Question 135·200 Super-Hard SAT Reading Questions·Information and Ideas
Marine ecologist Amina Solberg studied the byssal threads, or protein fibers used for anchoring, of blue mussels exposed to two water-flow patterns. Both patterns had the same average current speed, but one was continuous while the other included brief, unpredictable surges. After ten days, mussels exposed to surges had produced fewer threads, yet the surge-exposed specimens required 24 percent more force to detach than mussels exposed to continuous flow. When the thickest one-fifth of each mussel's threads were clipped immediately before another test, however, the surge-exposed mussels required less force to detach than the continuous-flow mussels did.
Based on the text, which choice, if true, best accounts for the observation presented in the underlined sentence?
For an evidence-based explanation question, isolate every part of the observation that the correct choice must address. Here, a successful explanation must account for the initial advantage of one group, the selective removal of certain threads, and the subsequent reversal. Reject choices that explain only a general decrease or only one stage of the experiment.
Hints
Track the comparison
Consider how the relative performance of the two groups changes before and after the thickest threads are clipped.
Look for a complete explanation
The best choice must explain not only why clipping weakens the mussels but also why it affects one group's ranking more dramatically.
Step-by-step Explanation
Identify the pattern requiring explanation
Before clipping, the surge-exposed mussels resisted detachment better despite having fewer threads. After the thickest one-fifth of the threads were clipped, those mussels resisted detachment less effectively than the continuous-flow mussels.
Determine what the evidence must explain
A complete explanation must account for both the surge group's initial advantage and its larger loss of anchoring strength when the thickest threads were removed.
Select the explanation that fits both results
If the surge-exposed mussels concentrated their byssal material in a few exceptionally strong threads, those threads could provide the initial advantage. Clipping them would remove a disproportionate share of the group's anchoring strength, while the continuous-flow group's more evenly distributed strength would be less affected. Therefore, the correct answer is Surges prompt mussels to concentrate byssal material in a few exceptionally strong threads, while continuous currents prompt a more even distribution among threads.