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It was once believed that the brain was independent of meta

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It was once believed that the brain was independent of meta  [#permalink]

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New post Updated on: 18 Nov 2017, 05:21
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It was once believed that the brain was
independent of metabolic processes occurring
elsewhere in the body. In recent studies, however,
we have discovered that the production and release
(5) in brain neurons of the neurotransmitter serotonin
(neurotransmitters are compounds that neurons use
to transmit signals to other cells) depend directly on
the food that the body processes.

Our first studies sought to determine whether
(10) the increase in serotonin observed in rats given
a large injection of the amino acid tryptophan
might also occur after rats ate meals that change
tryptophan levels in the blood. We found that,
immediately after the rats began to eat, parallel
(15) elevations occurred in blood tryptophan, brain
tryptophan, and brain serotonin levels. These
findings suggested that the production and release
of serotonin in brain neurons were normally coupled
with biood-tryptophan increases. In later studies we
(20) found that injecting insulin into a rat's bloodstream
also caused parallel elevations in blood and brain
tryptophan levels and in serotonin levels. We then
decided to see whether the secretion of the animal's
own insulin similarly affected serotonin production.
(25) We gave the rats a carbohydrate-containing meal
that we knew would elicit insulin secretion. As we
had hypothesized, the blood tryptophan level and
the concentrations of tryptophan and of serotonin
in the brain increased after the meal.

(30) Surprisingly, however, when we added a large
amount of protein to the meal, brain tryptophan
and serotonin levels fell. Since protein contains
tryptophan, whyshould it depress brain tryptophan
levels? The answer lies in the mechanism that
(35) provides blood tryptophan to the brain cells. This
same mechanism also provides the brain cells with
other amino acids found in protein, such as tyrosine
and leucine. The consumption of protein increases
blood concentration of the other amino acids much
(40) more, proportionately, than it does that of tryptophan.
The more protein is in a meal, the lower is the ratio
of the resulting blood-tryptophanconcentration to
the concentration of competing amino acids, and
the more slowly is tryptophan provided to the brain.
(45) Thus the more protein in a meal, the less serotonin
subsequently produced and released.

Which of the following titles best summarizes the contents of the passage?

(A) Neurotransmitters: Their Crucial Function in Cellular Communication
(B) Diet and Survival: An Old Relationship Reexamined
(C) The Blood Supply and the Brain: A Reciprocal Dependence
(D) Amino Acids and Neurotransmitters: The Connection between Serotonin Levels and Tyrosine
(E) The Effects of Food Intake on the Production and Release of Serotonin: Some Recent Findings



According to the passage, the speed with which tryptophan is provided to the brain cells of a rat varies with the

(A) amount of protein present in a meal
(B) concentration of serotonin in the brain before a meal
(C) concentration of leucine in the blood rather than with the concentration of tyrosine in the blood after a meal
(D) concentration of tryptophan in the brain before a meal
(E) number of serotonin-containing neurons



According to the passage, when the authors began their first studies, they were aware that

(A) they would eventually need to design experiments that involved feeding rats high concentrations of protein
(B) tryptophan levels in the blood were difficult to monitor with accuracy
(C) serotonin levels increased after rats were fed meals rich in tryptophan
(D) there were many neurotransmitters whose production was dependent on metabolic processes elsewhere in the body
(E) serotonin levels increased after rats were injected with a large amount oftryptophan



According to the passage, one reason that the authors gave rats carbohydrates was to

(A) depress the rats' tryptophan levels
(B) prevent the rats from contracting diseases
(C) cause the rats to produce insulin
(D) demonstrate that insulin is the most important substance secreted by the body
(E) compare the effect of carbohydrates with the effect of proteins



Accordingto the passage, the more protein a rat consumes, the lower will be the

(A) ratio of the rat's blood-tryptophan concentration to the amount of serotonin produced and released in the rat's brain
(B) ratioof the rat's blood-tryptophan concentration to the concentration in its blood of the other amino acids contained in the protein
(C) ratio of the rat's blood-tyrosine concentration to its blood-leucine concentration
(D) number of neurotransmitters of any kindthat the rat will produce and release
(E) number of amino acids the rat's blood will contain



The authors' discussion of the "mechanism that provides blood tryptophan to the brain cells" (lines 34-35) is meant to

(A) stimulate further research studies
(B) summarize an area of scientific investigation
(C) help explain why a particular research finding was obtained
(D) provide supporting evidence for a controversial scientific theory
(E) refutethe conclusions of a previously mentioned research study



According to the passage, an injection of insulin was most similar in its effect on rats to an injection of

(A) tyrosine
(B) leucine
(C) blood
(D) tryptophan
(E) protein



It can be inferred from the passage that which of the following would be LEAST likelyto be a potential source of aid to a patient who was not adequately producing and releasing serotonin?

