PrepTest 151, Section 4, Question 22
Biologist: When bacteria of a particular species are(71 more words not shown)
Which one of the following,(7 more words not shown)
- AIf the chlorophyll(29 more words not shown)
- BThe bacteria show(30 more words not shown)
- CThe areas of(25 more words not shown)
- DThe bacteria show(35 more words not shown)
- EThere are species(29 more words not shown)
Reading the argument
Red light gives these bacteria more energy. But how do they recognize the red light?
Perhaps they respond to a temperature difference. Perhaps they have some other way of detecting the color. Those are possibilities, not facts about this species. The point is that moving toward the color that produces energy efficiently doesn't yet tell us that the bacteria measure the energy production to find it.
What we’re looking for
The biologist proposes that specific mechanism. To weaken it, I'd look for evidence that the movement depends on something else, or that the bacteria don't move as the energy-monitoring explanation would lead us to expect.
Working the answers
- A
Removing chlorophyll also removes the preference for the red areas. That connects the chlorophyll with the behavior and supports, rather than undermines, the proposed explanation. It doesn't prove exactly how detection works, but it moves in the wrong direction for this question.
- B
Producing some energy from another color doesn't make that color equally useful. The passage says this shade of red permits more effective energy production. Avoiding other colors that produce less energy is compatible with the idea that energy production guides the bacteria. B doesn't give the mismatch we need.
- C
This works against the particular alternative that the bacteria simply seek a warmer red area. It doesn't supply evidence against energy monitoring. Also, 'no warmer, on average' doesn't mean every area's temperature is identical or rule out every conceivable response to temperature. The relevant point is that C hasn't shown a competing mechanism behind the red preference.
- DCorrect
Now the blue areas produce as much energy as the red ones, yet the bacteria still don't tend to move into them. If the bacteria identified their destination by how much energy chlorophyll was producing, why would these equally productive areas fail to attract them?
The continued difference in behavior despite equal energy production makes that explanation less convincing. We don't have to identify the actual detector or prove that energy plays no role whatsoever. D gives a specific result the proposed monitoring mechanism doesn't readily explain.
- E
Other species may use different ways of detecting light. Showing that bacteria without chlorophyll respond to colors doesn't establish how this species, which has chlorophyll, does it. We need evidence against the explanation of these bacteria's behavior, not merely evidence that another mechanism exists somewhere else.
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