Question 196·200 Super-Hard SAT Reading Questions·Information and Ideas
Deep-sea biologists have observed that the dragonfish Asteropterus ruber emits red biofluorescent light, an unusual trait because red wavelengths are rapidly absorbed in seawater. One research group proposed that this red glow functions as a secret communication signal between members of the species: they suggest that only A. ruber individuals possess photoreceptors able to detect this particular red wavelength, allowing them to recognize one another without alerting predators or prey.
Which finding, if true, would most directly weaken the group’s proposal?
For weaken/strengthen questions, identify the claim and the one or two assumptions it must rely on. Then pick the option that most directly attacks (for weaken) or supports (for strengthen) one of those assumptions, and ignore choices that merely add context or create a minor complication without undermining a requirement.
Hints
Restate the scientists’ idea in your own words
Describe what the research group thinks the red glow is for, and what must be true about the dragonfish’s vision for that idea to work.
Focus on the key assumption
What must be true about A. ruber’s ability to detect that red wavelength for the glow to function as communication?
Look for a direct contradiction
The best weakening evidence will directly clash with a necessary condition of the proposal (not just add an interesting detail).
Step-by-step Explanation
Identify the claim and its required assumption
The group claims the red fluorescence is a secret communication signal because only A. ruber can detect that specific red wavelength.
A required assumption is that A. ruber actually can detect the red-fluorescence wavelength with its photoreceptors.
Check which option attacks that assumption most directly
Evaluate each option by asking whether it directly challenges the idea that the fish can use the red light as a visual signal.
- The fluorescence fading into the background beyond about 10 cm limits range, but it could still work at close range.
- Predators detecting red only at intensities far brighter than the dragonfish’s glow doesn’t show predators can detect the dragonfish’s actual signal.
- Variation in peak wavelength could complicate signaling, but it doesn’t show the fish can’t detect the light or that signaling is impossible.
Choose the option that contradicts the fish’s ability to see the signal
If lab measurements show adult A. ruber photoreceptors respond weakly, if at all, to the red-fluorescence wavelength, then the fish likely cannot reliably see the light it produces. That directly weakens the proposal.
Answer: Laboratory measurements show adult A. ruber photoreceptors respond weakly, if at all, to the red-fluorescence wavelength.