Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth.” Snyder, Daly, and Bruns have recently proposed that caffeine affects behavior by countering the activity in the human brain of a naturally occurring chemical called adenosine. Adenosine normally depresses neuron firing in many areas of the brain. It apparently does this by inhibiting the release of neurotransmitters, chemicals that carry nerve impulses from one neuron to the next. Like many other agents that affect neuron firing, adenosine must first bind to specific receptors on neuronal membranes. There are at least two classes of these receptors, which have been designated A1 and A2. Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would. For many years, caffeine’s effects have been attributed to its inhibition of the production of phosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP. A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons. Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation. But Snyder et al. point out that the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation. Moreover, other compounds that block phosphodiesterase’s activity are not stimulants. To buttress their case that caffeine acts instead by preventing adenosine binding, Snyder et al. compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge adenosine from its receptors in the brains of mice. “In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.” Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most effective compounds in both regards. There were some apparent exceptions to the general correlation observed between adenosine receptor binding and stimulation. One of these was a compound called 3-isobutyl-1-methylxanthine (IBMX), which bound very well but actually depressed mouse locomotion. Snyder et al. suggest that this is not a major stumbling block to their hypothesis. The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones. 1 1. The primary purpose of the passage is to (A) discuss a plan for investigation of a phenomenon that is not yet fully understood (B) present two explanations of a phenomenon and reconcile the differences between them (C) summarize two theories and suggest a third theory that overcomes the problems encountered in the first two (D) describe an alternative hypothesis and provide evidence and arguments that support it (E) challenge the validity of a theory by exposing the inconsistencies and contradictions in it 2 2. According to Snyder et al., caffeine differs from adenosine in that caffeine (A) stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only (B) has mixed effects in the brain, whereas adenosine has only a stimulatory effect (C) increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations (D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release (E) inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing 3 3. In response to experimental results concerning IBMX, Snyder et al. contended that it is not uncommon for psychoactive drugs to have (A) mixed effects in the brain (B) inhibitory effects on enzymes in the brain (C) close structural relationships with caffeine (D) depressive effects on mouse locomotion (E) the ability to dislodge caffeine from receptors in the brain 4 4. According to Snyder et al., all of the following compounds can bind to specific receptors in the brain EXCEPT (A) IBMX (B) caffeine (C) adenosine (D) theophylline (E) phosphodiesterase 5 5. Snyder et al. suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to which of the following? (A) The chemical relationship between caffeine and phosphodiesterase (B) The structural relationship between caffeine and adenosine (C) The structural similarity between caffeine and neurotransmitters (D) The ability of caffeine to stimulate behavior (E) The natural occurrence of caffeine and adenosine in the brain 6 6. The author quotes Snyder et al. highlighted ] in lines 43–48 most probably in order to (A) reveal some of the assumptions underlying their theory (B) summarize a major finding of their experiments (C) point out that their experiments were limited to the mouse (D) indicate that their experiments resulted only in general correlations (E) refute the objections made by supporters of the older theory

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Caffeine, the stimulant in coffee, has been called the most widely us

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GMATNinja

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28 May 2024, 12:11

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Question 6

Question 6 asks why the author included the following quotation from Snyder et al. (which just means "Snyder and others") in the passage:

Quote:

"In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.”

To understand why the author includes this quotation, first think through the structure of the passage as a whole. In the first two paragraphs, the author explains Snyder's idea about how caffeine works. In the third paragraph, the author discusses a different, older idea about how caffeine works.

The quotation that we care about happens in the fourth paragraph. In this paragraph, the author gives Snyder et al. a chance to explain why they are right and the older idea is wrong. Snyder performed an experiment in mice, and from this experiment concluded something that is true "in general." In other words, in this quotation, they show the broader finding that they extrapolated out of their experiment.

So, which answer choice captures this best? Does the quotation:

Quote:

A. reveal some of the assumptions underlying their theory

Nope, the quotation reveals a finding of an experiment, NOT an assumption underlying the theory. (A) is out.

Quote:

B. summarize a major finding of their experiments

This seems to be on track! The quotation is there to quickly explain what Snyder et al. found in their experiments. Keep (B) for now.

Quote:

C. point out that their experiments were limited to the mouse

Sure, the experiments were done on mice -- but this quotation is actually a broader statement about how caffeine works in general. The purpose of the quote isn't to point out limitations of the experiments, but rather to explain a finding of the experiments. Eliminate (C).

Quote:

D. indicate that their experiments resulted only in general correlations

The word "only" stands out here. Is the author trying to minimize the experiments by saying, "well, they ONLY resulted in general correlations..."?

Not at all! The words "in general" here actually makes these experiments more applicable to situations outside the mice. The author includes the quotation to help Snyder et al. make their case, not to minimize the importance of the experiments. (D) is out.

Quote:

E. refute the objections made by supporters of the older theory

Snyder et al. certainly disagree with an older theory. But we haven't seen any "objections" from people who support the old theory -- they haven't been given a chance to weigh in on Snyder's new theory at all. So, the quotation can't be refuting such objections.

We can eliminate (E), and (B) is the correct answer to question 6.

I hope that helps!

arthurchichester

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06 Jul 2024, 12:20

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Could you please explain a strategy on how to go about question 1. I solved the passage in under 6mins having only the first one wrong, I was so confused in the language of the last 3 options that I marked one (E) randomly and moved ahead.

I do get stuck in main point questions but only in RC and not in CR.

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29 Jul 2024, 15:33

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arthurchichester

For tips on identifying the primary purpose of this passage, check out this video, which analyzes this passage in detail and goes through several of the questions, including question 1.

For general pointers on how to identify the primary purpose, check out our RC guide for beginners or this RC video playlist.

I hope that helps a bit!

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06 Apr 2026, 22:59

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GMATNinja

hi can you tell me if such extreme long passages can come in the exam because it took me 3 mins just to read the passage

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07 Apr 2026, 00:45

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Legallyblond

GMATNinja

hi can you tell me if such extreme long passages can come in the exam because it took me 3 mins just to read the passage

It can come in exam and takuing 3 mins to read such a long passage is perfectly fine.

All the best!!

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07 Apr 2026, 11:37

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hi can you tell me if such extreme long passages can come in the exam because it took me 3 mins just to read the passage

bhanu29 is correct: passages of this length are fair game on the GMAT, though this is one of the very longest we've seen in the official materials. You're not terribly likely to see anything quite this long on your exam -- and if you do, the rest of your RC passages will almost certainly be shorter.

If it takes you three minutes to read a passage of this length, that's fine. Usually, a super-long passage would have four questions attached to it on the exam. Since you're given an average of nearly two minutes per question on the verbal section, three minutes on the passage is fine -- if you read the passage well, you'll be efficient on the questions that follow, and can hopefully slice through them in less than five minutes.

I hope that helps a bit!

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