The chemical adenosine is released by brain cells when those cells are

Brain cells release Ade when people are awake.
Ade binds to more and more cells at this time.

When asleep, these bindings reduce.

Hypothesis - The large number of bindings cause sleepiness.
(When the bindings increase too much, the brain signals that we need to sleep to reduce the bindings)


(A) Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large.

We are talking about relative number of bindings. Bindings increase when awake and reduce when asleep. Whether the absolute number is small or large while we are asleep is irrelevant.

(B) Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.

Caffeine interferes with bindings (does not let Ade bind to cells) and is known to cause wakefulness. This does strengthen that a large number of bindings cause sleepiness. When caffeine is ingested, it interferes with bindings and hence would lead to wakefulness if bindings cause sleepiness.


(C) Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.

Irrelevant

(D) Some areas of the brain that are relatively inactive nonetheless release some adenosine.

Irrelevant

(E) Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.

This is irrelevant too. It does not help us link sleepiness to bindings. This tells us that stress can preserve wakefulness even if bindings are high. Then it does not strengthen that bindings cause sleepiness.

Answer (B)

Hypothesis is 'cumulative binding of adenosine to a large number of sites that causes the onset of sleep'. Choice B provides evidence that caffeine interfers with binding of chemical to sites on brain cells and also that caffeine prevents sleep. This provides support to hypothesis.

Ans B it is.

The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases. Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep. Which of the following, if true, provides the most support for the researchers’ hypothesis?

A. Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large.
It just says that even during sleep, adenosine remains bound to large number of brain cells... does not help in argument

B. Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
correct.. this tells us that caffine keeps people awake and interferes in binding

C. Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.
out of context

D. Some areas of the brain that are relatively inactive nonetheless release some adenosine.
again out of context

E. Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.
again out of context
ans B

Conc: cumulative binding of adenosine to a large number of sites causes the onset of sleep.

We need to strengthen this causal argument. There are several way you can strengthen a causal argument. You can suggest that whenever cause happens effect happens. No cause no effect. effect did not cause the cause and so on.

B is correct as it says no cause no effect. i.e. No cumulative binding of adenosine(because of caffeine) no sleep.

I actually thought A as OA as somehow high binding causes sleep.
I am not getting any connection b/w B and hypothesis to be supported.

Why?

Question is a strengthen question. With that in mind, the conclusion of the stem says "Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep." Even if you don't read anything else, what would strengthen this statement? The only choice that does not weaken it or is out of scope, and actually does strengthen it, is B because the conclusion says that it is the large binding of the chemical that promotes sleep. If anything interferes with it and keeps people awake, it strengthens the argument because the it supports that the chemical does indeed induce sleep.

Just to add to the discussion on top.
The argument is using cause and effect reasoning.

Conclusion: Cause (i.e. cumulative binding of adenosine to a large number of sites) -> Effect (i.e. Sleep)

Strengthener: No Cause (Caffeine interferes with the binding of adenosine to sites on brain cells) -> No Effect (No sleep = Wakefulness)
Therefore, answer is B.

No doubt that Option B supports the argument but Option E also states that sleep preserves wakefulness even when the brain levels of bound adenosine are high which implies that high levels of adenosine cause the onset of sleep and stress counters it. How can we say that E is out of context?

Posted from my mobile device

As you state, E informs us of a counter effect to anedosine. it is perhaps true that this is not entirely out of context, but it definitely doesn't strengthen the claim that andeosine causes sleep, which is what we are looking for. It's just informing us about the existence of an opposite force- and at that, only one which operates in very specific conditions (danger). so, no support here.

I don't fully see how you can simply say "out of context" without articulating why it's out of context.

I narrowed it down to B and E, but went with E.

Both B and E infer that Caffeine and Stress preserve wakefulness.

I really needed to understand the OG explanation to see why E was wrong and well, E actually confirms that Stress impedes the sleep inducing effect of adenosine - It doesn't "refute the hypothesis".

