GMAT考试阅读资料(七)b
文章来源: 文章作者: 发布时间:2008-10-25 06:04 字体: [ ]  进入论坛
(单词翻译:双击或拖选)
Passage 38   It was once believed that the brain was independent of metabolic1 processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neuro-(5) transmitter 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 the increase in serotonin observed in rats given a large injec-(10)tion 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 elevations2 occurred in blood tryptophan,brain tryptophan, and brain serotonin levels. These find-(15)ings suggested that the production and release of sero-tonin 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(20) and in serotonin levels. We then decided3 to see whether the secretion4 of the animal’s own insulin similarly affected5 serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit6 insulin secre-tion. As we had hypothesized, the blood tryptophan(25) level and the concentrations of tryptophan  serotonin in the brain increased after the meal.
  Surprisingly, however, when we added a largeamount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains tryptophan,(30)why should it depress brain tryptophan levels? The answer lies in the mechanism7 that provides blood tryp-tophan 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(35) 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(40) 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.
  1. Which of the following titles best summarizes the contents of the passage?
   (A) Neurotransmitters: Their Crucial Function in Cellular8 Communication
   (B) Diet and Survival: An Old Relationship Reexamined
   (C) The Blood Supply and the Brain: A Reciprocal Dependence9
   (D) Amino Acids and Neurotransmitters: The Connection Between Serotonin Levels and Tyrosine
   (E) The Effects of Food Intake10 on the Production and Release of Serotonin:Some Recent Findings
  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
   (B) concentration of serotonin in the brain before a meal
   (C) concentration of leucine in the blood rather than on 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 present in the brain before a meal
  3. 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 of tryptophan
  4. According to the passage, one reason that the authors gave rats carbohydrates11 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 secreted12 by the body
   (E) compare the effect of carbohydrates with the effect of proteins
  5. According to 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) ratio of 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 kind that the rat will produce and release
   (E) number of amino acids the rat‘s blood will contain
  6. The authors‘ discussion of the “mechanism that provides blood tryptophan to the brain cells” (lines 31-32) is meant to
   (A) stimulate13 further research studies
   (B) summarize an area of scientific investigation14
   (C) help explain why a particular research finding was obtained
   (D) provide supporting evidence for a controversial scientific theory
   (E) refute the conclusions of a previously15 mentioned research study
  7. 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
  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
   (E) Meals that had very low concentrations of leucine
  9. It can be inferred from the passage that the authors initially16 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.


点击收听单词发音收听单词发音  

1 metabolic 2R4z1     
adj.新陈代谢的
参考例句:
  1. Impressive metabolic alternations have been undergone during embryogenesis.在胚胎发生期间经历了深刻的代谢变化。
  2. A number of intoxicants are associated with metabolic acidosis.许多毒性物质可引起代谢性酸中毒。
2 elevations cb4bbe1b6e824c996fd92d711884a9f2     
(水平或数量)提高( elevation的名词复数 ); 高地; 海拔; 提升
参考例句:
  1. Weight of the crust changes as elevations are eroded and materials are deposited elsewhere. 当高地受到侵蚀,物质沉积到别的地方时,地壳的重量就改变。
  2. All deck elevations are on the top of structural beams. 所有甲板标高线均指结构梁顶线。
3 decided lvqzZd     
adj.决定了的,坚决的;明显的,明确的
参考例句:
  1. This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
  2. There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。
4 secretion QDozG     
n.分泌
参考例句:
  1. Is there much secretion from your eyes?你眼里的分泌物多吗?
  2. In addition,excessive secretion of oil,water scarcity are also major factors.除此之外,油脂分泌过盛、缺水也都是主要因素。
5 affected TzUzg0     
adj.不自然的,假装的
参考例句:
  1. She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
  2. His manners are affected.他的态度不自然。
6 elicit R8ByG     
v.引出,抽出,引起
参考例句:
  1. It was designed to elicit the best thinking within the government. 机构的设置是为了在政府内部集思广益。
  2. Don't try to elicit business secrets from me. I won't tell you anything. 你休想从我这里套问出我们的商业机密, 我什么都不会告诉你的。
7 mechanism zCWxr     
n.机械装置;机构,结构
参考例句:
  1. The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  2. The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
8 cellular aU1yo     
adj.移动的;细胞的,由细胞组成的
参考例句:
  1. She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。
  2. Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。
9 dependence 3wsx9     
n.依靠,依赖;信任,信赖;隶属
参考例句:
  1. Doctors keep trying to break her dependence of the drug.医生们尽力使她戒除毒瘾。
  2. He was freed from financial dependence on his parents.他在经济上摆脱了对父母的依赖。
10 intake 44cyQ     
n.吸入,纳入;进气口,入口
参考例句:
  1. Reduce your salt intake.减少盐的摄入量。
  2. There was a horrified intake of breath from every child.所有的孩子都害怕地倒抽了一口凉气。
11 carbohydrates 001f0186d1ea717492c413ca718f2635     
n.碳水化合物,糖类( carbohydrate的名词复数 );淀粉质或糖类食物
参考例句:
  1. The plant uses the carbohydrates to make cellulose. 植物用碳水化合物制造纤维素。 来自《简明英汉词典》
  2. All carbohydrates originate from plants. 所有的碳水化合物均来自植物。 来自辞典例句
12 secreted a4714b3ddc8420a17efed0cdc6ce32bb     
v.(尤指动物或植物器官)分泌( secrete的过去式和过去分词 );隐匿,隐藏
参考例句:
  1. Insulin is secreted by the pancreas. 胰岛素是胰腺分泌的。
  2. He secreted his winnings in a drawer. 他把赢来的钱藏在抽届里。 来自《简明英汉词典》
13 stimulate wuSwL     
vt.刺激,使兴奋;激励,使…振奋
参考例句:
  1. Your encouragement will stimulate me to further efforts.你的鼓励会激发我进一步努力。
  2. Success will stimulate the people for fresh efforts.成功能鼓舞人们去作新的努力。
14 investigation MRKzq     
n.调查,调查研究
参考例句:
  1. In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
  2. He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。
15 previously bkzzzC     
adv.以前,先前(地)
参考例句:
  1. The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  2. Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
16 initially 273xZ     
adv.最初,开始
参考例句:
  1. The ban was initially opposed by the US.这一禁令首先遭到美国的反对。
  2. Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。
TAG标签:
发表评论
请自觉遵守互联网相关的政策法规,严禁发布色情、暴力、反动的言论。
评价:
表情:
验证码:点击我更换图片

鸿运国际娱乐官网

百度360搜索搜狗搜索