Question 95·200 Super-Hard SAT Reading Questions·Information and Ideas
Annual plants in regions with erratic rainfall may reduce risk either by delaying germination or by completing reproduction quickly after germinating. Researchers collected seeds from six populations of an annual plant located along a gradient of rainfall variability. To reduce the effects of conditions experienced by the original parent plants, the researchers grew one generation under identical greenhouse conditions and then tested that generation’s descendants. The descendants received either one large watering pulse or three smaller pulses containing the same total amount of water. Neither the proportion of seeds germinating nor the time to germination varied systematically with rainfall variability at the source sites. However, descendants from more variable sites reached flowering sooner after germination, although average adult mass was similar across populations. The greenhouse did not reproduce natural temperature fluctuations or competition. Taken together, the findings suggest that ______
Which choice most logically completes the text?
For inference questions about experiments, identify what the design controls, separate positive findings from null findings, and distinguish association from causation. Choose the conclusion that remains limited to the measured traits and tested conditions rather than extrapolating to untested environments or proposing an unmeasured mechanism.
Hints
Consider the common conditions
Ask what growing one generation in the same greenhouse is intended to reduce. Remember that this procedure does not make the populations genetically identical.
Distinguish the life stages
Compare what the researchers observed about germination with what they observed after germination.
Watch the scope and causality
Determine which conclusion stays within the tested conditions and avoids attributing the observed association to a specific cause that the researchers did not isolate.
Step-by-step Explanation
Interpret the study design
Growing an intervening generation under identical greenhouse conditions reduces the likelihood that differences among the tested descendants simply carried over from the original parent plants’ environments. However, the design does not make the populations genetically identical.
Separate the findings by life stage
Germination proportion and germination time did not vary systematically with source-site rainfall variability under either watering pattern. In contrast, descendants from more variable sites flowered sooner after germination.
Respect the study’s limits
The association does not prove that rainfall variability, rather than another correlated source-site factor, caused the flowering-time differences. Likewise, the germination results cannot be generalized to every natural condition because the experiment tested only two watering patterns and omitted natural temperature fluctuations and competition. Similar adult mass also does not establish an unmeasured increase in growth rate.
Select the supported conclusion
Therefore, the best completion is “the results are consistent with inherited population differences in post-germination timing, while providing no evidence of inherited differences in germination under the watering patterns tested.”