Question 110·Medium·Command of Evidence
After a severe wildfire, ecologists studying a pine forest noticed a surge in soil microbes that specialize in breaking down charred wood. The team proposes that this microbial bloom is a key reason pine seedlings in burned soil often grow faster than seedlings in unburned soil.
Which finding, if true, would most directly support the ecologists’ proposal?
For “support the claim” Reading & Writing questions, first restate the claim in your own words, focusing on what is being proposed as the cause or explanation. Then scan the choices and eliminate any that (1) introduce a different cause, (2) merely describe a pattern or correlation without testing the cause, or (3) give background information not tied to the claim. Look for evidence that directly tests the proposed cause—ideally by comparing situations where the key factor is present vs. absent while other conditions remain similar.
Hints
Clarify the proposal
Focus on the exact claim: the ecologists are not just saying that seedlings grow faster in burned areas; they are saying that a surge in specific soil microbes is a key reason why this happens.
Think about cause vs. alternative explanations
Ask yourself: which choice helps show that the microbes themselves are responsible, instead of something else like light or temperature that might also change after a wildfire?
Look for an experimental comparison
Check if any answer describes a setup where conditions are kept the same except for the presence or absence of those microbes, and then measures how the seedlings grow under each condition.
Step-by-step Explanation
Restate what the scientists are claiming
The ecologists propose a cause-and-effect relationship: the surge in soil microbes causes pine seedlings in burned soil to grow faster than seedlings in unburned soil. That means we’re looking for evidence that when these microbes are present, seedlings grow faster, and when they’re absent, seedlings do not get that growth boost.
Decide what kind of evidence would be strongest
To strongly support a causal claim, you want an experiment that isolates the factor in question (the microbes) while keeping other conditions the same. In other words, the best answer will:
- Compare situations with and without these microbes
- Keep other things (like light, temperature, soil source) as similar as possible
- Show that seedling growth changes when the microbes are removed or added
Test each choice against that standard
Go through the options:
- Choices about sunlight or soil warmth point to alternative causes for faster growth, not evidence that microbes are the key reason.
- A choice describing a long-term microbe trend without tying it to seedling growth does not test whether microbes cause faster growth.
- Only one choice describes using the same burned soil but removing microbes (sterilizing) and then observing that seedlings grow more slowly, which directly supports the proposal.
State the correct answer
The finding that seedlings grown in burned soil that was sterilized grew much more slowly than seedlings grown in the same burned soil left unsterilized most directly supports the ecologists’ proposal, because it shows that removing the microbes removes the growth advantage.