Question 114·Hard·Inferences
Marine biologists compared two populations of the same coral species. One population lives on open-water reefs where temperatures vary little, while the other inhabits shallow tide pools that can warm by up to during the day. In laboratory tests, tide-pool corals survived exposure to temperatures that killed most open-water corals, even though genetic analysis showed the two populations are nearly identical. These results most strongly suggest that ______
Which choice most logically completes the text?
For inference questions like this, restate the key result and the key constraint (here: different heat tolerance despite near-identical genetics). Then choose the conclusion that best explains the result using only factors the passage actually provides (here: the more variable, warmer tide-pool environment) and avoid options that add new mechanisms or time scales not supported by the text.
Hints
Locate the key contrast
Look at how the environments of the two coral populations differ, and how their survival in the lab test differs.
Use the genetic information
The passage says the two populations are nearly genetically identical. What does that suggest about whether genes can explain the difference in heat survival?
Think about cause and effect
Ask yourself: what factor mentioned in the passage could have caused one group to tolerate higher temperatures than the other, if not genetics?
Test each choice against the data
Eliminate any choice that contradicts the experiment results (who survived, who died) or adds extra claims not supported by the passage.
Step-by-step Explanation
Restate the key facts
First, summarize what the passage tells you:
- Two populations are from the same coral species, so we expect them to be genetically similar.
- One lives on open-water reefs with little temperature variation.
- One lives in shallow tide pools that can warm by up to during the day.
- In lab tests, tide-pool corals survived higher temperatures that killed most open-water corals.
- Genetic analysis shows the two populations are nearly identical.
Identify what needs explaining
Ask yourself what needs explaining:
- One group handles heat much better than the other even though their genes are almost the same.
- So a strong inference should explain increased heat tolerance without relying on major genetic differences.
- The explanation should connect to a stated difference between the groups (their environments).
Use the environmental difference as a clue
The key environmental contrast is:
- Open-water reefs: temperatures are relatively stable.
- Tide pools: temperatures can spike by up to during the day.
If genetics can’t account for the lab-survival difference, the most supported inference is that regular exposure to temperature swings has led to acclimation/physiological adjustments that improve heat tolerance.
Match the reasoning to the choices
Evaluate each option against the passage:
- The "undetected genetic differences" idea is possible in the real world, but the passage emphasizes that the populations are nearly identical genetically, so this is less strongly suggested than an environment-driven explanation.
- The "different symbiotic partners" idea introduces a new mechanism not mentioned in the text, so it is not what the results most strongly suggest based on the given information.
- The "distinct lineage over many generations" idea goes beyond the evidence and conflicts with the strong emphasis on genetic similarity.
- The remaining choice directly matches the data: environmental temperature fluctuations align with higher heat survival despite near-identical genetics.
Therefore, the correct answer is environmental fluctuations can induce physiological changes that give corals heat tolerance without requiring genetic differences.