PT151 · S4 · Q22 Biologist: When bacteria

This is the classic "No cause, No effect" way to strengthen a causal story. Since the author thinks that chlorophyll is how the bacteria find the red light district, she would predict that if remove the chlorophyll, they will no longer be able to find the red light zone. That's just what this says, so it greatly strengthens her theory that the chlorophyll is involved in how they detect the red light.

It's unclear whether this answer is saying, "Given a test tube where red is an option, the bacteria show little inclination to visit any other color zones, even though they get more than no energy from those colors" or whether it's saying, "Even if you remove red from being an option, they show little inclination to move to the other color areas, which slightly energize them." If we're talking about a test tube where red is an option, this answer doesn't weaken at all. Red might be so energizing that these bacteria would be fools to visit any other color. If this is talking about a situation where red isn't an option, and they don't seem to be navigating towards the area of most energy, that would weaken the plausibility of the author's explanation a bit. It would start to look like maybe these bacteria aren't always seeking out the most chlorophyll energizing light. But it's also possible that these other colors aren't even energizing enough to register on the bacteria's radar. Some energy can still be an undetectable level of energy.

The author's explanation didn't seem to be making any assumptions about red being warmer. It wasn't warmth that was drawing the bacteria hither towards the red light; it was the amount of energy the bacteria's chlorophyll could harness from the light. We have no idea if that's connected to warmth in any way.

This feels like maybe it weakens plausibility as well, by providing evidence of Effect w/o Cause. This answer describes bacteria moving towards areas lit by certain colors of light (the Effect) even though they don't have chlorophyll (which was involved in the Cause). There are a couple reasons why this isn't the best answer, though: 1. Other species of bacteria that don't contain chlorophyll are likely to be pretty significantly different from those that do (plants have chlorophyll; animals don't). So whatever those bacteria are doing with their lives probably isn't that great to compare to our bacteria. They may have there own reasons for preferring certain colors of light and their own ways of navigating there. Consider this analogy -- Jack read Tina's LSAT Guide and did well on the LSAT, so someone concludes 'Jack did well by following the advice in Tina's LSAT Guide.' Which one makes you doubt that more? (D) Jill read Tina's Guide and followed its advice to the same level Jack did, and she did terribly on the LSAT. (Cause w/o Effect) (E) Jasmine did not read Tina's Guide, but she still did well on the LSAT (Effect w/o Cause) 2. The reason this answer has unclear impact is because we don't even know if the bacteria with non-chlorophyll actually all moved to the same color of light. The description is wishy-washy, like "sure, if you put them into a test tube, they move into areas lit by particular colors of lights". Yes, but do they all move to the same color light and stay put? If not, then this isn't really even a comparable case to the bacteria with chlorophyll that we're analyzing.