Question 148·Easy·Central Ideas and Details
Marine biologists studying a reef in the Pacific recently discovered that some coral species release chemical signals when water temperatures climb to a critical threshold. Nearby corals detect these signals and respond by expelling their symbiotic algae sooner than they otherwise would, which may help them avoid fatal overheating. The researchers believe this early warning system can protect corals during brief heat spikes, although it is unlikely to prevent bleaching during long-lasting periods of high temperature.
Which choice best states the main idea of the text?
For main idea questions, first briefly paraphrase the entire passage in your own words—who or what is it about, and what is the main point about that subject? Then test each answer choice against this paraphrase, eliminating options that (1) contradict any specific detail, (2) contain extreme or absolute words not supported by the text, or (3) focus on a minor detail rather than the overall discovery or argument. Choose the answer that best matches your paraphrased summary without adding or twisting information.
Hints
Focus on the overall discovery
Look back at what the marine biologists "recently discovered." What new behavior or system did they find among the corals?
Connect the beginning and the end
Compare the first sentence (what happens when temperatures reach a threshold) with the last sentence (what the researchers believe this system can and cannot do). What idea ties these together?
Watch out for contradictions and extremes
Check each answer for words like "only," "invariably," or "uncertain." Ask yourself: does the passage actually say that, or does the answer go beyond or against what is stated?
Think: summary, not detail
Choose the option that captures what the whole passage is about, not just one effect, one condition, or one part of the research.
Step-by-step Explanation
Identify the question type
The question asks, "Which choice best states the main idea of the text?" That means you need a choice that sums up what the entire passage is mostly about, not a small detail or an exaggerated claim.
Restate the passage in your own words
Paraphrase the paragraph:
- Scientists found that some corals release chemical signals when the water gets too hot.
- Nearby corals sense these signals and respond by getting rid of their algae earlier than they otherwise would.
- This early response may help them avoid being killed by short bursts of heat, but it probably does not save them in long periods of high temperature.
So overall, the passage is about a newly discovered early warning system among corals that involves chemical signals and helps with brief heat spikes.
Test each answer against the passage
Now compare each choice to your summary:
- Ask: Does this choice match the main point of the whole paragraph?
- Check for words that contradict the text (like "only," "invariably," or "uncertain") or for claims the scientists did not make.
Quick checks:
- If an answer directly contradicts a stated detail (for example, timing of algae release), it cannot be correct.
- If an answer adds extreme language that the passage does not support, it is also wrong.
- If an answer ignores the discovery about chemical signaling and focuses on something else, it likely misses the main idea.
Match the best summary to the passage
The correct choice must mention the key discovery—how corals interact—and reflect that this interaction helps during dangerous heat. Only B) Corals communicate through chemical signals that warn neighboring corals of dangerous heat. accurately summarizes what the researchers found and how it functions, making it the best statement of the main idea.