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

Question

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

AndrewN · Accepted Answer

This post is a response to those by  guarav2m  and  willacethis  above. Now, let me preface my post by saying that I am a native speaker of American English, so I cannot know how hard such a passage may be to tackle if I were a second-language learner of English. With that said, neither I nor most native speakers I know would find this passage easy to navigate (read as something that I would choose to peruse and enjoy on my own). Yes, there is a bunch of jargon, and yes, the passage is lengthy, with sentence after sentence about scientific-sounding chemicals and processes.

To overcome the language barrier, one of my students employed a strategy of reading everything that looked technical as its leading letter instead. So, for instance, a word such as  adenosine  would simply be  A . In this manner, he could comb through the passage pretty efficiently and know where to look to find the information to a question asking about  A .

As for my own approach, I take nothing more than mental notes as I go. I pay attention to the authorial presence or bent regarding the information presented, and I also look to follow what I call the transition trail from line to line or paragraph to paragraph. For example, if you see a line that starts with  nevertheless , you understand, without going any further, that the information that is about to come is going to follow in a  despite    or  even so  vein. I also look for emotionally charged words or strong language, such as  must  (from the beginning of paragraph two in this passage), so that I can follow the tenor of the passage even without taking in all the information on offer. Finally, when it comes to detail-based, according-to-the-passage questions, I match keywords from the question stem to what I can locate in the passage. I refer to the passage a lot when I answer RC questions. My timing is still fine across any given set, and, most importantly, my accuracy is high. I do not overburden my mind with details, since I know GMAT™ questions are nuanced anyway, to the point that relying on memory alone will often lead to incorrect answers on more difficult passages. One or two words in the answer choices might be all that separates those answers from what the passage actually says, and that can make all the difference.

I hope that helps at least a little. One more thing about timing: If you know your timing across other types of Verbal questions comes in under 1:48 or so on average, then you might be able to take a bit more time reading through passages and processing the question stem and answer choices. Just stick to the above, and, with practice, you will grow more confident as your results improve.

Good luck with your studies.

- Andrew

daisywei · Answer

This passage took me 20 minutes to read. :shock:

Here is my understanding of the passage. #1. S.D.B. came up with a hypothesis that caffeine affects behavior by doing the opposite of what adenosine (ade) does. #2. S.D.B. further explain how that works. Because caffeine is structurally similar to ade, it can prevent ade from attaching A1&A2 and allows more neuron firing. #3. S.D.B. refute the previous view that caffeine affects behavior by stop producing phosphodiesterase(pho). It will need more caffeine concentrations to do that. #4. S.D.B. strengthen their hypothesis by citing an experiment. They conclude that the higher the compounds’ capacity to bind at the receptors, the higher the compounds’ ability to stimulate behavior. (Theophylline is such a compound.) #5. S.D.B. argue that although there are some compounds don’t show that kind of correlation mentioned in #4, their hypothesis is still valid.

GMATNinja · Answer

Check out the  Ultimate RC Guide for Beginners  for tips on how to approach RC passages like this one!

rulingbear · Answer

8. The passage suggests that Snyder et al believe that if the older theory concerning caffeine’s effects were correct, which of the following would have to be the case?

I. All neurotransmitters would increase the short-term concentration of cyclic AMP in target neurons.

II. Substances other than caffeine that inhibit the production of phosphodiesterase would be stimulants.

III. All concentration levels of caffeine that are high enough to produce stimulation would also inhibit the production of phosphodiesterase.

(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II, and III

This is the concerned paragraph

"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. "

So this paragraph is saying 2 distinct things and we are looking for scenarios that will question the Snyder team's conclusion.

1. Yes, caffeine may inhibit the production of phosphodiesterase which in turn leads to stimulation, however, stimulation will occur before you get to the level required for the aforementioned inhibition.

This is negated by III - All concentration levels of caffeine that are high enough to produce stimulation would also inhibit the production of phosphodiesterase.

2. Compounds can impede the activity of phosphodiesterase without being stimulants.

This is negated by II - Substances other than caffeine that inhibits the production of phosphodiesterase would be stimulants.

Hence, II & III are would be true if the old theory were true. Hence D.

