It has long been known that the rate of oxidative metabolism (the process that uses oxygen to convert food into energy) in any animal has a profound effect on its living patterns. The high metabolic rate of small animals， for example， gives them sustained power and activity per unit of weight， but at the cost of requiring constant consumption of food and water. Very large animals， with their relatively low metabolic rates， can survive well on a sporadic food supply， but can gen- erate little metabolic energy per gram of body weight. If only oxidative metabolic rate is considered， there- fore， one might assume that smaller， more active， animals could prey on larger ones， at least if they attacked in groups. Perhaps they could if it were not for anaerobic glycolysis， the great equalizer.
Anaerobic glcolysis is a process in which energy is produced， without oxygen， through the breakdown of muscle glycogen into lactic acid and adenosine tri- phosphate (ATP)， the energy provider. The amount of energy that can be produced anaerobically is a function of the amount of glycogen present-in all vertebrates about 0.5 percent of their muscles' wet weight. Thus the anaerobic energy reserves of a verte- brate are proportional to the size of the animal. If， for example， some predators had attacked a 100-ton dinosaur， normally torpid， the dinosaur would have been able to generate almost instantaneously， via anaerobic glycolysis， the energy of 3，000 humans at maximum oxidative metabolic energy production. This explains how many large species have managed to compete with their more active neighbors： the compensation for a low oxidative metabolic rate is glycolysis.
There are limitations， however， to this compensa- tion. The glycogen reserves of any animal are good， at most， for only about two minutes at maximum effort， after which only the normal oxidative metabolic source of energy remains. With the conclusion of a burst of activity， the lactic acid level is high in the body fluids， leaving the large animal vulnerable to attack until the acid is reconverted， via oxidative metabolism， by the liver into glucose， which is then sent (in part) back to the muscles for glycogen resyn- thesis. During this process the enormous energy debt that the animal has run up through anaerobic glycolysis must be repaid， a debt that is proportionally much greater for the larger vertebrates than for the smaller ones. Whereas the tiny shrew can replace in minutes the glycogen used for maximum effort， for example， the gigantic dinosaur would have required more than three weeks. It might seem that this inter- minably long recovery time in a large vertebrate would prove a grave disadvantage for survival. Fortunately， muscle glycogen is used only when needed and even then only in whatever quantity is necessary. Only in times of panic or during mortal combat would the entire reserves be consumed.
1. What is the text mainly about?。
[A] refute a misconception about anaerobic glycolysis.
[B] introduce a new hypothesis about anaerobic glycolysis.
[C] describe the limitations of anaerobic glycolysis.
[D] explain anaerobic glycolysis and its effects on animal survival.
2. According to the author， glycogen is crucial to the process of anaerobic glyrolysis because glycogen
[A] increases the organism‘s need for ATP.
[B] reduces the amount of ATP in the tissues.
[C] is an inhibitor of the oxidative metabolic production of ATP.
[D] is the material form which ATP is derived.
3. It is implied that the total anaerobic energy reserves of a vertebrate are proportional to its size because
[A] larger vertebrate conserve more energy than smaller vertebrates.
[B] larger vertebrates use less oxygen per unit weight than smaller vertebrates.
[C] the ability of a vertebrate to consume food is a function of its size.
[D]the amount of muscle tissue in a vertebrate is directly related to its size，
4. According to the text， a major limitation of anaerobic glycolysis is that it can
[A] produce in large animals more lactic acid than the liver can safely reconvert.
[B] necessitate a dangerously long recovery period in large animals.
[C] reduce energy more slowly than it can be used by large animals.
[D]consume all of the available glycogen regardless of need.
5. Which of the following audiences is the author most probably addressing?
[A] College students in an introductory course on animal physiology.
[B] Historians of science investigating the discovery of anaerobic glycolysis.
[C] Graduate students with specialized training in comparative anatomy.
[D] Zoologists interested in prehistoric animals.
