The whole biosphere, like the individual organisms that live inside it, exists in a chemically dynamic state. In this homeostatic system, a great number of organic compounds are synthesized, transformed, and decomposed continuously; together, these processes constitute the major parts of the carbon cycle. For the smooth operation of this cycle, degradation is just as important as synthesis: the green plants produce great quantities of polymers, such as cellulose, and innumerable other compounds like alkaloids, terpenes, and flavonoids, that green plants cannot use as sources of energy during respiration. The release of the carbon in these compounds for recycling depends almost entirely on the action of both aerobic and anaerobic bacteria and certain types of fungi. Some bacteria and fungi possess the unique and extremely important biochemical asset of being able to catalyze the oxidation of numerous inert products, thereby initiating reaction sequences that produce carbon dioxide and so return much carbon to a form that actively enters into life cycles once again.
26. The author implies that which of the following is the primary reason that degradation is as important as synthesis to the smooth operation of the carbon cycle?
(A) Most of the polymers and organic compounds found in the plant kingdom are chemically unstable.
(B) The synthesis of some organic material deprives life processes of an energy source.
(C) Decomposition permits the recycling of carbon that would otherwise be fixed in certain substances.
(D) Many organisms cannot use plants as a source of food, but can feed on bacteria and fungi.
(E) Bacteria and fungi could not survive if some carbon compounds were not degraded.
|GRE 应考班||310-320分||强化训练 短期提高||报名|