Mice that have been given morphine are very likely to

This is what we need to weaken:

... naltrexone will turn out to be toxic to certain types of bacteria.

The researchers think that after naltrexone is administered, it kills the bacteria, and that is why there is no blood poisoning.

Option B tells us that what naltrexone actually does is just stop the effect that morphine has (triggering the migration of intestinal bacteria into the bloodstream). So the reason that there is no blood poisoning is not that the bacteria are dead, but that the bacteria are not migrating to the bloodstream.

This weakens the researchers’ prediction.

NischalSR

Conclusion:
Naltrexone will kill some types of bacteria.

(C) talks about giving N alone. It says that N does not increase the risk of developing blood poisoning. (They may have the same risk as without N or they may even have lower risk, we don't know. What we do know is that they do not have a greater risk of developing blood poisoning.)

Does it weaken that N is toxic to some bacteria? No. N could be toxic to some bacteria (lowering the risk of blood poisoning) or it may have no impact (the risk stays the same) on bacteria, we can't say. All we can say is that it doesn't increase the risk so it doesn't cause blood poisoning.
Hence (C) does not weaken our conclusion.

has to be B.

bacteria that normally reside in the intestine typically respond to morphine by migrating
into the bloodstream and cause blood poisoning. C is that N will be toxic to certain bacteria

Weaken

Look for choice that says N will NOT be toxic to intestinal bacteria. If N were to suppress the B-M interaction, blood poisoning would not occur and it cannot turn out to be toxic.

E says that some thing else causes BP. the conclusion here is more weakened by B by saying that N will not turn out to be toxic afterall.

p1 :- bacteria + morphine ==> blood cancer
P2 :- morphine + Naltrexone + Bacteria ==> less frequency of blood cancer
conclusion :- Naltrexone toxic for some bacteria

what if Naltrexone has no effect on Bacteria rather effect on morphine
B is the answer

Mice that have been given morphine are very likely to develop blood poisoning because
bacteria that normally reside in the intestine typically respond to morphine by migrating
into the bloodstream. However, when mice are given both morphine and the new drug
naltrexone, blood poisoning is much less frequent, although it does still occur. These
results provide support for researchers’ prediction that naltrexone will turn out to be toxic
to certain types of bacteria.

Which of the following, if discovered to be true, would most seriously weaken the
support for the researchers’ prediction?

The prediction is that naltrexone is toxic to bacteria since mice given morphine with naltrexone don't develop blood poisoning, normally caused by the intestine's response to morphine. To weaken this prediction one needs to find a different mechanism for naltrexone.
A. After being administered to mice, naltrexone does not pass from the bloodstream
into the intestine. Where naltrexone passes isn't relevant.
B. Naltrexone inhibits morphine from triggering the migration of intestinal bacteria
into the bloodstream.
C. Mice that have been given naltrexone but not morphine have no greater risk of
developing blood poisoning than do mice that have not been given either
substance. We already know that morphine induces blood poisoning. What occurs in the absence of morphine isn't relevant.
D. The increased risk of blood poisoning is not the only harmful effect on mice of
being given morphine. Anything other than blood poisoning is out of scope
E. Conditions other than the presence of intestinal bacteria in the bloodstream can
cause blood poisoning in mice. Other causes of blood poisoning are out of scope.

[quote="seofah"]Mice that have been given morphine are very likely to develop blood poisoning because bacteria that normally reside in the intestine typically respond to morphine by migrating into the bloodstream. However, when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur. These results provide support for researchers’ prediction that naltrexone will turn out to be toxic to certain types of bacteria.

Which of the following, if discovered to be true, would most seriously weaken the support for the researchers’ prediction?

A. After being administered to mice, naltrexone does not pass from the bloodstream into the intestine.
B. Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream.
C. Mice that have been given naltrexone but not morphine have no greater risk of developing blood poisoning than do mice that have not been given either substance.
D. The increased risk of blood poisoning is not the only harmful effect on mice of being given morphine.
E. Conditions other than the presence of intestinal bacteria in the bloodstream can cause blood poisoning in mice.



A. Incorrect. It is irrelevant to know the passage process of Naltrexone. It can still turnout to be toxic to certain type of bacteria
B. Correct. If this is true, then Nal. is not actually toxic to bacteria but inhibiting Mor. to make the reaction
C. Incorrect. Magnitude of the risk is irrelevant here. This simply doesn't help us evaluate whether Nal. is toxic to bacteria or not.
D. Incorrect. We don't care about other effects of Mor.
E. Incorrect. Again, we cannot infer from his whether Nal. is toxic to Bacteria or not.

Hope this helps!

But maybe the naltrexone just kills the bacteria before they migrate to the bloodstream. After all, the naltrexone could be given with the morphine (the argument simply says "mice are given both morphine and the new drug naltrexone"), and usually the migration occurs in response to the morphine.

As a critical side note, you cannot attack premises. Every premise on the GMAT is infallible! If you thought your answer worked by showing that a premise was untrue, then that should already have been a red flag.

B is correct because it shows how every premise could be true but the conclusion still would not follow, since there is a different reason for naltrexone's effectiveness.

You're taking C way too far by claiming that "C says that Naltrexone has no effect on its own."

All we know is that without morphine, the bacteria don't migrate from the intestine to the bloodstream. So maybe the bacteria remain in the intestine, where they don't cause blood poisoning, and where they never encounter naltrexone at all, and we have no way of knowing whether naltrexone would have been toxic to them. Or maybe the bacteria remain in the intestine, where naltrexone kills them all dead, but since they're not in the bloodstream they still wouldn't have caused blood poisoning. But none of this proves that naltrexone isn't toxic to any bacteria, and none of it weakens the argument.

