Rats injected with morphine exhibit decreased activity of the immune

D is correct - If the immune system responses decreased after the morphine injections in this experiment, the hypothesis that it was by stimulation of the adrenal glands that morphine reduced immune-system activity would be undermined. But if no decrease in immune-system responses occurred, the hypothesis would be confirmed.

Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections. These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands. Since corticosteroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.

Which of the following experiments would yield the most useful results for evaluating the scientists’ hypothesis? < -- Evaluate Question

(A) Injecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids
- completely ignores any decrease in activity of the immune system -- that matters a lot here

(B) Testing the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats’ immune-system activity levels again
- where is morphine mentioned here? plays integral role in decreasing activity of the immune system

(C) Injecting rats with corticosteroids and then observing how many of the rats contracted infections
- same as "A"

(D) Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats’ immune-system responses
- correct as is

(E) Injecting rats with a drug that stimulates immune-system activity and then observing the level of corticosteroids in their bloodstreams
- same as "B"

idea here is that MORPHINE uses CORTICOSTEROIDS to REDUCE the immune response. since this is an EVALUATE question, we need something that can prove this idea.
> D = correct b/c if you remove the adrenal glands, how would the morphine stimulate corticosteroid growth to reduce the immune response?

Kudos please if you find this helpful

Stimulus
1) Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections. Morphine is bad for immune system
2) These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands. - Same rats--->exhibited heightened blood levels of "C"----->chemicals secreted by the adrenal glands.
3) Since corticosteroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.---------> morphine is by stimulating the adrenal glands to secrete "additional C" into the bloodstream

Question Stem:-
Required:-Which of the following experiments would yield the most useful results for evaluating the scientists’ hypothesis?

Option D is rightly attaining this objective - "Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats’ immune-system responses"

Analysis:- Some experiment which proves that morphine is NOT stimulating the adrenal glands. If adrenal glands are removed & if "additional C" is not present after injecting morphine then what does this explain. In fact morphine was stimulating the adrenal glands to secrete "additional C" into the bloodstream which was interfering with the immune responses of the rats.

jennpt - pls provide your feedback

Hi CAMANISHPARMAR

Overall, your notes and thought process look good. You have successfully identified that we need more information to prove the first link in the hypothesized "path": morphine -> stim. adrenals to make increased C -> increased C messes up immune system.
Just be careful that this is an Evaluate question stem, so we don't necessarily have to disprove it. Right now your Analysis notes look like this is a Weaken question.
However, we just want to get some info about whether the hypothesis could be right or wrong. So in your analysis note "Some experiment which proves that morphine is NOT stimulating the adrenal glands." ... I would just modify this to "Some data that describes WHETHER (IF) morphine is stimulating the adrenal glands."

Make sense?

Best, Jenn

in a causal argument, A appear when B appears. and the conclusion is A cause B.
we have many ways to weaken
1. B cause A, not A cause B
2. B dose not appear when A appear.
3. another thing cause B.

if we prethink, we can prethink one of above three. or at best, prethink all of three above
read choice D. D is match our prethink. if B dose not happen when A dose not happen, we have a strenthener. choice D is good.

evaluate question is similar to weakening question. we need to prethink the condition which fallsify argument before going to anserwer choices. the correct answer is the one which "potentially" weaken.

this is very hard problem because the prethink process dose not take us to the case " if A dose not appear, B dose not/dose appear, we have strengthen/weaken fact".

if prethinking dose not take us to a position which is close to the correct answer choice, the question is hard. if prethinking take us to the position close to the answer choice, the question is easy. gmat use statistics to realize which question is hard or easy and make the hard/easy questions.

Official Answer:

Argument Evaluation

Situation Rats injected with morphine exhibit decreased immune-system activity and increased levels of corticosteroids, which are secreted by the adrenal glands and can interfere with immune-system activity.

Reasoning What further experiment would help determine whether morphine reduces immune responses in rats by stimulating the adrenal glands to release more corticosteroids? Contrary to the scientists' hypothesis, the experimental results might have occurred because the morphine injections directly reduced immune-system activity. Or the injections might have blocked some mechanism that reduces corticosteroid levels in the blood, even if the morphine did not stimulate the adrenal glands to produce more corticosteroids. To evaluate whether the scientists' hypothesis is more plausible than these rival hypotheses, it would be helpful to know whether similar experimental results would occur after morphine injections even if adrenal gland activity did not change.

