Find all School-related info fast with the new School-Specific MBA Forum

It is currently 18 Sep 2014, 10:28

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Caffeine, the stimulant in coffee, has been called “the most

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
User avatar
Joined: 09 Jun 2003
Posts: 188
Location: work chair
Followers: 2

Kudos [?]: 7 [0], given: 0

Caffeine, the stimulant in coffee, has been called “the most [#permalink] New post 17 Feb 2004, 04:10
1
This post was
BOOKMARKED
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 ceptors, 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.



71. 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

OA&OE
[Reveal] Spoiler:
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.


72. 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 fi ring and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing

OA&OE
[Reveal] Spoiler:
72. A The passage does not suggest that adenosine stimulates behavior.
B While the fi nal paragraph reveals that caff eine displays mixed eff ects, the passage does not state that adenosine has a stimulatory eff ect.
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.


73. 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

OA&OE
[Reveal] Spoiler:
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.


74. 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

OA&OE
[Reveal] Spoiler:
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. Th e passage includes no evidence that phosphodiesterase binds to receptors.

The correct answer is E.


75. 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

OA&OE
[Reveal] Spoiler:
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.



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

(A) reveal some of the assumptions underlying their theory
(B) summarize a major fi nding 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

OA&OE
[Reveal] Spoiler:
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.


Last edited by Bunuel on 15 Oct 2013, 03:23, edited 1 time in total.
Edited the question.
CEO
CEO
avatar
Joined: 15 Aug 2003
Posts: 3470
Followers: 60

Kudos [?]: 670 [0], given: 781

Caffeine, the stimulant in coffee, has been called the most [#permalink] New post 01 May 2004, 16:21
Caffeine, the stimulant in coffee, has been called "the most widely used psychoactive substance on Earth ."
Synder, Daly and Bruns have recently proposed that
caffeine affects behavior by countering the activity in
(5) 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.
(10) 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 struc-
(15) turally 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 attri-
(20) buted to its inhibition of the production of phosphodi-
esterase, an enzyme that breaks down the chemical
called cyclic AMP.A number of neurotransmitters exert
their effects by first increasing cyclic AMP concentra-
tions in target neurons. Therefore, prolonged periods at
(25) the elevated concentrations, as might be brought about
by a phosphodiesterase inhibitor, could lead to a greater
amount of neuron firing and, consequently, to behav-
ioral stimulation. But Snyder et al point out that the
caffeine concentrations needed to inhibit the production
(30) of phosphodiesterase in the brain are much higher than
those that produce stimulation. Moreover, other com-
pounds that block phosphodiesterase's activity are not
stimulants.
To buttress their case that caffeine acts instead by pre-
(35) venting 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
(40) 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 locomo-
tion." Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
(45) 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-isobuty1-1-methylxanthine(IBMX), which bound very
(50) 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
(55) 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

2. 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
phosphodi esterase 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.

3. 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) Ⅰand Ⅲ only
(D) Ⅱ and Ⅲ only
(E) Ⅰ,Ⅱ,and Ⅲ

4. 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

5. The author quotes Snyder et al in lines 38-43 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

6. 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.
Intern
Intern
avatar
Joined: 21 Mar 2004
Posts: 11
Location: Evansville, IN
Followers: 0

Kudos [?]: 0 [0], given: 0

Caffeine RC [#permalink] New post 03 May 2004, 10:53
Time: 9 minutes.
1:D
2:D
3:choices are not clear, however statement 2 and 3 are correct.
4:B
5:B
6:A

This is the toughest RC I have ever seen.
please post OA.
thanks
_________________

Best wishes
Chetan

Senior Manager
Senior Manager
User avatar
Joined: 06 Dec 2003
Posts: 366
Location: India
Followers: 1

Kudos [?]: 3 [0], given: 0

GMAT Tests User
 [#permalink] New post 04 May 2004, 02:27
Well, timing : 14 minutes

(1) D
(2) D
(3) D
(4) B
(5) E
(6) D

Dharmin
Manager
Manager
avatar
Joined: 30 May 2007
Posts: 56
Followers: 1

Kudos [?]: 4 [0], given: 0

Caffeine, the stimulant in coffee, has been called �the [#permalink] New post 30 Jul 2007, 15:46
This passage is discussed at the below mentioned link
caffeine-the-stimulant-in-coffee-has-been-called-the-128455.html#p1052696


