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

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Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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Updated on: 03 Aug 2019, 03:33
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Quote:
Part of New RC Series- Please check this link for more questions

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. 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

Spoiler: :: OA
D

Spoiler: :: OE
71. 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 diff erences 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. Th e 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.

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

Spoiler: :: OA
D

Spoiler: :: OE
72. A. The passage does not suggest that adenosine stimulates behavior.
B. While the final paragraph reveals that caffeine displays mixed eff ects, the passage does not state that adenosine has a stimulatory effect.
C. Increasing cyclic AMP concentrations is part of the earlier theory, not that of Snyder et al.
D. Correct. Lines 17–21 explain that caffeine binds to the receptors, releasing neurotransmitters, whereas adenosine hinders that release.
E. Inhibiting the production of phosphodiesterase is discussed in the earlier theory, not in the work of Snyder et al.

The correct answer is D.

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

Spoiler: :: OA
A

Spoiler: :: OE
73. A. Correct. The results of one experiment can be explained by mixed eff ects in the brain, which Snyder et al. say may occur with psychoactive drugs.
B. This response refers back to the earlier theory, not to Snyder et al.’s response concerning IBMX experiment results.
C. Caffeine is only included within the broad category of psychoactive drugs.
D. This effect is attributed to one compound,IBMX, not to all psychoactive drugs.
E. This ability is not discussed in the passage.

The correct answer is A.

4. According to Snyder et al., all of the following compounds can bind to specifi c receptors in the brain EXCEPT

(A) IBMX
(B) caffeine
(C) adenosine
(D) theophylline
(E) phosphodiesterase

Spoiler: :: OA
E

Spoiler: :: OE
74. A. Lines 54–55 state that IBMX binds to receptors.
B. Lines 17–19 state that caff eine binds to receptors.
C. Lines 13–14 state that adenosine binds to receptors.
D. Lines 46–50 state that theophylline binds to receptors.
E. Correct. The passage includes no evidence that phosphodiesterase binds to receptors.

The correct answer is E.

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

Spoiler: :: OA
B

Spoiler: :: OE
75. A. Phosphodiesterase is discussed in an entirely diff erent context in lines 22–25.
B. Correct. Lines 17–19 suggest that caffeine’s structural similarity to adenosine may be responsible for its ability to bind to A1 and A2 receptors.
C. Caff eine acts on neurotransmitters; it is not structurally similar to them.
D. Caffeine’s ability to stimulate behavior results from, rather than causes, this process.
E. The passage does not discuss the natural occurrence of these compounds.

The correct answer is B.

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

Spoiler: :: OA
B

Spoiler: :: OE
76. A. The quotation explains 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.

Which of the following, if true, would most weaken the theory proposed by Snyder et al?

(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

Spoiler: :: OA
D

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

Spoiler: :: OA
D

The last paragraph of the passage performs which of the following functions?

(A) Describes a disconfirming experimental result and reports the explanation given by Snyder et al in an attempt to reconcile this result with their theory.

(B) Specifies the basis for the correlation observed by Snyder et al and presents an explanation in an attempt to make the correlation consistent with the operation of psychoactive drugs other than caffeine.

(C) Elaborates the description of the correlation observed by Snyder et al and suggests an additional explanation in an attempt to make the correlation consistent with the older theory.

(D) Reports inconsistent experimental data and describes the method Snyder et al will use to reanalyze this data.

(E) Provides an example of the hypothesis proposed by Snyder et al and relates this example to caffeine’s properties.

Spoiler: :: OA
A

Originally posted by surat on 17 Feb 2004, 05:10.
Last edited by SajjadAhmad on 03 Aug 2019, 03:33, edited 11 times in total.
Updated complete topic (53).
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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19 Dec 2017, 17:38
3
gmatexam439 wrote:
Hi,

Please can you throw some light on question 8!

Regards

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.
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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12 Jul 2017, 20:55
2
This passage took me 20 minutes to read. 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 <Theo> 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.
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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29 May 2018, 21:10
2
shrupk wrote:
Hello,

Can somebody please explain Q7?

Thanks.

So here is the question --

Quote:
Which of the following, if true, would most weaken the theory proposed by Snyder et al?

