大全41/63(生物类）

liuyanjia

[url=]Passage 41 (41/63[/url])

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 in brain neurons of the neurotransmitter serotonin (serotonin: n.含于血液中的复合胺) (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 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 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 blood-tryptophan increases. In later studies we 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. 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 serotonin in the brain increased after the meal.

Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. 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 consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein in the meal, 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. Thus the more protein in a meal, the less serotonin subsequently produced and released.

生物类的文章真让我头疼．真搞不懂新陈代谢跟下面的两段之间有什么关系．

有谁能帮我分析分析这篇文章啊

anilolive

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



(B) Meals consisting almost exclusively of carbohydrates



(C) Meals that would elicit insulin secretion



(D) Meals that had very low concentrations of tyrosine（A）





(E) Meals that had very low concentrations of leucine



请问一下这题



题目中说的not adequately producing and releasing serotonin...这个很怪异.是More or less呢



我对题目的分析是



DE肯定定是对的...因为这两个都是一样的



我觉得B和C是对立的.



所以我选的是B



请NN帮忙帮忙~~~



阅读做的好郁闷啊...

cclovelife

我也选B，不知道为什么选A!文章的最后一句写了：Thus the more protein in a meal, the less serotonin subsequently produced and released.请nn出来指点！！

STshadow

)

It was once believed that the brain was independent of metabolic processes occurring elsewhere  ...
liuyanjia 发表于 2013-5-9 06:43

高中生物忘差不多了吧？嗬嗬，其实有点印象的话这篇不难懂啊，代谢的过程就是蛋白质……一堆东西的转化过程嘛。这篇文章是研究了其中一个步骤。

仅此而已

STshadow

我也选B，不知道为什么选A!文章的最后一句写了：Thus the more protein in a meal, the less serotonin sub ...
cclovelife 发表于 2013-5-10 06:57

你都找到这句了，怎么还不知道选哪个啊？病人本来就 serotonin不足，这句说protein多了，产生和释放serotonin就少，所以不能给他用protein啊

waytouing

你都找到这句了，怎么还不知道选哪个啊？病人本来就 serotonin不足，这句说protein多了，产生和释放s ...
STshadow 发表于 2013-5-11 10:24

That's why I don't choose A. Meals consisting almost exclusively of protein would be likely to be a potentialsource of aid to a patient who was not adequatelyproducing and releasing serotonin.

So why A?

I think it's B. Carbonhydrates helps people to create serotonin, so meals consisting almost exclusively of carbohydrates would be LEAST likely to be a potentialsource of aid to a patient who was not adequatelyproducing and releasing serotonin.

Open to discuss.

imddung

up up up ,同问！
与楼上意见一致，是不是答案错了？