Statement I - "All neurotransmitters would increase the short-term concentration of cyclic AMP in target neurons" is simply irrelevant to the question and out of scope we are concerned with the path that caffeine and other compounds take to effect stimulation and whether the inhibition of an enzyme is that path. The role of neurotransmitter is simply intermediate and would occur regardless.

I hope this helps.

RMD007 · Answer

So here is the question -- Okay. So we have to weaken the claim proposed by Snyder et al Lets take these options one by one - This does not weaken the claim. In the last paragraph author says that caffeine can have mixed effects at low concentrations and this behavior is OK . Even if this is true, it claims that caffeine at low levels stimulates the mouse locomotion. This is also in line with Snyder et al 's explanations. Okay, if the said concentration of Cyclic AMP is produced by several others as well caffeine, it does not weaken any claim by Snyder et al Snyder et al claims that caffeine dislodges adenosine from its receptors and that results in greater neuron firing. Thereby produces behavioral stimulation in humans. So it is a series of dependent events. But if the concentration of caffeine that is required to dislodge adenosine to produce behavioral stimulation is much greater, then probably this behavioral stimulation is not caused by dislodging of adenosine. This breaks the reasoning chain. These are independent events; does not deduce anything. Hope it helps...

Will2020 · Answer

Here is the OA for the first six questions (OG 10th):

1. D is the best answer.

This question requires you to identify the primary concern of the passage as a whole. The first paragraph presents a recent hypothesis about how caffeine affects behavior. The second paragraph describes an earlier and widely accepted hypothesis about how caffeine affects behavior, and then presents evidence that is not consistent with that hypothesis. The third and fourth paragraphs return to the newer hypothesis introduced in the first paragraph and provide “evidence and arguments” that support this alternative hypothesis.

2. D is the best answer.

Lines 11-23 state that adenosine “depresses neuron firing” by binding to specific receptors on neuronal membranes, which in turn inhibits the release of neurotransmitters. Lines 27-35 describe Snyder et al’s hypothesis about caffeine. They propose that caffeine binds to specific receptors on neuronal membranes, which prevents adenosine from binding to those receptors and “allows the neurons to fire more readily that they otherwise would”. Therefore, according to Snyder et al, caffeine differs from adenosine in that caffeine permits neurotransmitter release when it is bound to adenosine receptors, whereas adenosine inhibits neruotransmitter release.

3. A is the best answer.

The effects of IBMX are discussed in the last paragraph of the passage. IBMX apparently binds to adenosine-specific receptors on neuronal membranes, but, in contrast to the other caffeine derivatives that Snyder et al experimented with, IBMX depresses rather than stimulates mouse locomotion. Snyder et al respond to this experimental result by stating that IBMX has “mixed effects in the brain, a not unusual occurrence with psychoactive drugs”(line 104-107)

4. E is the best answer.

This question asks you to identify which compound, according to Snyder et al, does NOT bind to specific receptors in the brain. Phosphodiesterase, identified as an “enzyme that breaks down the chemical called cyclic AMP”(lines 40-42), is the only compound that is not identified as one that binds to specific receptors in the brain.

5. B is the best answer.

This question asks you to identify information that is suggested rather than directly stated in the passage. To answer it, first look for the location in the passage of the information specified in the question. The A1 and A2 receptors are mentioned in lines 23-26. Lines 27-35 go on to describe Snyder et al’s hypothesis about the effects of caffeine on behavior. They propose that caffeine, “which is structurally similar to adenosine,” is able to bind to A1 and A2 receptors in the brain, the same receptors that adenosine normally binds to. Thus, the passage suggests that the structural 311 relationship between caffeine and adenosine may be partially responsible for caffeine’s ability to bind to A1 and A2 receptors.

6. B is the best answer.

This question asks you to identify the function of a quotation in the third paragraph of the passage.

The third paragraph provides evidence for Snyder et al’s hypothesis by discussing experiments they conducted on mice. The quotation in lines 74-84 “summarizes” the findings of these experiments. Snyder et al found that a number of caffeine derivatives are able to bind to specific receptors in the brains of mice just as adenosine does, and that the derivatives that are most successful at stimulating locomotion are also the most successful in competing with adenosine in binding at the receptors. This finding is “major” in that it supports their hypothesis that the simulative effects of caffeine are a result of its ability to compete with adenosine.

adkikani · Answer

MentorTutoring   VeritasKarishma   SajjadAhmad

Can you help to explain how OA to Q4 can be E? We already established the difference between adenosine and caffeine in Q2.