(A) Meals consisting almost exclusively of protein
(B) Meals consisting almost exclusively of carbohydrates
(C) Meals that would elicit insulin secretion
(D) Meals that had very low concentrations of tyrosine
(E) Meals that had very low concentrations of leucine



Itcan be inferred from the passage that the authors initially held which of the following hypotheses about what would happen when they fed large amounts of protein to rats?

(A) The rats' brain serotonin levels would not decrease.
(B) The rats' brain tryptophan levels would decrease.
(C) The rats' tyrosine levels would increase less quickly than would their leucine levels.
(D) The rats would produce more insulin.
(E) The rats would produce neurotransmitters other than serotonin.



Try this under time condition. Good luck
As usual are glad answers and explanations
rgards

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Originally posted by carcass on 23 Aug 2013, 13:10.
Last edited by broall on 18 Nov 2017, 05:21, edited 2 times in total.
Reformatted questions
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 23 Aug 2013, 14:21
3
carcass wrote:
It was once believed that the brain was
independent of metabolic processes occurring
elsewhere in the body. In recent studies, however,
we have discovered that the production and release
(5) in brain neurons of the neurotransmitter serotonin
(neurotransmitters are compounds that neurons use
to transmit signals to other cells) depend directly on
the food that the body processes.
Our first studies sought to determine whether
(10) the increase in serotonin observed in rats given
a large injection of the amino acid tryptophan
might also occur after rats ate meals that change
tryptophan levels in the blood. Wefound that,
immediately after the rats began to eat, parallel
(15) elevations occurred in blood tryptophan, brain
tryptophan, and brain serotonin levels. These
findings suggested that the production and release
of serotonin in brain neurons were normally coupled
with biood-tryptophan increases. In later studies we
(20) found that injecting insulin into a rat's bloodstream
also caused parallel elevations in blood and brain
tryptophan levels and in serotonin levels. We then
decided to see whether the secretion of the animal's
own insulin similarly affected serotonin production.
(25) We gave the rats a carbohydrate-containing meal
that we knew would elicit insulin secretion. As we
had hypothesized, the blood tryptophan level and
the concentrations of tryptophan and of serotonin
in the brain increased after the meal.
(30) Surprisingly, however, when we added a large
amount of protein to the meal, brain tryptophan
and serotonin levels fell. Since protein contains
tryptophan, whyshould it depress brain tryptophan
levels? The answer lies in the mechanism that
(35) provides blood tryptophan to the brain cells. This
same mechanism also provides the brain cells with
other amino acids found in protein, such as tyrosine
and leucine. The consumption of protein increases
blood concentration of the other amino acids much
(40) more, proportionately, than it does that of tryptophan.
The more protein is in a meal, the lower is the ratio
of the resulting blood-tryptophanconcentration to
the concentration of competing amino acids, and
the more slowly is tryptophan provided to the brain.
(45) Thus the more protein in a meal, the less serotonin
subsequently produced and released.
Which of the following titles best summarizes the
contents of the passage?
(A) Neurotransmitters: Their Crucial Function in
Cellular Communication
(B) Diet and Survival: An Old Relationship
Reexamined
(C) The Blood Supply and the Brain: A Reciprocal
Dependence
(D) Amino Acids and Neurotransmitters: The
Connection between Serotonin Levels and
Tyrosine
(E) The Effects of Food Intake on the Production
and Release of Serotonin: Some Recent Findings


According to the passage, the speed with which
tryptophan is provided to the brain cells of a rat varies
with the
(A) amount of protein present in a meal
(B) concentration of serotonin in the brain before
a meal
(C) concentration of leucine in the blood rather than
with the concentration of tyrosine in the blood
after a meal
(D) concentration of tryptophan in the brain before
a meal
(E) number of serotonin-containing neurons