1. D 主旨题。本题的问题是“本文主要是 关于什么?”文章第一段首先提到动物的氧化新陈代谢率对其生存方式造成的影响，随后引出了无氧糖酵解这个概念;第二段解释了无氧糖酵解，第三段介绍了无氧糖酵解的局限性以及对动物的生存产生的影响。这说明[D]“解释无氧糖酵解及其对动物生存产生的影响”可以表达本文的主题，为正确答案。文中没有提到有关无氧糖酵解的错误观念和新假说，所以[A]“反驳有关无氧糖酵解的一个错误概念”和[B]“介绍有关无氧糖酵解的一种新假说”属于无中生有;[C]“描述无氧糖酵解的局限性”只是第三段的内容，比较片面，不能表达本文的主题。
2. D 细节题。本题的问题是“根据作者的观点，糖原质对于无氧糖酵解的过程至关重要。因为糖原质——”。题干中的“glycogen”出自文章第二段第一句话中，表明本题与第二段有关。第二段在解释无氧糖酵解时提到，无氧糖酵解可以产生能量是糖原质存在的作用，其能量是由、肌糖原质分解成乳酸和三磷酸腺苷而产生的，而能量的供应者是三磷酸腺苷。这说明，糖原质是无氧糖酵解的能量来源，也就是三磷酸腺苷的来源。[D]“是从中获得三磷酸腺苷的物质”是对文章第二段中“through the breakdown of muscle glycogen into lactic acid and adenosine triphosphate(ATP)”这句话的改写，为正确答案。文中没有提到加大三磷酸腺苷的需求和降低其含量的问题，所以[A]“加大了生物体对三磷酸腺苷的需求”和[B]“降低了组织中三磷酸腺苷的含量”属于无中生有;[C]“是三磷酸腺苷的氧化新陈代谢生产的抑制者”与文意相反。
3. D 推论题。本题的问题是“文中暗示，脊椎动物的总无氧能源储备与其体型大小相称，因为 ”。题干中的“are proportional to its size”出自文章第二段第三句话中，表明本题与第二段有关。第二段提到，糖原质大约占脊椎动物肌肉净重的0.5%，所以脊椎动物的无氧性能量储存同其体型的大小相称;随后列举的恐龙例if-解释了其中的原翻：由于恐龙的体型庞大，所以它可以通过无氧糖酵解在瞬间产生很大的能量。由此可知。肌肉越多，糖原质的含量就越多，而只有体型越大，肌肉才越多。[D]“脊椎动物体内的肌肉组织量同其体型大小直接相关”是对文章第二段中“the anaerobic energy reserves of a vertebrate are proportional to the size of the animal”这句话的改写，为正确答案。[A]“较大的脊椎动物储备的能量比较小的脊椎动物多”是针对文中“the anaerobic energy reserves of a vertebrate are proportional to the size of the animal”这句话设置的干扰项。而文中说的是脊椎动物的无氧性能量储存，并不是脊椎动物储备的能量，属于偷换概念，所以不对;文中只提到了消耗食物和水的问题，没有提到消耗氧气的问题，所以[B]“较大的脊椎动物每单位体重消耗的氧气比较小的脊椎动物少”属于偷换概念;[C]“脊椎动物消耗食物的能力是其体型的作用”是对文中“The amount of energy that can be produced anaerobically is a functi0n of the amount of glycogen present”这句话的篡改，与文意不符。
