PrepTest 102, Section 2, Question 10
Insects can see ultraviolet light and are known(51 more words not shown)
Which one of the following,(7 more words not shown)
- AWhen webs of(28 more words not shown)
- BWhen the silks(29 more words not shown)
- CWhen webs of(25 more words not shown)
- DWhen Drosophila fruit(41 more words not shown)
- EWhen Drosophila fruit(34 more words not shown)
Reading the argument
Is it the pattern of light that attracts the insects, or just the ultraviolet light itself?
The passage gives us a plausible connection. Insects use ultraviolet patterns to identify food sources and mating sites. These spiderwebs also reflect ultraviolet light, and insects are attracted to them. Perhaps the webs resemble something the insects normally want to approach.
But I don't yet know that the particular pattern is doing the work. Maybe the amount of reflected ultraviolet light matters more. The insects' attraction is a fact; the proposed reason for it needs support.
For a strengthener, I'd like a comparison that changes the pattern and checks whether insect behavior changes too.
What we’re looking for
If otherwise similar webs drew different responses when their patterns differed, that could help distinguish the proposed explanation from attraction to ultraviolet light more generally. Let's see how close the choices get to that evidence.
Working the answers
- A
Some other species' webs don't reflect ultraviolet light. But what do insects do around those webs? Without information about their response, this fact doesn't connect reflection with attraction, much less show that the specific pattern explains the response to Glomosus webs.
- B
This concerns silk used for lining burrows and covering eggs. Learning that such silk reflects ultraviolet light doesn't tell us what draws insects to Glomosus webs. Reflection alone isn't the behavioral connection the argument needs.
- C
Only certain parts of a garden spider's web reflecting ultraviolet light could produce a pattern. But the answer still doesn't tell us how insects respond to it. A fact about the distribution of reflected light is not yet evidence that that distribution attracts insects.
- D
Both webs reflect ultraviolet light and have a similar pattern. Many flies going to the Glomosus web doesn't tell us how many went to the synthetic one or establish a preference between them. Even if we did learn they preferred Glomosus, we'd need to ask what other difference caused that preference, since the patterns are similar. D doesn't isolate the pattern as the source of attraction.
- ECorrect
The comparison keeps both webs Glomosus webs but changes whether the illuminating light contains ultraviolet light. Most flies approach the web that can reflect that ultraviolet component. That supports ultraviolet reflection playing a role in attracting them.
This doesn't fully answer my initial question about the precise pattern. The experiment compares ultraviolet light with no ultraviolet light, not one pattern with another. Still, it supplies relevant evidence for the proposed explanation, whereas the other choices don't connect the relevant change with insect behavior. Strengthening the argument doesn't require proving every detail of its explanation.
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