A weaken question tests whether a finding makes a proposed explanation less likely. Read the proposal, put it in a few words, and split it into parts if it describes how something works. Ask what has to be true for each part to work, then predict a finding that would break a needed link. A finding weakens a proposal when it shows that a needed part may not hold. Sharing the topic isn't enough to challenge the proposal.
Hints
- Hint 1
Look at the group’s proposal in the second sentence. What role do the researchers give the red glow?
- Hint 2
Separate communication from secrecy. What must be true for members of the species to recognize one another using the glow, and what must be true for predators and prey to remain unaware of it?
- Hint 3
Trace the path from light being emitted to another fish recognizing the sender. Ask what has to happen in between.
Step-by-step
Trace the signal from sender to receiver
Step 1Split the proposal
The group proposes a secret communication signal between members of the species, and the question asks us to weaken that proposal. What does that use involve? The glow helps dragonfish recognize each other while keeping predators and prey unaware. A finding can weaken the proposal by challenging either of those parts.
- Step 2
Find what recognition needs
How could the glow help one dragonfish recognize another? The proposal points to photoreceptors able to detect this particular red wavelength; photoreceptors are cells that sense light. Sending a visual signal isn't enough; another member of the species has to detect it. A finding that separates giving off the light from sensing it would break a needed link in the proposal.
- Step 3
Test the findings
Do the findings about range, predators, or varying wavelengths directly challenge the proposed use? The glow could still work close up even if it blends into background light at distances greater than about 10 centimeters. Predators that detect red only at light levels much brighter than the glow wouldn't detect the signal at its actual brightness. Dragonfish could still detect fluorescence that varies substantially if their eyes sense a range of wavelengths, which the proposal doesn't rule out.
- Step 4
Question whether the fish can detect the glow
The finding that adult A. ruber photoreceptors respond weakly, if at all raises doubt about whether the fish can sense the glow. The fish may barely detect the light meant to help them recognize one another. That makes the proposed communication less likely, even if the glow stays hidden from predators and prey. Choice D.