Cross out the compounds that bind with specific receptors in brain, the one that remains is answer.

Furthermore, see below relevant passage:

This is an opinion, not a fact

This clearly states that caffeine is able to bind with specific receptors but adenosine is not.

KarishmaB · Answer

The first two paragraphs clarify that caffeine and adenosine, both attach to receptors.

... Snyder, Daly, and Bruns have recently proposed that caffeine affects behavior by countering the activity in the human brain of ... 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.

So normally, adenosine attaches to the receptors and inhibits the release of neurotransmitters. But when caffeine is ingested, it binds to both receptors which prevents adenosine from attaching. Hence, neutrons fire more readily.

AndrewN · Answer

Hello,  adkikani . If you need to answer a question about  binding , then you should look for the keyword  bind  in the passage, particularly because the frame of the question, as an EXCEPT, lets you know that you are looking for a detail. How about we approach the task, answer by answer?

Analysis: The last paragraph states that IBMX   bound  very well  in the context of  adenosine  receptor binding  and stimulation . You might be able to kill two birds with one stone here and cross off (C) as well, but if you were being extra careful, at least you could get rid of this answer choice.

Analysis: Paragraph two states that  Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to  bind  to both types of receptors . Yes, this is a  proposal  rather than a statement of fact, but look at the question again:  According to Snyder et al.  This answer cannot be argued against.

Analysis: If the two previous analyses did not convince you that adenosine can bind to receptors in the brain, then I am not sure how many instances you need from the passage to convey the point. The first such instance is from the beginning of paragraph two:  adenosine must first  bind  to specific receptors on neuronal membranes . Three strikes and you're out.

Analysis: The highlighted portion of paragraph four draws attention to theophylline, which  was one of the most effective  compounds  in both regards . Which regards, exactly? One of them is spelled out with an  id est :  the higher their capacity to  bind  at the receptors . Thus, theophylline is not our answer.

Analysis: The process of elimination points to this odd one out, without even a check. However, in the interest of providing a full analysis, what does the passage say about phosphodiesterase? The appositive phrase attached to the word in paragraph three tells us:  an enzyme that breaks down the chemical called cyclic AMP . The rest of the paragraph talks about this enzyme, but nowhere will you find the keyword  bind .

I have said it before, and I will reiterate here: keep your approach simple. The more you delve into the semantics or possibilities of each answer choice, the harder the test is going to be for you. Stick to the surface.

- Andrew

gaurav2m · Answer

i really needed help to solve such informative passages as it takes too much time to write every information of the passages.
even if you write the relations.still you have to come back to the passage if there are too much inference questions.

VeritasKarishma  /  GMATNinja  /  daagh  /  egmat .

willacethis · Answer

Dear experts

I understand that one is not required to focus on every detail in a passage and is required, in the first read, to get a gist of the structure of the passage and where significant details can be located in the passage.

However, when I saw such overwhelming amount of details, I got lost in the middle and even though I could gather some idea about the purpose and structure, I was not able to retain most of the complex terms, and thus, ended up feeling lost whenever I read a detail question.

Considering this scenario, could you please help me in understanding how to go about such a passage? I was not too fast while I read the passage. I almost took 5:20 minutes just to read the passage.

GMATNinja · Answer

This is a long passage with a ton of details, and there's no magic bullet for getting better at them. Check out our  RC guide for beginners  for tips on how to approach RC passages like this one. You might also get some mileage out of  this video  that covers some common reasons why test-takers struggle on RC (and CR).

I hope that helps a bit!

GMATNinjaTwo · Answer

In these cases, you want to double down on the approach you described: read for structure and purpose, don’t obsess over details.

When struggling with a dense and complex passage, students tend to panic and "get lost in the weeds" trying to understand/absorb all of those complex terms and details. Instead, take a step back, don't worry if you are having trouble with some of the confusing details, and focus on getting through that passage with a sense of the overall structure and purpose. Then, if needed, you can always revisit certain parts of the passages if you are asked about some of the details that you missed.

I know that isn't very satisfying, but I hope it helps!

You might also find  this post  helpful.

MBAB123 · Answer

For question 2, perhaps citing the exact place where the answer (Option D) lies might help.

