历年GRE考试真题精选系列十

会计考友 · 发表于 2012-8-15 12:45:20

The whole biosphere, like the individual organisms
that live inside it, exists in a chemically dynamic states.
In this homeostatic system, a great number of organic
compounds are synthesized, transformed, and decom-
posed continuously; together, these processes consti-
tute 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, ter-
penes, and fiavonoids, 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.

25. The passage contains information that would
answer which of the following questions about
the carbon cycle?
Ⅰ What are some of the compounds that
   are broken down in the carbon cycle?
Ⅱ Why are some compounds that are
   involved in the carbon cycle less reactive
   than others?
Ⅲ What role do bacteria and fungi play in
   the carbon cycle?
(A) Ⅰ only
(B) Ⅱ only
(C) Ⅲ only
(D) Ⅰand Ⅱ only
(E) Ⅰand Ⅲ only

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 com-
   pounds 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.

27. The author’s contention about the importance
of bacteria and fungi in the production of
energy for life processes would be most clearly
strengthened if which of the following were
found to be true?
(A) Both aerobes and anaerobes provide
   sources of energy through the decom-
   position of organic material.
(B) Most compounds containing carbon are
   unavailable as energy sources except to
   some bacteria and fungi.
(C) Bacteria and fungi break down inert
   material in ways that do not involve
   oxidation.
(D) Many compounds remain inert, even in the
   presence of bacteria and fungi.
(E) Bacteria and fungi assist in the synthesis of
   many organic compounds.
25.E 26.C 27.B

		自动登录	找回密码
密码			立即注册

[GRE真题] 历年GRE考试真题精选系列十

浏览过的版块