A finding question about an experiment tests whether a result supports a proposed cause and effect. Put the hypothesis into a few words, then trace each link from cause to effect. Ask what the researchers change and what they measure, because those tell you which groups to compare. Predict how the measured result should differ if the hypothesis holds. A finding can show one part of a chain without showing that the cause leads to the effect.
Hints
- Hint 1
Start with Lian’s opening hypothesis and separate what happens to the sender from what should happen to the receiver.
- Hint 2
Look at what the sealed barriers change. Which part of the proposed chain do they test?
- Hint 3
Translate the leaf measurement into a test of defense. How should the amount eaten change if a receiver’s defense becomes more effective?
Step-by-step
Follow the signal from sender to receiver
Step 1Trace the proposed chain
Lian links volatile chemicals released by damaged sagebrush plants to nearby plants that boost their anti-herbivore defenses, so a supporting result needs to connect both ends. What has to happen for that chain to work? Chemicals from a damaged sender must reach an undamaged receiver through the air and help it resist feeding. The key effect is a change in the receiver’s defense, rather than damage to the sender alone.
- Step 2
Read the test of defense
How can we test whether that help travels through the air? The sealed barriers that prevented air exchange block the proposed route, while the open arrays leave it available. All receivers then face identical numbers of caterpillars, so the amount of leaf tissue eaten gives us a common test of defense. Less tissue eaten means the receivers resisted feeding more effectively.
- Step 3
Connect air exposure to less feeding
The finding with significantly less leaf consumption tests whether the chemicals act as airborne signals. It compares receivers downwind of damaged senders in open air with receivers behind sealed barriers, so the receivers differ in whether air from damaged plants can reach them. The open-air receivers lose less tissue, linking air from damaged senders to stronger receiver defenses. Because every receiver gets the same number of caterpillars, fewer insects at the start can’t explain the lower leaf loss. Choice D.