How does the brain know when carbohydrates have been or shou : GMAT Reading Comprehension (RC)
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# How does the brain know when carbohydrates have been or shou

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How does the brain know when carbohydrates have been or shou [#permalink]

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05 Mar 2009, 09:41
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How does the brain know when carbohydrates have been or should be consumed? The answer to this question is not known, but one element in the explanation seems to be the neurotransmitter serotonin, one of a class of chemical mediators that may be released from a presynaptic neuron and that cause the transmission of a nerve impulse across a synapse to an adjacent postsynaptic neuron. In general, it has been found that drugs that selectively facilitate serotonin-mediated neurotransmission tend to cause weight loss, whereas drugs that block serotonin-mediated transmission often have the opposite effect: they often induce carbohydrate craving and consequent weight gain.
Serotonin is a derivative of tryptophan, an amino acid that is normally present at low levels in the bloodstream. The rate of conversion is affected by the proportion of carbohydrates in an individual’s diet: carbohydrates stimulate the secretion of insulin, which facilitates the uptake of most amino acids into peripheral tissues, such as muscles. Blood tryptophan levels, however, are unaffected by insulin, so the proportion of tryptophan in the blood relative to the other amino acids increases when carbohydrates are consumed. Since tryptophan competes with other amino acids for transport across the blood-brain barrier into the brain, insulin secretion indirectly speeds tryptophan’s entry into the central nervous system where, in a special cluster of neurons, it is converted into serotonin.

The level of serotonin in the brain in turn affects the amount of carbohydrate an individual chooses to eat. Rats that are allowed to choose among synthetic foods containing different proportions of carbohydrate and protein will normally alternate between foods containing mostly protein and those containing mostly carbohydrate. However, if rats are given drugs that enhance the effect of serotonin, the rats’ carbohydrate intake is reduced. On the other hand, when rats are given drugs that interrupt serotonin-mediated neurotransmission, their brains fail to respond when carbohydrates are eaten, so the desire for them persists.

In human beings a serotoninlike drug, d-fenfluramine (which release serotonin into brain synapses and then prolong its action by blocking its reabsorption into the presynaptic neuron), selectively suppresses carbohydrate snacking (and its associated weight gain) in people who crave carbohydrates. In contrast, drugs that block serotonin-mediated transmission or that interact with neurotransmitters other than serotonin have the opposite effect: they often induce carbohydrate craving and subsequent weight gain. People who crave carbohydrates report feeling refreshed and invigorated after eating a carbohydrate-rich meal (which would be expected to increase brain serotonin levels), in contrast, those who do not crave carbohydrates become sleepy following a high-carbohydrate meal. These findings suggest that serotonin has other effects that may be useful indicators of serotonin levels in human beings.
21. Which one of the following best states the main idea of the passage
(A) The body’s need for carbohydrates varies with the level of serotonin in the blood.
(B) The body’s use of carbohydrates can be regulated by the administration of serotoninlike drugs.
(C) The role of serotonin in regulating the consumption of carbohydrates is similar in rats and in humans.
(D) The body’s desire for carbohydrates can be influenced by serotonin or serotoninlike drugs.
(E) Tryptophan initiates a chain of events that regulates the body’s use of carbohydrates.

[Reveal] Spoiler:
D

22. The term “rate” (line 17) refers to the rate at which
(A) serotonin is produced from tryptophan
(B) carbohydrates are taken into the body
(C) carbohydrates stimulate the secretion of insulin
(D) insulin facilitates the uptake of amino acids into peripheral tissues
(E) tryptophan enters the bloodstream

[Reveal] Spoiler:
A

23. It can be inferred that a person is likely to CRAVE carbohydrates when
(A) the amount of insulin produced is too high
(B) the amount of serotonin in the brain is too low
(C) more tryptophan than usual crosses the blood-brain barrier
(D) neurotransmission by neurotransmitters other than serotonin is interrupted
(E) amino acids other than tryptophan are taken up by peripheral tissues

[Reveal] Spoiler:
B

24. The information in the passage indicates that if human beings were given a drug that inhibits the action of serotonin, which one of the following might be expected to occur?
(A) Subjects would probably show a preference for carbohydrate-rich snacks rather than protein-rich snacks.
(B) Subjects would probably become sleepy after eating a carbohydrate-rich meal.
(C) Subjects would be more likely to lose weight than before they took the drug.
(D) Subjects’ blood tryptophan levels would probably increase.
(E) Subjects’ desire for both carbohydrates and proteins would increase.