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 affect 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 suggests 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
2. 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.
3. According so 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
4. 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
5. 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
6. 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
7. 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
8. The author quotes Snyder et al in lines 38-43 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
9. 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.
1 KUDOS received
Manager
Manager
avatar
Joined: 08 Jul 2009
Posts: 177
Followers: 3

Kudos [?]: 22 [1] , given: 13

Caffeine, the stimulant in coffee, has been called [#permalink] New post 06 Aug 2009, 11:32
1
This post received
KUDOS
Discussed in detail at the below mentioned link
caffeine-the-stimulant-in-coffee-has-been-called-the-128455.html

Caffeine, the stimulant in coffee, has been called
"the most widely used psychoactive substance on Earth ."
Synder, Daly and Bruns have recently proposed that
caffeine affects behavior by countering the activity in
(5) 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.
(10) 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 struc-
(15) turally 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 attri-
(20) buted to its inhibition of the production of phosphodi-
esterase, an enzyme that breaks down the chemical
called cyclic AMP.A number of neurotransmitters exert
their effects by first increasing cyclic AMP concentra-
tions in target neurons. Therefore, prolonged periods at
(25) the elevated concentrations, as might be brought about
by a phosphodiesterase inhibitor, could lead to a greater
amount of neuron firing and, consequently, to behav-
ioral stimulation. But Snyder et al point out that the
caffeine concentrations needed to inhibit the production
(30) of phosphodiesterase in the brain are much higher than
those that produce stimulation. Moreover, other com-
pounds that block phosphodiesterase's activity are not
stimulants.
To buttress their case that caffeine acts instead by pre-
(35) venting 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
(40) 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 locomo-
tion." Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
(45) 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-isobuty1-1-methylxanthine(IBMX), which bound very
(50) 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
(55) 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

2. 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
phosphodi esterase 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.

3. According so 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

4. 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

5. 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) Ⅰand Ⅲ only
(D) Ⅱ and Ⅲ only
(E) Ⅰ,Ⅱ,and Ⅲ

6. 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

7. 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

8. The author quotes Snyder et al in lines 38-43 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
9. 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.

[Reveal] Spoiler:
1D
2D
3D
4A
5D
6E
7B
8B
9A
Intern
Intern
avatar
Joined: 10 Jul 2009
Posts: 48
Followers: 1

Kudos [?]: 7 [0], given: 4

Re: Very Tough [#permalink] New post 06 Aug 2009, 22:39
it was quite challenging. it took me 19 min to do it.
My asnwers are
1 D
2 B - Pure CR question, tough
3 D
4 A
5 D
6 E
7 B
8 B
9 B

7/9 - not satisfying, considering that it took so much time.
Intern
Intern
avatar
Joined: 24 Sep 2008
Posts: 20
Followers: 0

Kudos [?]: 5 [0], given: 1

Re: Very Tough [#permalink] New post 07 Aug 2009, 07:48
can someone explain Q 2, Q3?

Also Q7 OA is B but chose C,
because passage says
"Snyder et al propose that caffeine, which is struc-
(15) turally similar to adenosine, is able to bind to both types
of receptors"

can someone explain why C is incorrect.

Its tough one... i took 21 min to solve all 9 and got 6/9 :cry: .

-STL
Intern
Intern
avatar
Joined: 10 Jul 2009
Posts: 48
Followers: 1

Kudos [?]: 7 [0], given: 4

Re: Very Tough [#permalink] New post 07 Aug 2009, 08:05
lalmanistl wrote:
can someone explain Q 2, Q3?

Also Q7 OA is B but chose C,
because passage says
"Snyder et al propose that caffeine, which is struc-
(15) turally similar to adenosine, is able to bind to both types
of receptors"

can someone explain why C is incorrect.

Its tough one... i took 21 min to solve all 9 and got 6/9 :cry: .

-STL

Regarding Q7 you are quoting the right sentence from the passage just and B exactly shows the right answer highliting the structural relationship between caffeine and adenosine and their ability to bind with A1 and A2 receptors.

7. 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
Manager
Manager
avatar
Joined: 08 Jul 2009
Posts: 177
Followers: 3

Kudos [?]: 22 [0], given: 13

Re: Very Tough [#permalink] New post 07 Aug 2009, 11:59
lalmanistl wrote:
can someone explain Q 2, Q3?