1. Caffeine (last sentence of the 2nd paragraph- "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."

2. Adenosine (2nd to last sentence in the 1st paragraph) - "Adenosine normally depresses neuron firing in many areas of the brain."

I'm happy to help further if needed.

Sajjad1994 · Answer

Official Explanation

1. The primary purpose of the passage is to

Difficulty Level:   700

Explanation

A.  The passage discusses a current investigation, not one planned for the future.

B.  The passage examines two explanations, but the earlier theory is discussed only to expose its weakness and the differences between the explanations are not reconciled. Most of the passage is devoted to the more recent hypothesis.

C.  Only two theories are presented in the passage.

D.  Correct.   The recent hypothesis provides an alternative to an earlier one and is supported by evidence and arguments.

E.  Lines 32–37 do pose such a challenge to the earlier theory; however, the challenge is a small part of the whole passage. Similarly, in the final paragraph, an exception to the more recent theory is introduced, only to be dismissed as an unimportant concern.

The correct answer is D.

6. The author quotes Snyder et al.  in lines 43–48 most probably in order to

Difficulty Level:   700

Explanation

A.  The quotation explains the results of an experiment, not assumptions about a theory.

B.  Correct.   The quotation summarizes the experiment with mice and reports a major finding in support of the hypothesis.

C.  The quotation generalizes on the basis of the experiment; it does not limit the finding to mice.

D.  Specific, not general, correlations were made between the ability to bind to receptors and to stimulate locomotion.

E.  The passage includes no such objections; therefore no refutations are needed.

The correct answer is B.

KittyDoodles · Answer

Hi Experts,

GMATNinjaTwo 
 GMATNinja 
 KarishmaB

I have read the above explanations for Q6 and I'm still not able to figure out why the option is B and not A.

I thought the assumption is "the ability of the compounds to compete at the receptors correlates with locomotion." Thus, this is how caffeine causes stimulation.

I'm still not able to understand how is it a finding of an experiment.

Thanks
Kitty

RonTargetTestPrep · Answer

This problem follows GMAC's typical pattern:  The more technical detail there is in the text, the LESS important it is for you to understand those details specifically.

In fact, all you really need to figure out the role of the quote is to notice the verb with which it's presented:
 "..., they  reported "

What, from a scientific experiment, would you  report ? You'd report the findings of the experiment. (You could e.g.  list  or  mention  assumptions made in the experimental design, but it wouldn't make any sense to say that you were 'reporting' assumptions.)

If you  do  comprehend what's stated in the quote, then you can notice that a  statistical correlation  is being reported ("the higher X is, the higher Y is as well").
Correlations come from data, which must be the results of the experiment (not its assumptions or anything else).

hrusher · Answer

Q5 structural similarity(identical) vs structural relationship(between two objects, can be similar or different) got me wrong, how can one say both are same.
Q1 primary purpose: blank on that question, lost in such long RC... can anybody help how to reach the PP?

GMATNinja · Answer

Question 5 
 
Regarding Q5, let's start by considering the following key points from the passage:

According to Snyder, caffeine "affects behavior by countering the activity in the human brain of...adenosine."   Adenosine normally creates its effect by "inhibiting the release of neurotransmitters."   Adenosine normally binds to receptors A1 and A2.   "Caffeine, which is  structurally similar to adenosine , is able to bind to both types of receptors..." (i.e. A1 and A2).

Let's now consider answer choice (C):

The passage does talk about a structural similarity. However, it tells us that caffeine is similar to  adenosine , not too  neurotransmitters . Notice adenosine inhibits the release of neurotransmitters, so adenosine itself is not a neurotransmitter. Eliminate (C).

Let's now consider (B):

As you suggest, the word "structural relationship" doesn't  necessarily  mean similarity. It  could  mean similarity, or it could mean some other type of relationship.

That being said, the passage does suggest that caffeine's ability to bind to A1 and and A2 is related to its structural similarity to  adenosine . And if two structures are similar, you could say they have a "structural relationship."

So while (B) doesn't specify that the structures are similar exactly, it's still a true statement: the structural relationship between caffeine and adenosine (i.e. in this case, the fact they have similar structures) helps explain why caffeine can bind A1 and A2. For that reason, (B) is correct.

Question 1 
 
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!

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

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GMAT Reading Comprehension (RC) Questions

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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