[Reveal] Spoiler:
A

25. The primary purpose of the second paragraph in the passage is to
(A) provide an overview of current research concerning the effect of serotonin on carbohydrate consumption
(B) contrast the role of tryptophan in the body with that of serotonin
(C) discuss the role of serotonin in the transmission of neural impulses
(D) explain how the brain knows that carbohydrates should be consumed
(E) establish a connection between carbohydrate intake and the production of serotonin

[Reveal] Spoiler:
E

26. It can be inferred that after a person has taken d-fenflurarmine, he or she will probably be
(A) inclined to gain weight
(B) sleepy much of the time
(C) unlikely to crave carbohydrates
(D) unable to sleep as much as usual
(E) likely to secrete more insulin than usual

[Reveal] Spoiler:
C

27. The author’s primary purpose is to
(A) defend a point of view
(B) correct a misconception
(C) assess conflicting evidence
(D) suggest new directions for investigation
(E) provide information that helps explain a phenomenon

[Reveal] Spoiler:
E

Hope you guys enjoying the type of passages I am posting so far
pls suggest so that we can improve further
once I get 3-4 responses, i will post the OAs(if needed OEs also)
thanks

edited Q No 23
its CRAVE and not CARVE as typed earlier
[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA
[Reveal] Spoiler: Question #5 OA
[Reveal] Spoiler: Question #6 OA
[Reveal] Spoiler: Question #7 OA

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Last edited by fameatop on 04 Aug 2013, 07:30, edited 3 times in total.
OA not Provided & improper formatting
If you have any questions
New!
VP
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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05 Mar 2009, 15:12
1
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Got D,A,B,A,E,C,E

Found the first Q awfully tough. Ended up taking 4 min for that single Q and took 18 on a whole. Jeez! I should learn to let go..

Desire vs need??

role of serotonin levels vs serotonin like drugs.

Chose A flipped to D,flipped back to A and then back to D

That Q is nasty. The final line suggests that the answer probably is A

The first para suggests that the answer probably is D.

OE for the first one please?

Chose A for Q 24 very uncomfortably as I needed to bring the results from Rats experiment.

Thanks
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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05 Mar 2009, 23:47
1
KUDOS
Nitya, I must appreciate that u r posting passages of all types. This is very imp. Keep it up.
I alw find medical passages difficult. Relating all phenomenon with each other is alw a daunting task 4 me. So naturally this passage was difficult 2 me.anyways, here r my answers:
21 D
22 A
23 B
24 B
25 E
26 C
27 E

Waiting for OAs
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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05 Mar 2009, 09:58
21. D
22. A
23. B
24. B
25. E
26. C
27. E

I am not posting explanations. In case we need to discuss a question, we can start posting explanations too.
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 07:34
Ritula and Sc thakur please Explain q .24
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rampuria

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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 07:59
21. D
22. A
23. B
24. B
25. E
26. C
27. E
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 08:21
Let us know the OA first.
rampuria wrote:
Ritula and Sc thakur please Explain q .24
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 08:50
Thanks Friends!!
Its among the Worst of passages!!Atleast we can conclude that.
Passage was not that tough but Qs (and the choices )were tricky

I tried this way
Serotonin-->UP; Weight-->DOWN like that ..to build up a mental map(invisible "short notes" you can say)
My try
21-D
22-E
23-A
24-tricky
for rats, its defined...carbo+Protein etc
B?
25-E
26-C
27-E
I will post the OAs and few OEs in no time
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Kudos [?]: 576 [0], given: 17

Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 09:03
Awesome
Those were OAs
yes
DABAECE
icandy wrote:
Got D,A,B,A,E,C,E

Found the first Q awfully tough. Ended up taking 4 min for that single Q and took 18 on a whole. Jeez! I should learn to let go..