Speaking of which, I didn't jot this down before I answered the question, which is probably why I marked it incorrect.

Conclusion/ Hypothesis: The cumulative binding of adenosine to many sites causes the onset of sleep

Back to E - E is incorrect because it neither refutes nor validates this conclusion/hypothesis. We want something that STRENGTHENS.

B - Coffee induces wakefulness and inhibits binding of adenosine to sites on brain cells. So it is then logical to infer that because coffee inhibits binding, people remain awake and so if adenosine was bound to brain sites people would be asleep.

I found this tough to get my head around under timed conditions.

Understanding the stimulus itself is a challenge for this one. Isn't the hypothesis of the researchers against premises - that binding of adenosine causes wakefulness, instead of the onset of sleep? Thanks for clarifying.

acc. to you
"adenosine binds to more and more sites on cells in certain areas of the brain" creates wakefulness

acc. to me what you got is opposite of what is stated.
if you read it you will find: As the total amount released gradually increases during wakefulness, adenosine then binds to more and more sites on cells in certain areas of the brain.

there is a cause and effect situation, but you got a reversal of it.

Thanks = KUDOS

My 2 cents on this question:
Premise : The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases.
Conclusion : 'the cumulative binding of adenosine to a large number of sites'(A) that causes 'the onset of sleep'(B)

Given we have a causal argument here, the standard assumptions are:
1) There are no other reasons
2) It's not a coincidence.

Now, the question asks us to strengthen the conclusion, so our answer should do the following things:
1) Offer evidence to show that it is not a coincidence.
2) Get rid of other factors that might cause B
3) Provide examples of the cause being present and the effect following. If A happens, then B happens.
4) Show that if A does not happen then B also does not happen.

Now, coming to the options
(A) Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large. - Out of scope. Keep the predicted answer in your mind.

(B) Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells. - Bingo, this is in line with the 4th strengthener that we discussed. If Caffeine is in the system, a person remains wakeful(B is not happening i.e. the effect is not happening). Why is the effect not happening because the cause i.e. 'increased cumulative binding' is not happening because of the caffeine. This is also a classic example of contrapositive. If not B -> not A

(C) Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body. - Irrelevant

(D) Some areas of the brain that are relatively inactive nonetheless release some adenosine. - Irrelevant

(E) Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high. - Irrelevant

Hope it helps

Still not convinced
how B strengthens the argument?
Cumulative binding cause to sleep, however for caffeine it interferes with with the binding of adenosine to sites on brain cells.
I found no connection on this two

Hey junii, see if this helps
1. Binding leads to sleep.
2. Caffeine interferes with binding and it is known to cause wakefulness (lack of sleep).

The option is basically saying that caffeine restricts sleep by interfering with the binding process (and hence supporting the argument that binding leads to sleep). Of course, this does not prove that the argument is bulletproof. But we are not really looking to prove that, we're just trying to support the argument and the option does just that.

Can someone please explain in detail why A is wrong?

The passage tells us about a cycle that occurs within the brain:

• When you've just woken up: you don't have as much adenosine
• Throughout the period of wakefulness: cells gradually release more and more adenosine
• This adenosine binds to brain cells.
• During sleep: the adenosine decreases.

... and then the cycle continues. Based on this, the researchers think that the cumulative binding of adenosine causes the onset of sleep.

Take a look at (A):

(A) tells us that, even at the low point, there is a lot of adenosine in the brain. This doesn't impact the cycle described above -- perhaps the "baseline" level of adenosine is high, but throughout the day it gets 100 times higher.

The researchers care about the amount of adenosine in one part of the cycle relative to the amount of adenosine in another part of the cycle. (A) tells us about an absolute amount of adenosine at one point in the cycle, which really doesn't impact the author's argument. If anything, the hypothesis depends on adenosine being lower in the middle of the night, so the information in (A) could somewhat weaken their evidence.

So you can eliminate (A).

I hope that helps!