(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

Okay. So we have to weaken the claim proposed by Snyder et al

Lets take these options one by one -

Quote:
(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

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.

Quote:
(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

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.

Quote:
(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

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

Quote:
(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

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.

Quote:
(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

These are independent events; does not deduce anything.

Hope it helps...
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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09 Jun 2018, 21:25
2
RMD007 wrote:
shrupk wrote:
Hello,

Can somebody please explain Q7?

Thanks.

So here is the question --

Quote:
Which of the following, if true, would most weaken the theory proposed by Snyder et al?

(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

Okay. So we have to weaken the claim proposed by Snyder et al

Lets take these options one by one -

Quote:
(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

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.

Quote:
(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

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.

Quote:
(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

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

Quote:
(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

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.

Quote:
(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

These are independent events; does not deduce anything.

Hope it helps...

Thanks RMD007 for the awesome explanation!

As noted by gmatexam439 several months ago (sorry gmatexam439, didn't see your question before!), questions #7-9 do not appear to be official questions. These three are not included in the OG or in the Verbal Reviews, so I wouldn't worry too much about them.

JAIN09, note that these 3 additional questions obviously skewed your timing data.

Thanks everybody!
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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11 May 2019, 01:50
1
Took me 14min 19sec to answer all the questions (including reading) and got all correct.

I have been solving a lot of RC passages lately and what I have observed is that I am pretty comfortable with passages (no matter what the difficulty level is) from topics such as science, technology, biology, psychology or business but struggling with passages from humanities background. Can anyone share some similar experience and how did he/she overcome that barrier.

GMATNinja any expert advice?

Regards
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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05 Jul 2017, 21:22
kivalo wrote:
Please add timers to the OP.

How do you approach passage like this one on the first read?
Do you just understand the structure and then move on to the questions or do you try to understand the relationships immediately? I thought I could skim over details but the questions proved me wrong .

Check out the Ultimate RC Guide for Beginners for tips on how to approach RC passages like this one!
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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19 Dec 2017, 18:38
gmatexam439 wrote:
Hi,

Please can you throw some light on question 8!

Regards

Thanks rulingbear for the explanation! Also, questions 7-9 don't appear to be official questions. It is possible that they appeared in the 10th edition (and if somebody has a copy, please take a look!), but the 2015 and 2016 Verbal Reviews only contain the first 6 questions for this passage.
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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10 Apr 2019, 13:17
surat wrote:
Quote:
Part of New RC Series- Please check this link for more questions

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. 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

Spoiler: :: OA
D

Spoiler: :: OE
71. 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 diff erences 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. Th e 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.

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

Spoiler: :: OA
D

Spoiler: :: OE
72. A. The passage does not suggest that adenosine stimulates behavior.
B. While the final paragraph reveals that caffeine displays mixed eff ects, the passage does not state that adenosine has a stimulatory effect.
C. Increasing cyclic AMP concentrations is part of the earlier theory, not that of Snyder et al.
D. Correct. Lines 17–21 explain that caffeine binds to the receptors, releasing neurotransmitters, whereas adenosine hinders that release.
E. Inhibiting the production of phosphodiesterase is discussed in the earlier theory, not in the work of Snyder et al.

The correct answer is D.

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

Spoiler: :: OA
A

Spoiler: :: OE
73. A. Correct. The results of one experiment can be explained by mixed eff ects in the brain, which Snyder et al. say may occur with psychoactive drugs.
B. This response refers back to the earlier theory, not to Snyder et al.’s response concerning IBMX experiment results.
C. Caffeine is only included within the broad category of psychoactive drugs.
D. This effect is attributed to one compound,IBMX, not to all psychoactive drugs.
E. This ability is not discussed in the passage.

The correct answer is A.

4. According to Snyder et al., all of the following compounds can bind to specifi c receptors in the brain EXCEPT

(A) IBMX
(B) caffeine
(C) adenosine
(D) theophylline
(E) phosphodiesterase

Spoiler: :: OA
E

Spoiler: :: OE
74. A. Lines 54–55 state that IBMX binds to receptors.
B. Lines 17–19 state that caff eine binds to receptors.
C. Lines 13–14 state that adenosine binds to receptors.
D. Lines 46–50 state that theophylline binds to receptors.
E. Correct. The passage includes no evidence that phosphodiesterase binds to receptors.