Desire vs need??

role of serotonin levels vs serotonin like drugs.

Chose A flipped to D,flipped back to A and then back to D

That Q is nasty. The final line suggests that the answer probably is A

The first para suggests that the answer probably is D.

OE for the first one please?

Chose A for Q 24 very uncomfortably as I needed to bring the results from Rats experiment.

Thanks

_________________

http://gmatclub.com/forum/math-polygons-87336.html
http://gmatclub.com/forum/competition-for-the-best-gmat-error-log-template-86232.html

Senior Manager
Joined: 04 Sep 2008
Posts: 259
Location: Kolkata
Schools: La Martiniere for Boys
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 09:17
nitya34 wrote:
Awesome
Those were OAs
yes
DABAECE
icandy wrote:
Got D,A,B,A,E,C,E

Found the first Q awfully tough. Ended up taking 4 min for that single Q and took 18 on a whole. Jeez! I should learn to let go..

Desire vs need??

role of serotonin levels vs serotonin like drugs.

Chose A flipped to D,flipped back to A and then back to D

That Q is nasty. The final line suggests that the answer probably is A

The first para suggests that the answer probably is D.

OE for the first one please?

Chose A for Q 24 very uncomfortably as I needed to bring the results from Rats experiment.

Thanks

_________________

Thanks
rampuria

Director
Joined: 04 Jan 2008
Posts: 912
Followers: 69

Kudos [?]: 576 [0], given: 17

Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 09:44
24. (A)
Serotonin reduces the body’s desire for carbohydrates, so test
subjects given a drug that inhibits serotonin’s function would naturally tend to crave foods
that are rich in carbohydrates, rather than foods that are rich in substances like protein.
(B) People who crave carbohydrates would feel refreshed after eating a carbohydrate-filled
meal. People who don’t crave carbohydrates, in contrast, would feel sleepy.
(C) Wrong again. As lines 13-14 and 54-55 indicate, desire for carbohydrates and weight
gain go hand-in-hand.
(D) Wrong again. If the amount of serotonin produced by the body is inhibited by a drug,
then blood tryptophan levels, which determine serotonin levels, would also likely decrease
as a consequence of the drug’s affects.
(E) Wrong!The increased desire for carbohydrate-rich foods comes at the
expense of foods that are rich in substances like protein.
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 20:19
Nithya thanks for doing this. I got 4/7 and took forever
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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06 Mar 2009, 22:47
yup it was a tough one. though im glad dat i got only one wrong.
nitya34 wrote:
24. (A)
Serotonin reduces the body’s desire for carbohydrates, so test
subjects given a drug that inhibits serotonin’s function would naturally tend to crave foods
that are rich in carbohydrates, rather than foods that are rich in substances like protein.
(B) People who crave carbohydrates would feel refreshed after eating a carbohydrate-filled
meal. People who don’t crave carbohydrates, in contrast, would feel sleepy.
(C) Wrong again. As lines 13-14 and 54-55 indicate, desire for carbohydrates and weight
gain go hand-in-hand.
(D) Wrong again. If the amount of serotonin produced by the body is inhibited by a drug,
then blood tryptophan levels, which determine serotonin levels, would also likely decrease
as a consequence of the drug’s affects.
(E) Wrong!The increased desire for carbohydrate-rich foods comes at the
expense of foods that are rich in substances like protein.
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Re: RC No 3-Carbohydrates and Serotonin-6th March [#permalink]

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04 Aug 2013, 05:10
DABDECE...OA timing-IR4:27..total:17mins
Re: RC No 3-Carbohydrates and Serotonin-6th March   [#permalink] 04 Aug 2013, 05:10
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