The milk of many mammals contains cannabinoids, substances that are kn

Question

The milk of many mammals contains cannabinoids, substances that are known to stimulate certain receptors in the brain. To investigate the function of cannabinoids, researchers injected newborn mice with a chemical that is known to block cannabinoids from reaching their receptors in the brain. The injected mice showed far less interest in feeding than normal newborn mice do. Therefore, cannabinoids probably function to stimulate the appetite.

Which of the following is an assumption on which the argument depends?

A. Newborn mice do not normally ingest any substance other than their mothers' milk.

B. Cannabinoids are the only substances in mammals' milk that stimulate the appetite.

C. The mothers of newborn mice do not normally make any effort to encourage their babies to feed.

D. The milk of mammals would be less nutritious if it did not contain cannabinoids.

E. The chemical that blocks cannabinoids from stimulating their brain receptors does not independently inhibit the appetite.

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Official Answer

E

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KarishmaB · Accepted Answer

To know the function of Cs, researchers injected newborn mice with a chemical that is known to block Cs from reaching their receptors in the brain. 
The injected mice showed far less interest in feeding than normal newborn mice do. 
Therefore, Cs probably function to stimulate the appetite.

Researchers injected a chemical that blocks Cs. The injected mice stopped feeding. So we are concluding that Cs stimulate feeding. 
But what if the injected chemical is inhibiting feeding? Then our conclusion cannot hold. So we are assuming that the injected chemical does not inhibit feeding.

A. Newborn mice do not normally ingest any substance other than their mothers' milk.

Irrelevant. The argument is all about feeding. Injected mice showed far less interest in feeding than normal newborn mice do.

B. Cannabinoids are the only substances in mammals' milk that stimulate the appetite.

No we are not assuming that Cs are the only substances that stimulate appetite. Perhaps there are others too. We have seen a REDUCTION in appetite. Blocking Cs using a chemical is causing reduced appetite. So we are concluding that Cs do play some role in stimulating appetite.

C. The mothers of newborn mice do not normally make any effort to encourage their babies to feed.

Irrelevant. The point is about the interest of newborns in feeding.

D. The milk of mammals would be less nutritious if it did not contain cannabinoids.

Out of scope. We are not assuming anything about nutrition.

E. The chemical that blocks cannabinoids from stimulating their brain receptors does not independently inhibit the appetite.

Correct. As discussed before, we are assuming that the chemical we are injecting is itself not causing the reduction in appetite. The Cs may have no role in appetite if the chemical is the one causing reduction.

Answer (E)

olorin · Answer

E, I think.

I was initially thinking A. But settled on E as being the more correct answer. 

This is a trap by the testing methodology by throwing up a seemingly good answer at the beginning and saving the best answer for last - kinda testing whether your brain has grown tired...

Does anybody know whether the order of the options is randomized by the CAT or remains the same for a particular question?

HIMALAYA · Answer

B. Cannabinoids are the only substances in mammalsâ€™ milk that stimulate the appetite.

if other than Cannabinoids stimulates the appetite, the resercher would have not found chamically injected mice not having intreset in feeding.

anandsebastin · Answer

I disagree. Talking from a researcher's point of view, the mice would still have access to the mother's milk. A standard technique to study the actions of a substance is to block it using an inhibitor of the substance in study. One of the main concerns is the effects that the inhibitor may have by itself. So, E is the logical answer.

GMATBLACKBELT · Answer

E.

A: this was my contendor til I read E. But its weak.
B: this assumption is too extreme. 
C: irrelevant 
D: Irrelevant

E suggests that possibly the chemical was the cause. If this were the case the argument would be weakend. So E it is.

TooLong150 · Answer

My explanation:

E

Scenario
Two Groups of Mice
Group 1: the control group and had no chemical blocking cannabinoids.
Group 2: Had the chemical.

Result
Group 2 showed less interest in eating therefore cannabinoids function is stimulating appetite.

Negation of E: However, what if the chemical used in blocking cannabinoids by itself blocked the appetite? Then, this invalidates the experiment and thus the argument, and we can't say that cannabinoids stimulates appetite, because the chemical would be the one responsible for blocking the appetite.

Moderators, please change the OA to E according to Stacey's reply here: https://www.manhattangmat.com/forums/cr- ... -t682.html.

sameersanjeev · Answer

I got the correct answer. But I am still not exactly clear as to how can B and C be eliminated. Can someone please explain in simple language preferably with an example?

GMATNinja · Answer

When cannabinoids are blocked from reaching their receptors in the brains of injected mice, those mice show less interest in feeding. The author thus concludes that "cannabinoids probably function to stimulate the appetite." If that conclusion is valid, it would explain why appetite decreases when the cannabinoids are blocked.