The correct answer is E.

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

Spoiler: :: OA
B

Spoiler: :: OE
75. A. Phosphodiesterase is discussed in an entirely diff erent context in lines 22–25.
B. Correct. Lines 17–19 suggest that caffeine’s structural similarity to adenosine may be responsible for its ability to bind to A1 and A2 receptors.
C. Caff eine acts on neurotransmitters; it is not structurally similar to them.
D. Caffeine’s ability to stimulate behavior results from, rather than causes, this process.
E. The passage does not discuss the natural occurrence of these compounds.

The correct answer is B.

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

Spoiler: :: OA
B

Spoiler: :: OE
76. A. The quotation explains 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.

Which of the following, if true, would most weaken the theory proposed by Snyder et al?

(A) At very low concentrations in the human brain, both caffeine and theophylline tend to have depressive rather than stimulatory effects on human behavior.

(B) The ability of caffeine derivatives at very low concentrations to dislodge adenosine from its receptors in mouse brains correlates well with their ability to stimulate mouse locomotion at these low concentrations.

(C) The concentration of cyclic AMP in target neurons in the human brain that leads to increased neuron firing can be produced by several different phosphodiesterase inhibitors in addition to caffeine.

(D) The concentration of caffeine required to dislodge adenosine from its receptors in the human brain is much greater than the concentration that produces behavioral stimulation in humans.

(E) The concentration of IBMX required to dislodge adenosine from its receptors in mouse brains is much smaller than the concentration that stimulates locomotion in the mouse.

Spoiler: :: OA
D

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

Spoiler: :: OA
D

The last paragraph of the passage performs which of the following functions?

(A) Describes a disconfirming experimental result and reports the explanation given by Snyder et al in an attempt to reconcile this result with their theory.

(B) Specifies the basis for the correlation observed by Snyder et al and presents an explanation in an attempt to make the correlation consistent with the operation of psychoactive drugs other than caffeine.

(C) Elaborates the description of the correlation observed by Snyder et al and suggests an additional explanation in an attempt to make the correlation consistent with the older theory.

(D) Reports inconsistent experimental data and describes the method Snyder et al will use to reanalyze this data.

(E) Provides an example of the hypothesis proposed by Snyder et al and relates this example to caffeine’s properties.

Spoiler: :: OA
A

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.
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Re: Caffeine, the stimulant in coffee, has been called “the most widely us  [#permalink]

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20 Apr 2019, 05:44
Thanks surat
Took 21min 15sec to complete but all efforts in vain because i got only 2(3&6) right.
1. POE helped to get down to B & D but somehow i marked B. I knew the passage was discussing about two theories and in that thick of moment marked wrong one.
2. Lost somewhere between C,D & E. I have to admit that i couldn't comprehend the passage well.
3. POE to A & D. Marked A as clearly mentioned in last para.
4. Again got down to D & E and marked D only to found while reviewing that it is correct(last line of second last para).
5. Marked D with lot of confusion with B & C(Though while marking answer to Q6 realized that it was B instead but didn't correct since GMAT doesn't allow so)
6. POE to B & D where latter is trap i think.
7. At this point of time in during answering i totally lost my way and could not understand what to mark. It was simply beyond my ridiculous understanding of the passage, thus guessed B.
8. I was sure that II is true. Also i think that this is related(may be i am wrong) to Q7 in some way. But i guessed B and got it wrong.
9. Down to two i.e. A and C (eliminating D & E outright and then B). I chose C based on language of the two, thought 'disconfirming' was way too strong.

Now its been 25+ QOTDs and i am yet to see any improvement in my RCs. Generally consistent with 5-6 right(not good on any parameter) in similar passages with 8-9 Qs but getting only two right has belittled my preparation.

Have completed OG 13th edition verbal section. There also i am about 4/7 right whether timed or without timed approach.
Somehow i think my comprehension is the weakest of all links. How to improve it...??
_________________
Ephemeral Epiphany..!

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Re: Caffeine, the stimulant in coffee, has been called “the most widely us   [#permalink] 20 Apr 2019, 05:44
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