Explanation for 73.4.20 (glutamate)

tjphilbricktjphilbrick Alum Member
edited January 2017 in Logical Reasoning 174 karma

73.4.20 https://7sage.com/lsat_explanations/lsat-73-section-4-question-20/

This is a phenomenon-hypothesis Strengthening question, so we are looking for an answer choice that strengthens the hypothesis or an answer choice that prevents an outside factor from weakening the hypothesis.
The passage is basically saying that the process goes like this: When nerve cells are damaged after a stroke, glutamate can leak from them and can kill other nerve cells. We are left to reasonably presume that this is included in the definition of continuing nerve cell deterioration. Therefore glutamate is present in blood of those whose nerve cells continue to deteriorate after a stroke.
Answer choices (it came down to C and D):
A – incorrect because saying that any neurotransmitter that leaks from damaged nerve cells will damage other nerve cells does not strengthen the relationship we want. It doesn’t give us any more reason to think that glutamate in particular is impacting surrounding nerve cells.
B – incorrect because it’s irrelevant
C – This was very hard to eliminate, but it is incorrect for a couple of reasons. 1) Knowing that it is the only one that leaks from damaged nerve cells doesn’t necessarily impact the relationship. If it does, we have to stretch it with a bit assuming in order to do so (for instance, you have to assume that it actually DOES leak from those nerve cells). 2) It doesn’t rule out the possibility that glutamate could come from five billion other locations in the body. It therefore definitely does not strengthen the statement that glutamate from damaged nerve cells is a cause of brain damage. Just because it is the only neurotransmitter that leaks from oxygen-starved or damaged nerve cells does not mean that it only leaks from those nerve cells. In fact, it leaves the door wide open to think that it could leak from a long list of other places, and we know from the stimulus that we don’t care about those other places. We just want to know if leakage from oxygen-starved or damaged nerve cells causes brain damage, and this answer choice doesn’t give us enough security and clarity for us to be able to do that.
D – This is the correct answer, because it specifies that glutamate can ONLY come from damaged or oxygen-starved nerve cells. This enables us to say (or at least makes it possible for us to say) that glutamate very well could cause brain damage/long-term nerve cell deterioration, since the way it can get into the blood stream in the first place is from oxygen-starved or damaged nerve cells.
E – incorrect because 1) we don’t need to know anything else about nerve cells to conclude that glutamate causes brain damage, and 2) it doesn’t matter that they can leak glutamate and still survive intact. This has no impact on the relationship we are trying to strengthen, since if they were destroyed, it wouldn’t do us any harm or any good.

[Admin edit: replaced with link to question. Please don't post full questions, thanks!]

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