The author concludes that cannabinoids probably stimulate the appetite but not that cannabinoids are the ONLY substances in mammals' milk that stimulate the appetite. For example, perhaps there are a couple other compounds in the milk that stimulate the appetite. Still, if one of those substances is blocked, we would expect appetite to decrease. Thus, the author's argument does not rely on choice (B).

Again, the author concludes that cannabinoids probably stimulate the appetite but not that cannabinoids are the ONLY factor affecting appetite. Perhaps mothers of newborn mice DO normally make efforts to encourage their babies to feed. Those efforts AND the cannabinoids could both serve to increase appetite. If either factor is removed, we would expect appetite to decrease. The author's argument does not rely on the assumption stated in choice (C).

I hope this helps! (And is anybody impressed that I refrained from making a dumb, obvious joke about cannabis and my home state of Colorado? I didn't think so...)

frrcattack · Answer

I solved this problem using the negation technique on answer choice E.

E. The chemical ... does not independently inhibit the appetite.

If we negate this answer choice, it would say that the chemical DOES independently inhibit the appetite. If that were the case, it would weaken our conclusion because ingesting the chemical would cause appetite loss regardless of how it affects cannabinoids. We would not be able to conclude that cannabinoids have an affect on appetite because the chemical causes appeite loss independently, which is something that would weaken our conclusion.

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jabhatta2 · Answer

Hi  avigutman   IanStewart  - i did get the answer but did have a followup. Same argument, one very small tweak

Question  - wouldnt in this case - B  also  be an assumption ?

sayantanc2k · Answer

No, from the part "far less interest" it cannot be inferred that there are other compounds (other than cannabinoids) that stimulate appetite. There may be factors other than compounds that stimulate appetite, for examle, voluntary activities such as running or involuntary activities such as beating of the heart. So even if the cannaboids are blocked, and they are the only appetite stimulant compound, the mice could still have some appetite remaining caused by factors other than compounds.

Only if you assume that compounds are the ONLY apetite stimulating factor, then your inference might be correct.

jabhatta2 · Answer

Thanks  sayantanc2k  - I had changed my original post completely but thank you for responding to the original post.

I think what you are saying is - from the below line

One cannot assume that there must be OTHER compounds that stimulate appetite. Perhaps Cannabinoid is still the ONLY compound that stimulates appetite(because  Running  could also stimulate appetite)

Regrding the yellow -- if we this additional assumption - compounds are the only appetite stimulants -- then maybe my inference (OTHER compounds other Cannabinoid must be stimulating appetite) is probably true.

avigutman · Answer

I would argue that such an inference is still a stretch even with the additional assumption. Here's the definition of "stimulate":
   raise   levels of physiological or nervous activity in (the body or any biological system)
 If there exists a base level of appetite which is greater than zero, your inference would be incorrect,  jabhatta2 .

sayantanc2k · Answer

Please see the explanation from  avigutman  above. Even with the additional assumption, we cannot infer that the apetite level is ZERO - we can at most assume that there is no increase in apetite. It is possible that there is always a base level of apetite irrespective of any stimulus, either from compounds or otherwise.

HarryGeorge · Answer

The argument presented in the passage is that cannabinoids probably function to stimulate the appetite. This conclusion is based on the observation that when newborn mice were injected with a chemical that blocks cannabinoids from reaching their receptors in the brain, they showed far less interest in feeding than normal newborn mice do.

Option E states that "The chemical that blocks cannabinoids from stimulating their brain receptors does not independently inhibit the appetite." This is an assumption on which the argument depends because if the chemical used to block cannabinoids independently inhibited the appetite, then the observed decrease in feeding behavior could be due to the chemical itself rather than the blocking of cannabinoids. In other words, if option E were not true, then the conclusion that cannabinoids probably function to stimulate the appetite would be weakened.

Option A states that "Newborn mice do not normally ingest any substance other than their mothers' milk." This is not an assumption on which the argument depends because even if newborn mice ingested other substances, it would not affect the conclusion that cannabinoids probably function to stimulate the appetite.

Option B states that "Cannabinoids are the only substances in mammals' milk that stimulate the appetite." This is not an assumption on which the argument depends because even if there were other substances in mammals' milk that stimulated the appetite, it would not affect the conclusion that cannabinoids probably function to stimulate the appetite.

Option C states that "The mothers of newborn mice do not normally make any effort to encourage their babies to feed." This is not an assumption on which the argument depends because even if mothers of newborn mice made efforts to encourage their babies to feed, it would not affect the conclusion that cannabinoids probably function to stimulate the appetite.

Option D states that "The milk of mammals would be less nutritious if it did not contain cannabinoids." This is not an assumption on which the argument depends because even if milk were less nutritious without cannabinoids, it would not affect the conclusion that cannabinoids probably function to stimulate the appetite.

VerbalBot · Answer

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The milk of many mammals contains cannabinoids, substances that are kn

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