Option D is Correct. If the immune system responses decreased after the morphine injections in this experiment, the hypothesis that it was by stimulation of the adrenal glands that morphine reduced immune-system activity would be undermined. But if no decrease in immune-system responses occurred, the hypothesis would be confirmed.

Why option A, B, C & E are incorrect:-

A - Morphine could stimulate the adrenal glands of rats with normal corticosteroid levels to produce more corticosteroids, whether or not it does so in rats whose corticosteroid levels are already heightened.

B - Such an experiment would not involve morphine and thus would not help to determine how morphine affects immune-system activity in rats.

C - Whether or not rats contract infections may not reliably indicate their levels of immune-system activity.

E - Even if the mechanism by which a drug other than morphine increases immune-system activity were discovered, this discovery would not necessarily reveal the mechanism by which morphine reduces immune-system activity.

(A) Injecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids. This may prove that it produces additional corticosteroids but does not prove anything related to the immune system.

(B) Testing the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats’ immune-system activity levels again. While it sounds interesting to test the immune system and then remove their glands, this answer lacks the injection of morphine.

(C) Injecting rats with corticosteroids and then observing how many of the rats contracted infections. This may help explain that heightened levels of corticosteroids reduces the immune system but it does not explain the role played by morphine.

(D) Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats’ immune-system responses. So if we remove the glands and then inject with morphine what happens? hypothetically, no additional secretion of corticosteroids will be done and as a result the immune system responses will remain the same.

(E) Injecting rats with a drug that stimulates immune-system activity and then observing the level of corticosteroids in their bloodstreams.This talks about another drug that stimulate immune system activity but does not have an answer for the role of the glands.

3 things matter in this argument. Morphine, glands, and corticosteroids.

The argument states that scientists hypothesized that morphine simulates the glands to produce more corticosteroids and as a result reduce the immune system. We need something to check the validity of the argument.

Understanding the passage

Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections.
• When rats are injected with morphine, the activity of their immune system decreases.
• The immune system is the bodily system that fights off infections.
• Inference: Rats injected with morphine becomes more susceptible to infections.
These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands
• The rats which are injected with morphine also showed increased blood levels of corticosteroids.
• Corticosteroid is a chemical secreted by the adrenal glands in a body.
Since corticostebroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.
• Morphine stimulates the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream of the rats.
• Since corticosteroids can affect the immune system, scientists have come up with a hypothesis that morphine is responsible for the decreased activity of the immune system in rats.

Conclusion: Scientists hypothesized that morphine decreased the immune system activities by stimulating the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream.

Pre-thinking

Falsification Scenario

In what scenario – will morphine NOT decrease the immune system activities by stimulating the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream?

Given that:
(i) Rats injected with morphine show decreased activity of the immune system.
(ii) Rats injected with morphine also show increased blood levels of corticosteroids.
(iii) Corticosteroids are chemicals secreted by the adrenal glands.
(iv) Corticosteroids affect the immune system.

Though Process

Since rats, which are injected with morphine, showed decreased activity of the immune system and also showed increased blood levels of corticosteroids. And since corticosteroids are chemicals secreted by the adrenal glands which affect the immune system, scientists hypothesized that these elevated levels of corticosteroids are a result of the injected morphine.

Falsification condition: What if morphine is directly affecting the immune system even before additional corticosteroids are secreted into the bloodstream?
In this case, corticosteroids are not responsible for affecting the immune system because of morphine, which directly impacts and decreases the activity of the immune system. This condition would break down the conclusion.

Assumption: The morphine is not affecting the immune system directly even before additional corticosteroids are secreted into the bloodstream.
Answer choice analysis

(A) Injecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids INCORRECT
• If rats already have heightened blood levels of corticosteroids, then observing their new blood levels of corticosteroids will not prove whether stimulation of the adrenal glands are responsible for the decrease in the immune system activities after morphine is injected.

