Weaken problem--Caterpillar

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Weaken problem--Caterpillar

by amysky_0205 » Thu Jan 17, 2013 1:28 am
Certain genetically modified strains of maize produce a natural insecticide that protects against maize-eating insects. The insecticide occurs throughout the plant, including its pollen. Maize pollen is dispersed by the wind and often blows onto milkweed plants that grow near maize fields. Caterpillars of monarch butterflies feed exclusively on milkweed leaves. When, in experiments, these caterpillars were fed milkweed leaves dusted with pollen from modified maize plants, they died. Therefore, use of the modified maize inadvertently imperils monarch butterflies.

Which of the following, if true, most seriously weakens the argument?

A. Per unit of volume, the natural insecticide produced by the genetically modified maize plants is less toxic to insects than are many commercial insecticides commonly used on maize plants.
B. Standard weed-control practices that have been used by farmers for decades have largely eliminated milkweed plants from certain areas where monarch-butterfly caterpillars were once common.
C. The experiments showed that the caterpillars were not harmed by contact with the pollen from the genetically modified plants unless they ingested it.
D. The maize-eating insects that the natural insecticide protects against do not feed on the pollen of the maize plant.
E. Airborne maize pollen tends to collect on the middle leaves of milkweed plants and monarch caterpillars feed only on the plant's tender upper leaves.

OA: E

can someone explain?????
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by Jim@StratusPrep » Thu Jan 17, 2013 5:39 am
E is correct because even though the pollen is lethal to the butterflies, they will not come in contact with it because the feed on different parts of the plant than where the pollen will be found.
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by ceilidh.erickson » Thu Jan 17, 2013 12:39 pm
Whenever you want to weaken a CR argument, you have to find the logical flaw. What information is missing between the given premises and the conclusion?

Premises:
- certain GM strains of maize produce insecticide
- insecticide is found in pollen, which often blows onto milkweed
- monarch caterpillars feed on milkweed leaves
- in experiments caterpillars fed milkweed dusted with pollen died

Conclusion:
- use of GM maize imperils monarch butterflies

So what information is missing here?
- Certain strains of GM maize produce insecticide, but does all modified maize imperil monarchs?
- Were the conditions in lab experiments the same as in nature? What if caterpillar-growing-season and pollen-dispensing-season were two different times of year? Or what if, for some other reason, caterpillars did not actually eat the pollen in nature? That would weaken the conclusion.

In answer E, if pollen collects in the middle of leaves and caterpillars eat only the edges, then the conditions of the experiment were not comparable to conditions in nature, so the conclusion does not hold.
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by kumarsaravana » Wed Jan 07, 2015 5:34 am
omeone please explain !!!

" Caterpillars of monarch butterflies feed EXCLUSIVELY on milkweed leaves "

Which could mean that caterpillar's feed is LIMITED TO MILKWEED LEAVES.

If caterpillars have to LIVE, obviously they have to eat ONLY MILKWEED LEAVES all day all season, since caterpillar's feed is LIMITED TO MILKWEED .

How Option C is right ?

Also please explain in option C , How "actively feeding" is different from "feeding" in the context.

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by [email protected] » Fri Jan 09, 2015 4:16 pm
Hi kumarsaravana,

The correct answer is actually E, not C.

The logic in the prompt is "causal" (meaning something causes something else to happen). It argues that the maize pollen (with insecticide in it) lands on milkweed leaves and caterpillars will eat these leaves and die. This result was generated in experiments and is used to prove the conclusion that using the modified maize puts monarch butterflies in danger.

The prompt as us the WEAKEN the argument, so we're looking for an answer that will damage the causal argument. The correct answer points out that while monarch caterpillars DO each milkweed leaves, they eat the part of the leaves that does NOT have the maize pollen on it.

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by VivianKerr » Wed Jan 14, 2015 3:07 pm
I think Rich might be confusing this problem with a similar GMAT OG 15 question. Also a good one! :-)

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