Insects can see ultraviolet light and are known to identify important

Hi,

I am not an expert but a learner. Still, I would explain my reasoning. In fact, Option “D” weakens the argument. We need to strengthen the argument by showing that it’s the UV light pattern that attracts insects whereas in “D” though both the webs reflect UV light but insects are attracted to only one web which means the reason for the attraction is not UV light but something else. This weakens the argument.

Hope this helps. Thanks!

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Insects can see UV light. They sense the pattern of UV reflected by things to identify them (food sources etc). So say if a certain insect eats a certain plant, the pattern in which the plant reflects UV light will be observed by the insect and that will help it identify which plant it is.

Insects are attracted to G webs, which reflect UV.

Conclusion: Insects are probably attracted to these webs because of the specific patterns of ultraviolet light that these webs reflect.

So perhaps spiders make G webs in a way that they reflect UV in a certain pattern which attracts insects (say insects think that it is their food source). Hence spiders are able to catch insects in the web to eat.

What supports the conclusion?
We already know that G webs reflect UV light. We need to support that it is the pattern in which they reflect UV light that attracts insects.

(A) When webs of many different species of spider were illuminated with a uniform source of white light containing an ultraviolet component, many of these webs did not reflect the ultraviolet light.

Other webs that don't reflect UV are irrelevant.

(B) When the silks of spiders that spin silk only for lining burrows and covering eggs were illuminated with white light containing an ultraviolet component, the silks of these spiders reflected ultraviolet light.

Knowing that other webs reflect UV is not enough. Do they reflect UV in the same pattern as G webs? Do insects get attracted to their webs too?

(C) When webs of the comparatively recently evolved common garden spider were illuminated with white light containing an ultraviolet component, only certain portions of these webs reflected ultraviolet light.

Same logic as (B).

(D) When Drosophila fruit flies were placed before a Glomosus web and a synthetic web of similar pattern that also reflected ultraviolet light and both webs were illuminated with white light containing an ultraviolet component, many of the fruit flies flew to the Glomosus web.

Both G web and synthetic web had the same pattern of UV reflection. Still, many flies few to G web. This suggests that something other than UV pattern attracted them to the G web. If at all, it could weaken our conclusion.
But the use of "many" is anyway questionable. Did many flies fly to synthetic web too? We don't know. Hence this option is useless.

(E) When Drosophila fruit flies were placed before two Glomosus webs, one illuminated with white light containing an ultraviolet component and one illuminated with white light without an ultraviolet component, the majority flew to the ultraviolet reflecting web.

Two G webs - one illuminated with UV light and one illuminated without UV light. If most flies flew to the one illuminated with UV light, it does seem that the UV light pattern is responsible for attracting flies. The web that did not reflect that UV pattern did not get any/many flies.
Strengthens our conclusion.

Answer (E)

Hi ,


My two cents


Here the Conclusion just talks about the Web Glomosus and UV reflection pattern. Not the Pattern of Web itself .
In D , the two webs are of similar pattern ( may be the design is similar ) but not the UV reflection pattern

So D is incorrect .

E is the only option left .

hope this helps .

Yes sir, i am also referring to the pattern of the ultraviolet rays emitted by the real web vs synthetic web. Since the flies are able to differentiate between the two, this strengthens the argument.

Am I missing something?

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D weakens the argument because the synthetic web is similar in every way to the Glomosus web. It also emits the same patterns so the flies can't differentiate between the 2 patterns. The conclusion states that its because of the patterns the flies flock to the Glomosus web but D shows that since the patterns for the synthetic and the Glomosus webs are the same,the flies gravitate towards the Glomosus for a different reason in strengthening causal reasoning we need to prove the cause the conclusion or argument states not deny it. E does that

Hi VeritasKarishma can you please help here b/w D and E.

I selected D because of following reasoning:
The argument says that insects are probably attracted to these webs because of the specific patterns of ultraviolet light that these webs reflect. Option D says that when both Glomosus and synthetic webs (of similar pattern) were illuminated by UV light many of the flies flew to Glomosus web. My line of reasoning to select this was, given both are UV light Glomosus web exhibit specific patterns to which flews are drawn.

While with E one Glomosus web is UV lit and another is not and flies flew to the one that was UV lit, but what about the specific pattern. The argument says that insects are drawn to specific pattern which are identified in UV light Insects can see ultraviolet light and are known to identify important food sources and mating sites "by sensing the characteristic patterns" . Since, the other Glomosus web was not lit by UV the insects were drawn to the one with UV and that has already been mentioned in the argument. So how does this supports the conclusion?

VeritasKarishma Thanks for your explanation, I see now what I lacked in understanding the argument.

Conclusion: UV reflection by Glomosus webs --> insect attraction.
Premises: Glomosus webs reflect UV. Insects are attracted to Glomosus webs.

There is a clear causal element to the conclusion. The argument has taken the two facts and inferred a causal link. In order to strengthen that, we will want to explore things like whether there's some other cause, whether the relationship is reversed, and whether it might just be coincidence. The odds in this case are on "some other cause" or "coincidence," as "reversed" doesn't make any sense (the webs don't reflect UV because insects are attracted to them).

Let's look at the answer choices:

(A) I think we expected that to be the case. Does nothing to explain why insects are attracted to THIS web. Eliminate.

(B) Maybe insects are attracted to those webs, too. So what? Or maybe insects stay away from those webs because those webs don't resemble a food source or a mating site due to the lining burrow and eggs. Either way, so what? Does nothing to explain why insects are attracted to THIS web. Eliminate

(C) Maybe insects are attracted to those webs, too. So what? Or maybe insects stay away from those webs because those webs don't resemble a food source or a mating site due to some other characteristic. Either way, so what? Does nothing to explain why insects are attracted to THIS web. Eliminate.

(D) If anything, this would WEAKEN the argument. It seems to suggest that the UV reflectivity is not the deciding factor in attracting insects. The attraction seems to be from some other characteristic of THIS web. Eliminate.

(E) Wait, so you're telling me that the exact same webs, one that's reflecting UV light and one that's not, attract insects differently? UV light seems to matter!

Answer choice E.

While question is trying to seek the strengthener for a specific patter of UV, the correct answer choice E points to the presence and absence of UV. This looks erroneous .

Are you taking the word pattern to mean that there are different patterns of UV light independent of what they are reflecting off of? If so, I'm not sure I see that in the argument or answer choices.

The pattern is determined by the specific thing that light (UV or otherwise) reflects off of.

E gives us the opportunity to show that it is not the pattern alone but the pattern in combination with UV that matters.

Bro, I think that could also be the reason that insects are not merely attacted to UV reflections as both natural one and artificial one are emitting UV lights. Doesn't it conclude in some way that there might be some pattern in UV reflection that these natual webs were reflecting compared to the artificial one.

Hi KarishmaB

As per your explanation for option D, i think you have assumed the similar reflective pattern of UV light of both G Web & S Web. While the sentence says that both G Web & S Web have a similar web pattern that also reflects UV light.

I am reasonably certain that the test maker implied that the S web also emits UV in the same pattern as G web does since the S web has the same pattern as the G web. We know that light is reflected as per the pattern of the object so there isn't any distinction to be made between the two.
It makes sense that an option will tell us that both webs had similar pattern of UV but the insects were attracted to G web. This would weaken the argument and would be used as a trap option.