In terrestrial environments, gravity places special demands on the cardiovascular systems of animals. Gravitational pressure can cause blood to pool...
GMAT Reading Comprehension : (RC) Questions
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?
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| In terrestrial environments, gravity places special demands on the cardiovascular systems of animals. | What it says: On land, gravity creates challenges for animal hearts and blood circulation. What it does: Introduces the main topic and sets up the central problem Source/Type: General scientific fact Connection to Previous Sentences: Opening statement - establishes the foundational concept Visualization: Imagine a dog standing upright - gravity pulls blood down toward its feet, making it harder for the heart to pump blood up to the brain Reading Strategy Insight: This is a classic RC opener - broad topic introduction. Expect the passage to narrow down to specific examples. What We Know So Far: Gravity creates cardiovascular challenges for land animals What We Don't Know Yet: What specific challenges? Which animals? What solutions exist? |
| 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. | What it says: This explains exactly what "special demands" means - blood gets stuck in lower body parts, can't reach the brain What it does: Clarifies and elaborates on the previous sentence Source/Type: Scientific explanation/fact Connection to Previous Sentences: This ELABORATES on sentence 1. The first sentence said gravity creates "special demands" - now we learn exactly what those demands are. Feel relieved here - this is clarification, not new complexity Visualization: Think of blood like water in a tall building - without a strong pump, the water stays on the first floor and can't reach the 10th floor (the brain) Reading Strategy Insight: Classic pattern - general statement followed by specific explanation. The passage is becoming clearer, not more complex. |
- The passage doesn't discuss disadvantages outweighing advantages
- The heart placement adaptation does create a trade-off (longer distance to tail), but this is solved by another adaptation (wiggling)
- The passage presents adaptations as successful solutions, not as problematic trade-offs
- Doesn't the passage mention that heart placement creates a problem for tail circulation?
→ Yes, but this problem is solved by the wiggling adaptation - the passage shows adaptations working together, not disadvantages outweighing advantages
- The passage explicitly uses sea snakes' failure out of water to illustrate terrestrial snakes' challenges
- Sea snakes are "not well adapted" to terrestrial environments, and their reaction (circulation failure) demonstrates the problems terrestrial snakes have solved
- This matches the passage structure: problem illustrated by failure → solutions by adapted organisms
- The passage doesn't claim this is the "only" way to evaluate adaptations
- The passage uses one comparison method but doesn't state it's the exclusive method
- "Only" makes this too absolute and extreme
- Doesn't the passage evaluate terrestrial snake adaptations by comparing to sea snakes?
→ Yes, but saying this is the "only" way goes beyond what the passage claims
- The passage compares different species (sea snakes vs. terrestrial snakes), not the same species in different environments
- Sea snakes and terrestrial snakes are different species, not the same species in different habitats
- The adaptations described are quite different (heart placement, wiggling), not "remarkably similar"
- Aren't all the snakes in the passage the same species facing gravity?
→ No, sea snakes and terrestrial snakes are different species that evolved in different environments
- The passage doesn't compare multiple species living in the same environment
- The comparison is between species from different environments (sea vs. land)
- The passage doesn't provide information about whether different species in the same environment adapt similarly or differently
- Don't arboreal snakes and other terrestrial snakes live in the same environment but adapt differently?
→ Arboreal snakes live in trees (specialized terrestrial environment) and show more extreme versions of the same adaptations, not completely different approaches