The thing that, ultimately, your comment fails to explain is this: If, in fact, "Naltrexone has no effect of its own," then how does it, when taken with morphine, prevent blood poisoning that would otherwise occur with morphine alone?

"Naltrexone does nothing" is simply not a viable explanation to aim for here.

Explanation:

The argument states that naltrexone is harmful for many strains of bacteria. The evidence to support this conclusion is that when mice were given this new drug along with morphine, they had fewer cases of blood poisoning than they did in situations where the mice were given only morphine, which triggered harmful intestinal bacteria to mix with the blood of the mice. We need to prove that despite the reduction in the incidences of blood poisoning after the administration of the drug, the new drug has not damaging effect on the harmful bacteria.

Whether the new drug moves or not is irrelevant in knowing its effect on the bacteria.
CORRECT. As per this option, the new drug does not kill harmful bacteria. Rather, it only hampers the movement of these bacteria to the blood of the mice. Thus, whereas this new drug can be said to be good for the mice, since it prevents the cases of blood poisoning, it does not have a direct damaging effect on the harmful bacteria itself. This helps weaken the conclusion.
Mice which are given only the new drugs have the same chances of being bold poisoned. This will only prove the negative effect of the new drug on the mice. But this still does not clarify the relation between the new drug and the harmful bacteria.
We are not probing into the number of harmful effects of morphine.
‘Other causes of blood poisoning’ is again out of scope.

Can anybody explain why C is not a better answer than B.

@vertiaskarishma AjiteshArun
I rejected B because if Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream. How does it explain there is still blood poising there should have been no blood poising ?
Wouldn't it be extreme to consider that there are other ways to have blood poising because the passage doesn't say anything about that

Hi Experts

GMATNinja VeritasKarishma EducationAisle ChrisLele mikemcgarry AjiteshArun egmat sayantanc2k RonPurewal DmitryFarber MagooshExpert avigutman EMPOWERgmatVerbal MartyTargetTestPrep ExpertsGlobal5 IanStewart
other experts AnthonyRitz

I was confused between A and B and at last marked the wrong answer.

My thinking - When morphine is given then bacteria that reside in the intestine typically respond to morphine by migrating into the bloodstream. And option A says naltrexone does not pass from the bloodstream. So if bacteria is in bloodstream and naltrexone does not pass through it so how it will kill any bacteria and thus weakening the conclusion>

By assuming above things am I attacking the premise given in the passage "when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur"

That's why it's a wrong assumption ..Can you please answer to my query??

Thanks to all the experts!!!!

Hello KarishmaB and other EXPERTS

Can't we weaken the conclusion by establishing - Naltrexone will kill some will not kill any type of bacteria?
If so, C says that Naltrexone has no effect of its own and hence should be correct, right?

Please let me know where am I going wrong.

@GMATNinja

I didn't understand the question type. Isn't the question asking us to weaken the support and not the conclusion?

In my opinion, the support is that there is less frequency of blood poisoning when M and N are given as compared to when only M is given.

Yes, the support is "when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent."

Regarding the question type, this question is a Weaken the Argument question.

In general, in a Weaken question, the correct answer weakens the case for the conclusion. It does so by showing that, even though the facts presented are true, the conclusion may not be correct.

So, the correct answer does not indicate that the supporting premise may not be true. Rather, it may weaken the support provided by the premise.

For instance, in this case, the reasoning is that, since blood poisoning is less frequent when naltrexone is given, naltrexone must be toxic to the bacteria that would normally cause blood poisoning.

The correct answer shows that, even though blood poisoning is less frequent when naltrexone is given, naltrexone may not be toxic to bacteria since something else may be going on: it may be that naltrexone instead causes the bacteria not to migrate into the bloodstream.

So, the correct answer provides additional information that indicates that the conclusion may not follow from the premise. In other words, the correct answer weakens the support provides by the premise.

Thus, the correct answer is a classic Weaken correct answer.

Understanding the argument -
Mice that have been given morphine are very likely to develop blood poisoning because bacteria that normally reside in the intestine typically respond to morphine by migrating into the bloodstream. Opinion. Premise.
However, when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur. "however" introduces the contrast. Fact.
These results provide support for researchers’ prediction that naltrexone will turn out to be toxic to certain types of bacteria. - Conclusion. "naltrexone (N) will turn out to be toxic to certain types of bacteria." " N is toxic for bacteria."

Option Elimination -

(A) After being administered to mice, naltrexone does not pass from the bloodstream into the intestine. - We don't care how it passes into the intestine. It can still be toxic to bacteria. Out of scope.

(B) Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream. - Ok. So it says that the blood poisoning is less because N stops morphine from triggering the migration of bacteria and not because N is toxic to bacteria. This weakens.

(C) Mice that have been given naltrexone but not morphine have no greater risk of developing blood poisoning than do mice that have not been given either substance. - Essentially, it says N or no N, which has the same effect. But if N, it may still be toxic to bacteria. It doesn't weaken the scope of our argument. Out of scope.

(D) The increased risk of blood poisoning is not the only harmful effect on mice of being given morphine. - Effects of morphine are not the scope of our argument. Our argument is to weaken the conclusion that N is toxic to bacteria. Out of scope.

(E) Conditions other than the presence of intestinal bacteria in the bloodstream can cause blood poisoning in mice. - Other causes are out of scope.