrial snakes are not like this, because otherwise..." but no such "consequences" are mentioned.

Notice the pattern of the sentences from the passage:

-state a fact (sea snakes act this way our of the water)
-explain WHY it is in the passage (it shows T-snakes have a cool adaptation)

In addition the "vertical" movement was mentioned 2 sentences earlier, and there is nothing to indicate we need to bring that detail down and relate it to these sentences. It feels like we've shifted to a new topic: from the vertical movement, to the behavior of sea snakes out of water. Remember, it's a Function question, not an Inference question, so we can be more direct and literal. You don't necessarily have to piece together multiple Details to make something new. Functions questions are more straightforward.

I hope this helps!