Question 8·200 Super-Hard SAT Reading Questions·Information and Ideas
Marsh Flea Beetles' First Choices in Paired Feeding Trials
| Trial | Source plant's salinity | Litorin level on leaf disk | Leaf disk choice rate |
|---|---|---|---|
| 1: unmodified disks | 10 parts per thousand | Naturally low | 24% |
| 1: unmodified disks | 30 parts per thousand | Naturally high | 76% |
| 2: modified disks | 10 parts per thousand | Raised to high | 69% |
| 2: modified disks | 30 parts per thousand | Lowered to low | 31% |
Sea lavender grown under high-salinity conditions produces more litorin, a waxy surface compound, than sea lavender grown under low-salinity conditions. Researchers investigated whether marsh flea beetles respond to litorin or to another leaf property associated with salinity. In Trial 1, the researchers offered each beetle one leaf disk from each salinity condition. Before Trial 2, they selectively reversed the disks' litorin levels while leaving their sodium concentrations, toughness, and color unchanged. The table shows the percentage of beetles that first fed on each type of disk.
Which choice best describes a conclusion supported by the experiment?
When an experiment begins with two factors that vary together, identify the trial that separates or reverses them. Then compare each option's strength with what the evidence establishes: prefer a cautious description of the observed pattern over claims about an exclusive cause, an unisolated independent effect, or the only possible causal pathway.
Hints
Identify the key trial
Focus on Trial 2, in which the researchers separated two factors that occurred together in Trial 1.
Track what changed
Compare the source plant's salinity with the experimentally adjusted feature of the disk that received 69% of first choices.
Check the scope of each conclusion
Distinguish a conclusion describing which factor the choices followed more closely from claims that identify an exclusive cause or infer an independent effect.
Step-by-step Explanation
Interpret the unmodified trial
In Trial 1, 76% of beetles chose the high-salinity disk, which also had naturally high litorin. Because salinity and litorin varied together, this trial alone cannot identify which factor better accounts for the preference.
Analyze the reversed levels
In Trial 2, the low-salinity disk had its litorin raised and received 69% of first choices. The high-salinity disk had its litorin lowered and received only 31%, even though the treatment did not change sodium concentration, toughness, or color.
Distinguish support from overclaiming
The preference followed the experimentally changed litorin levels more closely than the source plants' salinity conditions. This supports a comparative conclusion about the observed pattern, but it does not prove that litorin was the only relevant property or that salinity could affect choice only through litorin.