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Director
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The chemical adenosine is released by brain cells when those [#permalink]
 31 Jan 2007, 07:28
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The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases. Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep.
Which of the following, if true, provides the most support for the researchers’
hypothesis?
A. Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large.
B. Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
C. Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.
D. Some areas of the brain that are relatively inactive nonetheless release
some adenosine.
E. Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.
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Senior Manager
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This is a good one... Is the Answer A?
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Director
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This would be B for me.
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Manager
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B should be answer. It proves that caffeine prevents adenosine hence causing wakefulness which suggest that it is adenosine which caused sleepiness. Good argument in support of theory.
Please tell OA.
A --> If concentration of adenosine is high even after waking up from a good sleep, It refutes proposed theory.
B --> proves that caffeine prevents adenosine hence causing wakefulness
C --> Does not relate with theory. Does not matter.
D --> If inactive cells also emit adenosine, theory fails.
E ---> talks about other factor causing wakefulness.
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aurobindo wrote: The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases. Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep.
Which of the following, if true, provides the most support for the researchers’
hypothesis?
A. Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large.
B. Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
C. Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.
D. Some areas of the brain that are relatively inactive nonetheless release
some adenosine.
E. Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.
Initially went for A, but I'll go with B.
Hypothesis is that during wakefulness the cumulative binding of Ad. to sites in the brain, built up from wakeful hours, is what makes you sleepy.
B supports the hyp. by saying that Caffeine makes us awake by preventing the action that makes us sleepy (binding of Adenosine to cells)
A is very close but I think that AFTER long periods of sleep the number of bound cells would decrease because you are going to wake up. I could argue for A too, and probably would have chosen A on test day.
Can anyone argue the reasons for their choice? I'm a little torn b/w A and B
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aurobindo wrote: The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases. Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep.
The para-phrased argument is similar to the following.
Adenosine is released by active brain cells
As adenosine level increases, they are bound to the brain cells.
Researchers say that the binding of adenosines to the brain cells in a large number of cells causes onset of sleep. --> Restated as 'Adenosine when bound to the brain makes the brain cell less active and causes the onset of sleep.'
We can substantiate the hypothesis by demonstrating that sleep can be prevented by preventing the binding of adenosines to brain cells.
According to B,
B. Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
B strengthens the hypothesis. No other answer comes close. B is my pick.
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Director
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Thanks Guys. The OA is B.
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