Question 33·Hard·Central Ideas and Details
For much of the twentieth century, ecologists maintained that seagrass meadows were low-productivity habitats that contributed little to global carbon cycling. Beginning in the 1990s, however, researchers showed that, per square meter, seagrasses can sequester carbon at rates rivaling or exceeding those of tropical rainforests because organic material becomes buried in the sediments beneath the grass beds. This insight has led coastal management agencies to reassess the ecological importance of seagrass meadows and to launch programs aimed at protecting and restoring them.
Which choice best expresses the main idea of the text?
For main-idea questions, briefly paraphrase the passage’s full arc (especially any contrast or change over time) in one sentence. Then pick the option that matches that paraphrase without narrowing to a single detail (like one comparison) or giving only the conclusion (like one action taken). Eliminate choices that are true-but-incomplete or that add implications the passage doesn’t make.
Hints
Hint 1: Look at the beginning and the end
Pay special attention to the first and last sentences. What did people used to think, and what are they doing now as a result of new information?
Hint 2: Capture the whole passage, not just one detail
The correct answer must account for the change over time and the resulting actions, not just a single fact like the rainforest comparison or the sediment detail.
Hint 3: Watch for choices that are only partially true
Some answers will repeat a true detail from the passage but leave out another essential part (like the older misconception or the agency response). The main idea should include the passage’s full arc.
Step-by-step Explanation
Identify the overall structure of the passage
Read the passage and notice how it is organized over time:
- First sentence: describes the old view (for much of the twentieth century, ecologists thought seagrass meadows were low-productivity and contributed little to carbon cycling).
- Second sentence: presents new research findings (since the 1990s, scientists have shown seagrasses can sequester a lot of carbon because organic material becomes buried in sediments).
- Third sentence: shows the consequence of that new research (coastal management agencies are reassessing seagrass importance and launching protection and restoration programs).
So the passage moves from past misconception → new evidence → new conservation actions.
Summarize the main idea in your own words
State the main point in one sentence before looking at the choices:
- People used to think seagrass meadows didn’t matter much for carbon cycling.
- Research starting in the 1990s showed they can store carbon at very high rates (with carbon buried in sediments).
- That discovery led agencies to reevaluate seagrasses and begin protecting/restoring them.
The best answer should capture the shift in thinking and the resulting action.
Eliminate choices that are too narrow
Check each option against your summary:
- Some choices focus mainly on one part of the passage (just the burial mechanism, just the rainforest comparison, or just the agency programs) and leave out the other key parts.
- A main-idea answer should not read like a single detail or only the conclusion; it should reflect the passage’s full arc: earlier belief → new findings → response.
Select the choice that captures the full arc
The correct choice is the one that includes both (1) the overturning of the old view that seagrasses were unimportant to carbon cycling and (2) the fact that this has spurred conservation initiatives. That is:
Recent findings that seagrass meadows store large amounts of carbon have challenged a longstanding view of them as unimportant to carbon cycles and spurred conservation initiatives.