According to the passage, when the authors began
their first studies, they were aware that
(A) they would eventually need to design
experiments that involved feeding rats high
concentrations of protein
(B) tryptophan levels in the blood were difficult to
monitor with accuracy
(C) serotonin levels increased after rats were fed
meals rich in tryptophan
(D) there were many neurotransmitters whose
production was dependent on metabolic
processes elsewhere in the body
(E) serotonin levels increased after rats were
injected with a large amount oftryptophan

According to the passage, one reason that the authors
gave rats carbohydrates was to
(A) depress the rats' tryptophan levels
(B) prevent the rats from contracting diseases
(C) cause the rats to produce insulin >
(D) demonstrate that insulin is the most important
substance secreted by the body
(E) compare the effect of carbohydrates with the
effect of proteins


Accordingto the passage, the more protein a rat
consumes, the lower will be the
(A) ratio of the rat's blood-tryptophan concentration
to the amount of serotonin produced and
released in the rat's brain
(B) ratioof the rat's blood-tryptophan concentration
to the concentration in its blood of the other
amino acids contained in the protein
(C) ratio of the rat's blood-tyrosine concentration to
its blood-leucine concentration
(D) number of neurotransmitters of any kindthat the
rat will produce and release
(E) number of amino acids the rat's blood will
contain

The authors' discussion of the "mechanism that
provides blood tryptophan to the brain cells" (lines
34-35) is meant to
(A) stimulate further research studies
(B) summarize an area of scientific investigation
(0 help explain why a particular research finding
was obtained
(D) provide supporting evidence for a controversial
scientific theory
(E) refutethe conclusions of a previously mentioned
research study


According to the passage, an injection of insulin was
most similar in its effect on rats to an injection of
(A) tyrosine
(B) leucine
(C) blood
(D) tryptophan
(E) protein


It can be inferred from the passage that which of the
following would be LEAST likelyto be a potential
source of aid to a patient who was not adequately
producing and releasing serotonin?
(A) Meals consisting almost exclusively of protein
(B) Meals consisting almost exclusively of
carbohydrates
(0 Meals that would elicit insulin secretion
(D) ,Meals that had very low concentrations of
tyrosine
(E) Meals that had very low concentrations of
leucine


Itcan be inferred from the passage that the authors
initially held which of the following hypotheses about
what would happen when they fed large amounts of
protein to rats?
(A) The rats' brain serotonin levels would not
decrease.
(B) The rats' brain tryptophan levels would
decrease.
(C) The rats' tyrosine levels would increase less
quickly than would their leucine levels.
(D) The rats would produce more insulin.
(E) The rats would produce neurotransmitters other
than serotonin.



Try this under time condition. Good luck

As usual are glad answers and explanations

rgards


Here are the answers with explanations:


1. Accordingto the passage, the more protein a rat consumes, the lower will be the
Ans : (E) The Effects of Food Intake on the Production and Release of Serotonin: Some Recent Findings
Mentioned in the very first passage.

2. According to the passage, the speed with which tryptophan is provided to the brain cells of a rat varies with the
Ans : (A) amount of protein present in a meal
The variation in the speed with which tryptophan is provided to the brain cells is correlated with amount of protein present in meal in lines 30 to 32.

3. According to the passage, when the authors began their first studies, they were aware that
Ans : (E) serotonin levels increased after rats were injected with a large amount oftryptophan
From lines 10 to 14 it is clear that scientists were already aware that serotonin levels increased after rats were injected with a large amount of tryptophan and they wanted to verify if the same happens after rats eat meals that change tryptophan levels in the blood.

4. According to the passage, one reason that the authors gave rats carbohydrates was to
Ans : (C) cause the rats to produce insulin >
Clearly mentioned in lines 25-26/

5. According to the passage, the more protein a rat consumes, the lower will be the
Ans : (B) ratioof the rat's blood-tryptophan concentration to the concentration in its blood of the other amino acids contained in the protein
Mentioned in lines 38 to 40

6. The authors' discussion of the "mechanism that provides blood tryptophan to the brain cells" (lines 34-35) is meant to
Ans : (c) help explain why a particular research finding was obtained
Scientists found that when rats are fed with protein, the brain tryptophan and serotonin levels fell. In order to explain this particular finding they discussed about the mechanism which provides blood tryptophan to the brain cells.

7. According to the passage, an injection of insulin was most similar in its effect on rats to an injection of
Ans : (D) tryptophan
Lines 10 to 11 indicate that injecting amino acid tryptophan increased the serotonin level in brain. Similarly from lines 19 to 22 it is clear that injecting rats with insulin increased tryptophan which in turn increased the serotonin level.

