問題詳情

C.Fungi, of which there are 100,000 species, including yeast and other single-celled organisms, were formerly classified asmembers of the plant kingdom. The principal reason for this is that none of them possess chlorophyll, and since they cannotsynthesize their own carbohydrates, they obtain their supplies either from breakdown of dead organic matter or from otherliving organisms. Furthermore, the walls of fungal cells are not made of cellulose, as those of plants are, but of anothercomplex sugarlike polymer called chitin, the material from which the hard outer skeletons of shrimps, spiders, and insects aremade. The difference between the chemical composition of the cell walls of fungi and those of plants is of enormousimportance because it enables the tips of the growing hyphae, the threadlike cells of fungus, to secrete enzymes that breakdown the walls of plant cells without having any effect on those of the fungus itself. It is these cellulose-destroying enzymesthat enable fungi to attack anything made from wood, wood pulp, cotton, flax, or other plant material.    The destructive power of fungi is impressive. They are a major cause of structural damage to building timbers, a cause ofdiseases in animals and humans, and one of the greatest cause of agricultural losses. Entire crops can be wiped out by fungalattacks both before and after harvesting. Some fungi can grow at +50C, while others can grow at -5C, so even food in coldstorage may not be completely safe from them. On the other hand, fungi bring about the decomposition of dead organicmatter, thus enriching the soil and returning carbon dioxide to the atmosphere. They also enter into a number of mutuallybeneficial relationship with plants and other organisms. In addition, fungi are the source of many of the most potent antibioticsused in clinical medicine including penicillin.
41. What does paragraph 1 mainly discuss?
(A) Differences between simple and complex fungi.
(B) Functions of chlorophyll and carbohydrates in fungi.
(C) Differences between fungi and plants.
(D) Functions of the growing hyphae in the walls of fungal cells.

參考答案

答案：C
難度：適中0.5
統計：A(2),B(3),C(6),D(0),E(0)

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