LordStark wrote:
Insects can see ultraviolet light and are known to identify important food sources and mating sites by sensing the characteristic patterns of ultraviolet light that these things reflect. Insects are also attracted to Glomosus spiderwebs, which reflect ultraviolet light. Thus, insects are probably attracted to these webs because of the specific patterns of ultraviolet light that these webs reflect.
Which one of the following, if true, most strongly supports the argument?
(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.
(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.
(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.
(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.
(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.
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)