LSAT 159 | Section 3 | Logical Reasoning: Q19

LR Question 19 Explanation

QUESTION TEXT: When plants are growing quickly, they take more carbon dioxide …

QUESTION TYPE: Most Strongly Supported

FACTS:

1. Fast growth makes plants a net carbon sink.
2. Slow growth makes plants a net carbon source.
3. Increase in CO2 leads to higher tropical temperatures.
4. Higher tropical temperatures slow average plant growth in the tropics.

ANALYSIS: There’s a chain of causal statements here, so the key is linking them correctly. The structure looks like this:

1. Increased atmospheric CO2 -> increased tropical temperatures
2. Increased tropical temperatures -> decreased plant growth
3. Decreased plant growth rate -> more CO2 released by plants (relative to what they absorb)

We’re asked for a supported inference based on this. It’s hard to prephrase MSS questions like this. Just be aware of any answers that exaggerate or reverse any part of the chain.

___________

1. Too strong. It never describes anything that’s inevitable.
2. This goes slightly beyond what’s stated. The stimulus only says they grow more slowly on average, but not that all tropical plants will automatically cross over into net release.
3. CORRECT. If tropical plants release enough CO2 to raise atmospheric levels substantially, that increase raises temperatures, which slows their growth.
4. The causal order is reversed here. It’s the temperature that causes the slow growth, not the opposite.
5. We don’t know that increased CO2 is the only cause for tropical temperature. Increased CO2 is just a sufficient condition, not a necessary one.