4. B 细节题。本题的问题是“根据本文的观点，无氧糖酵解的一个主要局限性就是，‘它能够 ”。题干中的“limitation”出自文章第三段第一句话中，表明本题与第三段有关。第三段解释了补偿的局限性，指出，动物由于无氧糖酵解所导致的大量能量消耗必须得到补偿;随后举例说，小地鼠在几分钟内就能补偿其最剧烈运动所消耗的糖原质。但体型庞大的恐龙却需要三个多星期才能完成补偿。这说明，其主要局限性就是大型动物的补偿期时间长。[B]“使大型动物必须有长时间的补偿期”是对文中“the gigantic dinosaur would have required more than three weeks”这句话的改写，为正确答案。文中提到“reconvert”时是说“一阵剧烈运动结束后，体液中乳酸的含量就高，这使得大型动物容易受到攻击，直到乳酸通过氧化新陈代谢由肝脏再次转化成葡萄糖”，说明[A]“在大型动物体内生产的乳酸比肝脏可以再次转化的乳酸多”属于偷换概念;[C]“使能量减少的速度慢于大型动物使用能量的速度”与文意相反;[D]“消耗所有可以利用的糖原质，不管需不需要”与第三段最后一句话的意思不符。
5. A 推论题。本文的问题是“作者最可能针对下面哪类听众发表演说?”作者主要是介绍无氧糖酵解对动物的生存产生的影响，他的解释清楚易懂，没有提到深奥难懂的知识。由此可知，作者最可能是针对初学动物学的学生这类读者。[A]“动物生理学入门课的大学生”为正确答案。本文只是提到了无氧糖酵解，没有介绍如何发现它，并且所介绍的知识并不深奥，所以[B]“研究无氧糖酵解发现的历史科学家”不可能是作者针对的听众;本文并没有提到解剖学方面的知识，所以[C]“专业研究比较解剖学的研究生”属于无中生有;本文列举恐龙的例子只是为了说明无氧性能量储存同动物体型的大小相称这个问题，并没有提到其他史前动物，不可能吸引对史前动物感兴趣的动物学家，所以[D]“对史前动物感兴趣的动物学家”不可能是作者针对的听众。
全文译文
长期以来，人们一直知道，任何动物的氧化新陈代谢率(利用氧气将食物转化为能量的过程)都对其生存方式有着深刻的影响。比如，小型动物的高新陈代谢率可以给它们的每个重量单位提供持续不变的力量和活力，但是，这要以不断消耗食物和水为代价。由于大型动物的新陈代谢率相对较低，所以它们可以依赖时有时无的食物供给很好地生存，但是其每克体重生产的新陈代谢能量很少。1)因此，如果只考虑氧化新陈代谢率，那么人们可能认为，更小、更活跃的动物可以捕食较大型的动物，至少如果它们发动群体攻击的话会如此;也许它们可以做到这一点，如果不是因为无氧糖酵解这个重要的补偿机制的话。
无氧糖酵解是一个在无氧状态下通过把肌糖原质分解成乳酸和三磷酸腺苷(能量供应者)从而产生能量的过程。无氧糖酵解可以产生能量是糖原质存在的作用——糖原质大约占所有脊椎动物肌肉净重的0.5%.因此，脊椎动物的无氧性能量储存同其体型的大小相称。2)比如-如果某些食肉动物攻击了一只100吨重的恐龙。由于这类恐龙通常行动迟缓。所以它可能通过无氧糖酵解在瞬间产生3，000个人进行氧化新陈代谢所能产生的最大能量。这就解释了许多大型动物是如何设法与它们周围更活跃的动物竞争的原因：给低氧化新陈代谢率的补偿就是糖酵解。
不过，这种补偿有局限性。任何动物的糖原质储存最多只够维持大约两分钟的最剧烈运动，之后就只剩下正常的氧化新陈代谢能量来源。3)一阵剧烈运动结束后，体液中乳酸的含量就会高，这使得大型动物容易受到攻击，直到乳酸通过氧化新陈代谢由肝脏再次转化成葡萄糖，然后，葡萄糖(部分)被送回到肌肉进行糖原质的再合成。在这个过程中，动物由于无氧糖酵解所导致的大量能量消耗必须得到补偿——按比例来说，较大脊椎动物的这种消耗比较小动物大得多。比如，小地鼠在几分钟内就能补偿其最剧烈运动所消耗的糖原质，但是体型庞大的恐龙却需要三个多星期才能完成补偿。似乎可能的是，大型脊椎动物这种冗长的补偿时间被证明对其生存非常不利。幸运的是，只有在需要时才会使用肌糖原质，尽管那样，也只有在需要一定量的糖原质时才如此。只有在惊恐或者生死搏斗时，所有的能量储备才会被消耗。
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