問題詳情

   It has long been known that the rate of oxidative metabolism (the process thatuses oxygen to convert food into energy) in any animal has a profound effect on itsliving patterns. The high metabolic rate of small animals, for example, gives themsustained power and activity per unit of weight, but at the cost of requiring constantconsumption of food and water. Very large animals, with their relatively lowmetabolic rates, can survive well on a sporadic food supply, but can generate littlemetabolic energy per gram of body weight. If only oxidative metabolic rate isconsidered, therefore, one might assume that smaller, more active, animals could preyon larger ones, at least if they attacked in groups. Perhaps they could if it were not foranaerobic glycolysis, the great equalizer.    Anaerobic glycolysis is a process in which energy is produced, withoutoxygen, through the breakdown of muscle glycogen into lactic acid and adenosinetriphosphate (ATP), the energy provider. The amount of energy that can be producedanaerobically is a function of the amount of glycogen present—in all vertebratesabout 0.5 percent of their muscles’ wet weight. Thus the anaerobic energy reserves ofa vertebrate are proportional to the size of the animal. If, for example, some predatorshad attacked a 100-ton dinosaur, normally torpid, the dinosaur would have been ableto generate almost instantaneously, via anaerobic glycolysis, the energy of 3,000humans at maximum oxidative metabolic energy production. This explains how manylarge species have managed to compete with their more active neighbors: thecompensation for a low oxidative metabolic rate is glycolysis.    There are limitations, however, to this compensation. The glycogen reservesof any animal are good, at most, for only about two minutes at maximum effort, afterwhich only the normal oxidative metabolic source of energy remains. With theconclusion 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, viaoxidative metabolism, by the liver into glucose, which is then sent (in part) back tothe muscles for glycogen resynthesis. During this process the enormous energy debtthat the animal has run up through anaerobic glycolysis must be repaid, a debt that isproportionally 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. Itmight seem that this interminably long recovery time in a large vertebrate wouldprove a grave disadvantage for survival. Fortunately, muscle glycogen is used onlywhen needed and even then only in whatever quantity is necessary. Only in times ofpanic or during mortal combat would the entire reserves be consumed.
10. The primary purpose of the passage is to
(A) refute a misconception about anaerobic glycolysis
(B) introduce a new hypothesis about anaerobic glycolysis
(C) describe the limitations of anaerobic glycolysis
(D) analyze the chemistry of anaerobic glycolysis and its similarity to oxidativemetabolism
(E) explain anaerobic glycolysis and its effects on animal survival

參考答案

答案：E
難度：適中0.5
統計：A(0),B(0),C(0),D(0),E(0)

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