8. It can be inferred from the passage that which of the following would be LEAST likelyto be a potential source of aid to a patient who was not adequately producing and releasing serotonin?
Ans : (A) Meals consisting almost exclusively of protein
All other options mention source of aid desired for patient who was not adequately producing and releasing serotonin.

9. Itcan be inferred from the passage that the authors initially held which of the following hypotheses about what would happen when they fed large amounts of protein to rats?
Ans : (A) The rats' brain serotonin levels would not decrease.
All the other options don't make sense. Though, as scientists had fed large amounts of protien to rats they must have expected the tryptophan level to increase. In answer options only option A comes in line with this. They must have thought that at least the tryptophan level shall not decrease.
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 19 Oct 2015, 13:17
1
Great Passage. But, is this really a 700 level question? If so, is it because it contains more questions in the passage?
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 13 Aug 2017, 02:12
chandrae wrote:
Great Passage. But, is this really a 700 level question? If so, is it because it contains more questions in the passage?


Doesn't appear to be a 700-level question.

Also, 9 questions from a single passage is a stretch. Maximum, I have seen is 6 for a longer passage.
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 15 Mar 2018, 12:21
8/9 - 11 Minutes. Not bad i believe.
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 16 Mar 2018, 06:08
All correct in 13 mins , including 4 mins 30 seconds to read . Took more time on Q3
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It was once believed that the brain was independent of meta  [#permalink]

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New post 05 Oct 2018, 22:08
P1 - a believed theory provved wrong.
P2 - proof of theory in P1.
P3 - more evidence but in reverse direction.
Main point - a theory was discarded, multiple evidences are given to prove that.

Which of the following titles best summarizes the contents of the passage?

(A) Neurotransmitters: Their Crucial Function in Cellular Communication - no
(B) Diet and Survival: An Old Relationship Reexamined - no
(C) The Blood Supply and the Brain: A Reciprocal Dependence - no
(D) Amino Acids and Neurotransmitters: The Connection between Serotonin Levels and Tyrosine - p3
(E) The Effects of Food Intake on the Production and Release of Serotonin: Some Recent Findings - to the point

--------------------------------------------
According to the passage, the speed with which tryptophan is provided to the brain cells of a rat varies with the

when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.

(A) amount of protein present in a meal
--------------------------------------------

According to the passage, when the authors began their first studies, they were aware that

Our first studies sought to determine whether (10) the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood.

(E) serotonin levels increased after rats were injected with a large amount of tryptophan

---------------------------------------------

According to the passage, one reason that the authors gave rats carbohydrates was to
lines to read - We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion.
(C) cause the rats to produce insulin
------------------------------------------------
According to the passage, the more protein a rat consumes, the lower will be the

the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. (45) Thus the more protein in a meal, the less serotonin subsequently produced and released.

(B) ratioof the rat's blood-tryptophan concentration to the concentration in its blood of the other amino acids contained in the protein

-------------------------------------------------
The authors' discussion of the "mechanism that provides blood tryptophan to the brain cells" (lines 34-35) is meant to

PT - no doubt this is explanation for the previous findings.
(C) help explain why a particular research finding was obtained -

-------------------------------------------------

According to the passage, an injection of insulin was most similar in its effect on rats to an injection of
injecting insulin into a rat's bloodstream also caused parallel elevations in blood and brain tryptophan levels

(D) tryptophan -
-------------------------------------------

It can be inferred from the passage that which of the following would be LEAST likely to be a potential source of aid to a patient who was not adequately producing and releasing serotonin?

when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.

(A) Meals consisting almost exclusively of protein - straight A

---------------------------------------------

Itcan be inferred from the passage that the authors initially held which of the following hypotheses about what would happen when they fed large amounts of protein to rats?

Thus the more protein in a meal, the less serotonin subsequently produced and released.

(A) The rats' brain serotonin levels would not decrease.
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 24 Apr 2019, 05:42
1. Which of the following titles best summarizes the contents of the passage?

(A) Neurotransmitters: Their Crucial Function in Cellular Communication
This option talks about neurotransmitters in general but in the passage we are talking about a specific kind of neurotransmitter- Serotonin.

