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.

　　參考答案：

　　1. D 主旨題。本題的問題是“本文主要是 關(guān)于什么?”文章第一段首先提到動物的氧化新陳代謝率對其生存方式造成的影響，隨后引出了無氧糖酵解這個(gè)概念;第二段解釋了無氧糖酵解，第三段介紹了無氧糖酵解的局限性以及對動物的生存產(chǎn)生的影響。這說明[D]“解釋無氧糖酵解及其對動物生存產(chǎn)生的影響”可以表達(dá)本文的主題，為正確答案。文中沒有提到有關(guān)無氧糖酵解的錯(cuò)誤觀念和新假說，所以[A]“反駁有關(guān)無氧糖酵解的一個(gè)錯(cuò)誤概念”和[B]“介紹有關(guān)無氧糖酵解的一種新假說”屬于無中生有;[C]“描述無氧糖酵解的局限性”只是第三段的內(nèi)容，比較片面，不能表達(dá)本文的主題。

　　2. D 細(xì)節(jié)題。本題的問題是“根據(jù)作者的觀點(diǎn)，糖原質(zhì)對于無氧糖酵解的過程至關(guān)重要。因?yàn)樘窃�質(zhì)——”。題干中的“glycogen”出自文章第二段第一句話中，表明本題與第二段有關(guān)。第二段在解釋無氧糖酵解時(shí)提到，無氧糖酵解可以產(chǎn)生能量是糖原質(zhì)存在的作用，其能量是由、肌糖原質(zhì)分解成乳酸和三磷酸腺苷而產(chǎn)生的，而能量的供應(yīng)者是三磷酸腺苷。這說明，糖原質(zhì)是無氧糖酵解的能量來源，也就是三磷酸腺苷的來源。[D]“是從中獲得三磷酸腺苷的物質(zhì)”是對文章第二段中“through the breakdown of muscle glycogen into lactic acid and adenosine triphosphate(ATP)”這句話的改寫，為正確答案。文中沒有提到加大三磷酸腺苷的需求和降低其含量的問題，所以[A]“加大了生物體對三磷酸腺苷的需求”和[B]“降低了組織中三磷酸腺苷的含量”屬于無中生有;[C]“是三磷酸腺苷的氧化新陳代謝生產(chǎn)的抑制者”與文意相反。

　　3. D 推論題。本題的問題是“文中暗示，脊椎動物的總無氧能源儲備與其體型大小相稱，因?yàn)?”。題干中的“are proportional to its size”出自文章第二段第三句話中，表明本題與第二段有關(guān)。第二段提到，糖原質(zhì)大約占脊椎動物肌肉凈重的0.5%，所以脊椎動物的無氧性能量儲存同其體型的大小相稱;隨后列舉的恐龍例if-解釋了其中的原翻：由于恐龍的體型龐大，所以它可以通過無氧糖酵解在瞬間產(chǎn)生很大的能量。由此可知。肌肉越多，糖原質(zhì)的含量就越多，而只有體型越大，肌肉才越多。[D]“脊椎動物體內(nèi)的肌肉組織量同其體型大小直接相關(guān)”是對文章第二段中“the anaerobic energy reserves of a vertebrate are proportional to the size of the animal”這句話的改寫，為正確答案。[A]“較大的脊椎動物儲備的能量比較小的脊椎動物多”是針對文中“the anaerobic energy reserves of a vertebrate are proportional to the size of the animal”這句話設(shè)置的干擾項(xiàng)。而文中說的是脊椎動物的無氧性能量儲存，并不是脊椎動物儲備的能量，屬于偷換概念，所以不對;文中只提到了消耗食物和水的問題，沒有提到消耗氧氣的問題，所以[B]“較大的脊椎動物每單位體重消耗的氧氣比較小的脊椎動物少”屬于偷換概念;[C]“脊椎動物消耗食物的能力是其體型的作用”是對文中“The amount of energy that can be produced anaerobically is a functi0n of the amount of glycogen present”這句話的篡改，與文意不符。

　　4. B 細(xì)節(jié)題。本題的問題是“根據(jù)本文的觀點(diǎn)，無氧糖酵解的一個(gè)主要局限性就是，‘它能夠 ”。題干中的“l(fā)imitation”出自文章第三段第一句話中，表明本題與第三段有關(guān)。第三段解釋了補(bǔ)償?shù)木窒扌�，指出，動物由于無氧糖酵解所導(dǎo)致的大量能量消耗必須得到補(bǔ)償;隨后舉例說，小地鼠在幾分鐘內(nèi)就能補(bǔ)償其最劇烈運(yùn)動所消耗的糖原質(zhì)。但體型龐大的恐龍卻需要三個(gè)多星期才能完成補(bǔ)償。這說明，其主要局限性就是大型動物的補(bǔ)償期時(shí)間長。[B]“使大型動物必須有長時(shí)間的補(bǔ)償期”是對文中“the gigantic dinosaur would have required more than three weeks”這句話的改寫，為正確答案。文中提到“reconvert”時(shí)是說“一陣劇烈運(yùn)動結(jié)束后，體液中乳酸的含量就高，這使得大型動物容易受到攻擊，直到乳酸通過氧化新陳代謝由肝臟再次轉(zhuǎn)化成葡萄糖”，說明[A]“在大型動物體內(nèi)生產(chǎn)的乳酸比肝臟可以再次轉(zhuǎn)化的乳酸多”屬于偷換概念;[C]“使能量減少的速度慢于大型動物使用能量的速度”與文意相反;[D]“消耗所有可以利用的糖原質(zhì)，不管需不需要”與第三段最后一句話的意思不符。