Also Q7 OA is B but chose C,
because passage says
"Snyder et al propose that caffeine, which is struc-
(15) turally similar to adenosine, is able to bind to both types
of receptors"

can someone explain why C is incorrect.

Its tough one... i took 21 min to solve all 9 and got 6/9 :cry: .

-STL



Question 3
The first paragraph has the clue to this. It states basically that caffeine works by attaching to receptors to which Adeonosine would have bound. They work in opposite ways, one inhibits the "firing", so the other one must at the least not be inhibiting.

Question 2
The clues are in the final paragraph where the author talks about how IBMX.
Senior Manager
Senior Manager
avatar
Joined: 25 Jul 2009
Posts: 331
Followers: 1

Kudos [?]: 26 [0], given: 0

GMAT Tests User
Re: Very Tough [#permalink] New post 07 Aug 2009, 12:13
It took me 16:31 sec and I'm more anxious about the fact is that the first four took almost 12 minutes
My answer:
1. e ---- Wrong
2. d
3. d
4. a
5. d
6. e
7. b
8. b
9. b ---- Wrong

Let me try to explain Q:2
Quote:
But Snyder et al point out that the
caffeine concentrations needed to inhibit the production
(30) of phosphodiesterase in the brain are much higher than
those that produce stimulation. Moreover, other com-
pounds that block phosphodiesterase's activity are not
stimulants.
---> if the D is true the above weaken
Again I reached by POE

Q:3 is quite straight forward

About 1, can someone confirm why its not E?
Manager
Manager
avatar
Joined: 14 Dec 2008
Posts: 171
Followers: 1

Kudos [?]: 14 [0], given: 39

GMAT Tests User
Caffeine, the stimulant in coffee, has been called "the [#permalink] New post 29 Sep 2009, 03:14
Discussed in detail at the below mentioned link
caffeine-the-stimulant-in-coffee-has-been-called-the-128455.html


Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth .”
Synder, Daly and Bruns have recently proposed that caffeine affects behavior by countering the activity in
(5)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.
(10)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 struc-
(15)turally 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 attri-
(20)buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemical called cyclic AMP.A number of neurotransmitters exert their effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at
(25)the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that the caffeine concentrations needed to inhibit the production
(30)of phosphodiesterase in the brain are much higher than those that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are not stimulants.
To buttress their case that caffeine acts instead by pre-
(35)venting 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 208
(40)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 locomo-tion.” Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most
(45) 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-isobuty1-1-methylxanthine(IBMX), which bound very
(50)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
(55)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

2. According so 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. 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. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT
(A)IBMX
(B)caffeine209
(C)adenosine
(D)theophylline
(E)phosphodiesterase

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. The author quotes Snyder et al in lines 38-43 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
Intern
Intern
avatar
Joined: 20 May 2010
Posts: 25
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: RC - Caffeine [#permalink] New post 20 May 2010, 17:33
I has B D A E B B , read only question and just find only specific answer in article ( but it took me more than 20 min!! need to practice this technic more)
Intern
Intern
avatar
Joined: 17 Jan 2011
Posts: 6
Followers: 0

Kudos [?]: 0 [0], given: 0

Re: Very Tough [#permalink] New post 06 Jul 2011, 10:50
stumbled upon this while studying
D, D, D, A, D, E, B, B, A
Took 17 minutes, but i think I got it all right.

This is by far the hardest RC passage I've come across in my studies.. I don't think that's a good thing =(
Senior Manager
Senior Manager
avatar
Joined: 10 Nov 2010
Posts: 268
Location: India
Concentration: Strategy, Operations
GMAT 1: 520 Q42 V19
GMAT 2: 540 Q44 V21
WE: Information Technology (Computer Software)
Followers: 5

Kudos [?]: 49 [0], given: 22

GMAT Tests User
Caffeine, the stimulant in coffee, has been called "the [#permalink] New post 02 Mar 2012, 03:04
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 affect 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 suggests 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
[Reveal] Spoiler:
D


2. According so 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
[Reveal] Spoiler:
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
[Reveal] Spoiler:
A


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
[Reveal] Spoiler:
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
[Reveal] Spoiler:
B


6. The author quotes Snyder et al in lines 38-43 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
[Reveal] Spoiler:
B


7. 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.
I only
I and II only
I and III only
I, II, and III
II and III only
[Reveal] Spoiler:
D


8. 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.
[Reveal] Spoiler:
B


9. 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.