(B) Testing the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats' immune-system activity levels again INCORRECT
• The scientists hypothesize that morphine decreases immune system activities. This experiment does not involve morphine; therefore, this experiment is irrelevant.


(C) Injecting rats with corticosteroids and then observing how many of the rats contracted infections INCORRECT
• We already know that corticosteroids impact the immune system activities. The hypothesis is about how morphine impacts corticosteroid levels, which, in turn, impacts the immune system. This experiment does not involve morphine; therefore, it is irrelevant.


(D) Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats' immune-system responses CORRECT
• Variance test
o Yes – The level of the rats' immune-system responses decreases after removing the adrenal glands and injecting them with morphine.
o Since removing the adrenal glands ensure that additional corticosteroids are not secreted into the bloodstream, it would be clear to us that morphine is directly responsible for the decrease in immune system activities. This result would weaken the hypothesis of scientists.
o No - The level of the rats' immune-system responses did not decrease after removing the adrenal glands and injecting them with morphine.
o In this case, the hypothesis that corticosteroids and the adrenal glands are responsible for the decrease in the immune system activities is strengthened.

(E) Injecting rats with a drug that stimulates immune-system activity and then observing the level of corticosteroids in their bloodstreams INCORRECT
• This option proposes a reverse experiment that will not help us evaluate the hypothesis because this experiment will determine how the level of corticosteroids impacts the immune system activities and not how morphine impacts the adrenal glands, which in turn, impacts the immune system activities.

EducationAisle

Premise:
1) morphine = decreased activity of immune system
2) corticosteroids = interfere/disrupt immune system

Conclusion: Morphine --->corticosteroids ---> low immune system


Wouldn't (A) prove whether morphine leads to rise in corticosteroids? If corticosteroids rises then we can prove that indeed it is Morphine --->corticosteroids ---> low immune system


while (D) does work, why is (A) incorrect?

We need to prove the above conclsuion

The whole point is about conclusively establishing a correlation between heightened levels of corticosteroids and reduction in immune responses.

A does not address the issue of immune response at all!

Would the extremes test be applicable to this type of argument?
If so, how could it be applied to these AC's?

Amobnc

By "the extremes test," do you simply mean eliminating extreme answers? That's not something we can reliably do. It's more of a tendency. If a question is asking us to infer something, state the main point, find a statement the author would agree with, then we can rule out answers that are more extreme than what we have support for in the passage. However, we still have to know what is supported. If the data is extreme, the answer can be extreme! For instance, if the passage told us that EVERYONE loves chocolate cake more than vanilla cake, then we could conclude that vanilla is NOBODY'S favorite cake flavor.

In any case, here we are just presented with 5 different possible experiments, so there's nothing to make one more extreme than the other, unless you count what the poor rats have to go through. To get this right, we have to understand the hypothesis: that morphine brings about its immune effects via the adrenal gland. If rats WITHOUT adrenal glands are given morphine, that can be used to test whether those glands are really behind the effect in question.

­It sounds like you might be referring to the Variance Test from The PowerScore LSAT Logical Reasoning Bible: "The Variance Test consists of supplying two polar opposite responses to the question posed in the answer choice and then analyzing how the varying responses affect the conclusion in the stimulus."

That isn't so easy to apply in this case because the answer choices aren't simple yes or no questions. A better way to think about this one is: "For each experiment, would I expect one result if the hypothesis is right and a different result if the hypothesis is wrong?"

We're looking for an experiment that would yield DIFFERENT results in each of those two cases, and that's what we get in choice (D):

• Case 1, hypothesis is correct: In this case, morphine reduces immune responses in rats by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream. Without adrenal glands, this couldn't happen. So if we inject rats with morphine after removing their adrenal glands, we should NOT see decreased activity in their immune systems.
  
• Case 2, hypothesis is incorrect: In this case, the reduction in immune responses is caused by something else (not the adrenal glands). So if we remove the adrenal glands, we should still see decreased activity of the immune system in rats injected with morphine.

The results of the experiment described in (D) would be useful because we expect DIFFERENT results based on whether the hypothesis is wrong or right. The same cannot be said about the other choices, so (D) is the best one.

I hope that helps! ­