(B) Diet and Survival: An Old Relationship Reexamined. Completely out of scope.
No where in the passage survival is talked about

(C) The Blood Supply and the Brain: A Reciprocal Dependence.
This passage is about the release of serotonin and tryptophan in brain with respect to various types of food. Hence this option is out of scope.

(D) Amino Acids and Neurotransmitters: The Connection between Serotonin Levels and Tyrosine
The Connection between Serotonin Levels and Tyrosine is used as a case in point for the main point of the passage.

(E) The Effects of Food Intake on the Production and Release of Serotonin: Some Recent Findings
Exactly the gist of the passage.

2. According to the passage, the speed with which tryptophan is provided to the brain cells of a rat varies with the

(A) amount of protein present in a meal
Quote:
The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophanconcentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain.

The above line talks about speed in the context of protein meal. Hence A is the answer.

(B) concentration of serotonin in the brain before a meal
The author says that the concentration of serotonin increases after a carbohydrate meal but nothing about its concentration before a mean and its speed.

(C) concentration of leucine in the blood rather than with the concentration of tyrosine in the blood after a meal
The author mentions leucine and tyrosine as examples of a mechansim he was explaining. Tyrosine and leucine concentration have nothing to do with the speed with which tryptophan is provided to the brain cells of a rat.
Quote:
This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine.


(D) concentration of tryptophan in the brain before a meal
Again concentration of tryptohan in the brain before a meal was never implied in the passage.

(E) number of serotonin-containing neurons
This number is never mentioned in the passage let alone in the context of speed with which tryptophan is provided to the brain cells of a rat.

3. According to the passage, when the authors began their first studies, they were aware that

Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood.
Since authors already know that with the injection of tryptophan, serotonin increases, they are hoping to finding out if the same happens in the case of food.

(A) they would eventually need to design experiments that involved feeding rats high concentrations of protein
Nothing about protein is mentioned in this part of the passage.

(B) tryptophan levels in the blood were difficult to monitor with accuracy
Nothing about difficulty of monitoring.

(C) serotonin levels increased after rats were fed meals rich in tryptophan.
Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood.
They don't already know it.They are hoping to finding out if serotonin levels increased after rats were fed meals rich in tryptophan.


(D) there were many neurotransmitters whose production was dependent on metabolic processes elsewhere in the body.
Completely out of context.

(E) serotonin levels increased after rats were injected with a large amount of tryptophan
Correct. According to the above quoted text from the passage, we can infer this.

6. The authors' discussion of the "mechanism that provides blood tryptophan to the brain cells" (lines 34-35) is meant to

Quote:
Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine.


The author says since protein contains tryptophan and when one consumes protein, the tryptophan levels should increase in the brain. But that is not the case and he questions why. In the next line, he answers his question and says that 'due to the mechanism', this happens. So, he is mentioning 'mechanism' to explain why tryptophan levels are decreasing.

(A) stimulate further research studies
Nothing about further research was mentioned in the passage.

(B) summarize an area of scientific investigation.
Authors are not summarizing.

(C) help explain why a particular research finding was obtained
Yes. correct answer.

(D) provide supporting evidence for a controversial scientific theory
Nothing controversial was mentioned in the passage.

(E) refute the conclusions of a previously mentioned research study
The authors by saying that tryptophan levels decrease in the brain when protein rich meal is consumed, are not refuting the fact that tryptophan levels increase in the brain when meals elicit insulin secretion (mentioned in the previous passage). He is merely explaining the effect of protein on tryptophan production in brain.

8. It can be inferred from the passage that which of the following would be LEAST likely to be a potential source of aid to a patient who was not adequately producing and releasing serotonin?

(A) Meals consisting almost exclusively of protein
Quote:
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.

Hence the right answer.

(B) Meals consisting almost exclusively of carbohydrates
This is likely suitable. Hence , not the answer.

(C) Meals that would elicit insulin secretion
This is most likely suitable. Hence , not the answer.

(D) Meals that had very low concentrations of tyrosine
Out of scope. We do not know the effects of tyrosine in production and release of sorotonin.

(E) Meals that had very low concentrations of leucine
Out of scope. We do not know the effects of leucine in production and release of sorotonin.
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Re: It was once believed that the brain was independent of meta  [#permalink]

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New post 08 May 2019, 02:34
9:10. All correct. Easy to follow and similar to other passages in anatomy.
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Re: It was once believed that the brain was independent of meta   [#permalink] 08 May 2019, 02:34
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