　　5. A 推論題。本文的問題是“作者最可能針對下面哪類聽眾發(fā)表演說?”作者主要是介紹無氧糖酵解對動物的生存產(chǎn)生的影響，他的解釋清楚易懂，沒有提到深?yuàn)W難懂的知識。由此可知，作者最可能是針對初學(xué)動物學(xué)的學(xué)生這類讀者。[A]“動物生理學(xué)入門課的大學(xué)生”為正確答案。本文只是提到了無氧糖酵解，沒有介紹如何發(fā)現(xiàn)它，并且所介紹的知識并不深?yuàn)W，所以[B]“研究無氧糖酵解發(fā)現(xiàn)的歷史科學(xué)家”不可能是作者針對的聽眾;本文并沒有提到解剖學(xué)方面的知識，所以[C]“專業(yè)研究比較解剖學(xué)的研究生”屬于無中生有;本文列舉恐龍的例子只是為了說明無氧性能量儲存同動物體型的大小相稱這個(gè)問題，并沒有提到其他史前動物，不可能吸引對史前動物感興趣的動物學(xué)家，所以[D]“對史前動物感興趣的動物學(xué)家”不可能是作者針對的聽眾。

　　全文譯文

　　長期以來，人們一直知道，任何動物的氧化新陳代謝率(利用氧氣將食物轉(zhuǎn)化為能量的過程)都對其生存方式有著深刻的影響。比如，小型動物的高新陳代謝率可以給它們的每個(gè)重量單位提供持續(xù)不變的力量和活力，但是，這要以不斷消耗食物和水為代價(jià)。由于大型動物的新陳代謝率相對較低，所以它們可以依賴時(shí)有時(shí)無的食物供給很好地生存，但是其每克體重生產(chǎn)的新陳代謝能量很少。1)因此，如果只考慮氧化新陳代謝率，那么人們可能認(rèn)為，更小、更活躍的動物可以捕食較大型的動物，至少如果它們發(fā)動群體攻擊的話會如此;也許它們可以做到這一點(diǎn)，如果不是因?yàn)闊o氧糖酵解這個(gè)重要的補(bǔ)償機(jī)制的話。

　　無氧糖酵解是一個(gè)在無氧狀態(tài)下通過把肌糖原質(zhì)分解成乳酸和三磷酸腺苷(能量供應(yīng)者)從而產(chǎn)生能量的過程。無氧糖酵解可以產(chǎn)生能量是糖原質(zhì)存在的作用——糖原質(zhì)大約占所有脊椎動物肌肉凈重的0.5%.因此，脊椎動物的無氧性能量儲存同其體型的大小相稱。2)比如-如果某些食肉動物攻擊了一只100噸重的恐龍。由于這類恐龍通常行動遲緩。所以它可能通過無氧糖酵解在瞬間產(chǎn)生3，000個(gè)人進(jìn)行氧化新陳代謝所能產(chǎn)生的最大能量。這就解釋了許多大型動物是如何設(shè)法與它們周圍更活躍的動物競爭的原因：給低氧化新陳代謝率的補(bǔ)償就是糖酵解。

　　不過，這種補(bǔ)償有局限性。任何動物的糖原質(zhì)儲存最多只夠維持大約兩分鐘的最劇烈運(yùn)動，之后就只剩下正常的氧化新陳代謝能量來源。3)一陣劇烈運(yùn)動結(jié)束后，體液中乳酸的含量就會高，這使得大型動物容易受到攻擊，直到乳酸通過氧化新陳代謝由肝臟再次轉(zhuǎn)化成葡萄糖，然后，葡萄糖(部分)被送回到肌肉進(jìn)行糖原質(zhì)的再合成。在這個(gè)過程中，動物由于無氧糖酵解所導(dǎo)致的大量能量消耗必須得到補(bǔ)償——按比例來說，較大脊椎動物的這種消耗比較小動物大得多。比如，小地鼠在幾分鐘內(nèi)就能補(bǔ)償其最劇烈運(yùn)動所消耗的糖原質(zhì)，但是體型龐大的恐龍卻需要三個(gè)多星期才能完成補(bǔ)償。似乎可能的是，大型脊椎動物這種冗長的補(bǔ)償時(shí)間被證明對其生存非常不利。幸運(yùn)的是，只有在需要時(shí)才會使用肌糖原質(zhì)，盡管那樣，也只有在需要一定量的糖原質(zhì)時(shí)才如此。只有在驚恐或者生死搏斗時(shí)，所有的能量儲備才會被消耗。

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