An explanation question about a study tests whether you can explain a result after researchers change something. Read the result the question points to, then compare it with what happened before the change. Name the groups and track what changed between tests. Ask what the change tells you about why the groups differed, and predict a cause that fits both results. An explanation must explain the difference between groups, not only describe something that could affect both.
Hints
- Hint 1
Read the underlined sentence for what changed before the second test. What did the researchers remove?
- Hint 2
Which group needed more force before clipping, and which needed more afterward? Track the change in the groups’ order.
- Hint 3
Ask why removing those threads changed the groups’ order. What might the change tell you about the role of those threads in each group?
Step-by-step
Use clipping to explain the reversal
Step 1Identify what the test removes
The underlined test removes the thickest one-fifth of each mussel's threads. We're explaining why surge-exposed mussels then need less force to detach than continuous-flow mussels. Both groups lost the same share of threads, chosen by thickness, so the cut tests the role of thick threads.
- Step 2
Compare strength before clipping
Which group held on more strongly before clipping? Surge-exposed mussels had produced fewer threads but required 24 percent more force to detach. More force means stronger anchoring, so fewer threads didn't mean weaker anchoring. We need to explain that earlier advantage as well as the result after clipping.
- Step 3
Work out what the reversal shows
After clipping, the surge-exposed mussels required less force to detach. Why did their advantage turn into a disadvantage? Cutting the thickest threads hurt the surge group more, which suggests it depended more on those threads for strength. Removing 20 percent of the threads doesn't have to remove 20 percent of the strength, because some threads can do much more of the holding. Let's look for a cause that gives the clipped threads a larger role in the surge group.
- Step 4
Match the cause to both results
Concentrating byssal material in a few exceptionally strong threads explains how fewer threads can hold more firmly. Clipping those thick threads removes much of that strength, while a more even distribution among threads leaves continuous-flow mussels with more strength in the threads that remain. Choice A.