【备考每日练】GRE阅读题之环境保护问题

2015年12月07日10:15 来源：小站整理: 参与（0）阅读（4729）

摘要：名师心血之作，考生必备最完美阅读资料，打造你的完美GRE阅读，走过路过不要错过，分数掌握在自己手中，做自己的主宰，每日练一练，分数节节高，你值得拥有，且看且珍惜！GRE必胜！

名师心血之作，考生必备最完美阅读资料，让GRE阅读更加完美，打造你的完美GRE分数，走过路过不要错过，命运掌握在自己手中，GRE掌握在自己手中，每日练一练，分数节节高，你值得拥有，且看且珍惜!GRE必胜!

每日一练

Although pathogenic organisms constantly alight on the skin, they find it a very unfavorable environment and, in the absence of injury, have great difficulty colonizing it. This “self-sterilizing” capacity of the skin results from the tendency of all well-developed ecosystems toward homeostasis, or the maintenance of the status quo.

Species that typically live in soil, water, and elsewhere rarely multiply on the skin. Undamaged skin is also unfavorable to most human pathogens. The skin is too acid and too arid for some species. The constant shedding of the surface skin layers further hinders the establishment of invaders. The most interesting defense mechanism, however, results from the metabolic activities of the resident flora. Unsaturated fatty acids, an important component of the lipids in sebum collected from the skin surface, inhibit the growth of several bacterial and fungal cutaneous pathogens. These acids are a metabolic product of certain gram-positive members of the cutaneous community, which break down the more complex lipids in freshly secreted sebum.

1. The primary purpose of the passage is to

A. Offer an analysis of metabolic processes

B. detail the ways in which bacteria and fungi can be- inhibited

C. Describe mechanisms by which the skin protects itself against pathogens

D. Analyze the methods whereby biological systems maintain the status quo

E. Provide a specific example of the skin’s basic defenses against pathogens

2. The “resident flora” refers to

A. “Unsaturated fatty acids”

B. “sebum collected from the skin surface”

C. “bacterial and fungal cutaneous pathogens”

D. “certain gram-positive members of the cutaneous community”

E. “more complex lipids”