Passage Summary: Bacteria like to hang out in red light, and they happen to have a chemical that turns that exact red light into energy. Because of this coincidence, a scientist thinks the bacteria find the light by sensing how much energy they are making.

Conclusion: Bacteria likely detect specific red light by monitoring the amount of energy their chlorophyll produces.

Reasoning: Bacteria move toward a specific shade of red light that their chlorophyll uses most efficiently to produce energy.

Analysis: The biologist is jumping from a correlation to a cause. Just because the bacteria move toward the light that gives them the most energy doesn't mean the *energy production* is the signal they use to find it. To weaken this, we should look for an answer that suggests the bacteria have a different way of sensing the light, or that they still move toward the light even when energy production is not happening. If they can find the light without the energy 'sensor' working, the biologist's theory falls apart.