Although pathogenic organisms constantly
alight on the skin, they find it a very unfavor-
able environment and, in the absence of injury,
have great difficulty colonizing it. This "self-
(5) 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
(10)elsewhere rarely multiply on the skin. Un-
damaged 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
(15)defense mechanism, however, results from the
metabolic activities of the resident flora.
Unsaturated fatty acids, an important com-
ponent of the lipids in sebum collected from
the skin surface inhibit the growth of several bac-
(20)terial 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.
17. 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 defense against pathogens
18. The "resident flora" mentioned in line 16 refer to
(A) "Unsaturated fatty acids" (line 17)
(B) "sebum collected from the skin surface" (lines 18-19)
(C) "bacterial and fungal cutaneous pathogens" (lines 19-20)
(D) "certain gram-positive members of the cutaneous community" (lines 21-22)
(E) "more complex lipids" (line 23)
19. Among the natural defense of the skin against pathogenic organisms are all of the following EXCEPT the
(A) dryness of the skin
(B) acidity of the skin
(C) tendency of the pathogens toward homeostasis
(D) shedding of surface layers of the skin
(E) metabolic breakdown of lipids
20. The author presents her material in which of the following ways?
(A) Stating a problem and then supplying a solution
(B) Presenting a phenomenon and then analyzing reasons for it
(C) Providing information and then drawing a conclusion from it
(D) Making a general statement and then arguing by analogy
(E) Making an inference and then developing it by illustration |
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