[Reveal] Spoiler:
A


I marked C for Q7

But OA is different.
Pls confirm OA or my mistake
_________________

The proof of understanding is the ability to explain it.

Senior Manager
Senior Manager
avatar
Joined: 18 Sep 2009
Posts: 373
Followers: 3

Kudos [?]: 74 [0], given: 2

GMAT Tests User
Caffeine, the stimulant in coffee, has been called the most [#permalink] New post 03 Apr 2012, 08:20
Discussed in detail at the below mentioned link
caffeine-the-stimulant-in-coffee-has-been-called-the-128455.html

Caffeine, the stimulant in coffee, has been called
“the most widely used psychoactive substance on Earth .”
Synder, 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 struc-
turally 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 attri-
buted 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 caffeineacts instead by pre-
venting 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-isobuty1-1-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.

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.
I eliminated options a,b,c but unable to decide between D and E. please explain
[Reveal] Spoiler:
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
" least partially attiributed" means?
[Reveal] Spoiler:
b
Manager
Manager
avatar
Status: Bunuel's fan!
Joined: 08 Jul 2011
Posts: 238
Followers: 0

Kudos [?]: 17 [0], given: 55

Re: RC [#permalink] New post 06 May 2012, 01:57
4. (E) phosphodiesterase because
Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
effective compounds in both regards. Hence eliminate D


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?
(B) The structural relationship between caffeine and adenosine
" least partially attiributed" means? That mean can be at least because of, due to. The paragraph mentioned:
Snyder et al propose that caffeine, which is struc-
turally 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.
Expert Post
Retired Moderator
avatar
Status: worked for Kaplan's associates, but now on my own, free and flying
Joined: 19 Feb 2007
Posts: 2266
Location: India
WE: Education (Education)
Followers: 263

Kudos [?]: 1601 [0], given: 249

Caffeine, the stimulant in coffee, has been called [#permalink] New post 12 Oct 2013, 21:10
Expert's post
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 ceptors, 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.



71. 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

OA&OE
[Reveal] Spoiler:
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.


72. 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 fi ring and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing

OA&OE
[Reveal] Spoiler:
72. A The passage does not suggest that adenosine stimulates behavior.
B While the fi nal paragraph reveals that caff eine displays mixed eff ects, the passage does not state that adenosine has a stimulatory eff ect.
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.


73. 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

OA&OE
[Reveal] Spoiler:
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.


74. 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

OA&OE
[Reveal] Spoiler:
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. Th e passage includes no evidence that phosphodiesterase binds to receptors.

The correct answer is E.


75. 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

OA&OE
[Reveal] Spoiler:
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.



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

(A) reveal some of the assumptions underlying their theory
(B) summarize a major fi nding 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

OA&OE
[Reveal] Spoiler:
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.


_________________

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Intern
Intern
avatar
Joined: 01 Feb 2013
Posts: 13
Followers: 0

Kudos [?]: 1 [0], given: 14

Re: Caffeine, the stimulant in coffee, has been called “the most [#permalink] New post 12 Sep 2014, 21:17
For Q2 of the second version of questions, I find 2 options suitable. No idea which is correct

2. 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 - Last Paragraph says that it doesn't correlate at very low concentrations but infact produces the opposite result.

(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 phosphodi esterase 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. - This altogether breaks down the hypothesis as behavioral responses are induced much before adenosine is dislodged which might be due to some other reason.

(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.
Re: Caffeine, the stimulant in coffee, has been called “the most   [#permalink] 12 Sep 2014, 21:17
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic Caffeine, the stimulant in coffee, has been called daagh 0 12 Oct 2013, 21:10
Caffeine, the stimulant in coffee, has been called the most TomB 0 06 May 2012, 01:57
Caffeine, the stimulant in coffee, has been called "the manojgmat 0 01 Jun 2010, 06:34
Caffeine, the stimulant in coffee, has been called sher676 0 15 Jan 2012, 03:36
Caffeine, the stimulant in coffee, has been called �the nehanishika 0 30 Jul 2007, 15:46
Display posts from previous: Sort by

Caffeine, the stimulant in coffee, has been called “the most

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.