2016年考研理学类英语阅读理解模拟题及答案(2)

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

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