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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 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 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.# ^5 g; ]8 c) w) ~8 o# @" {
25. The passage contains information that would answer which of the following questions about the carbon cycle?
0 T1 l; e+ B& g1 Y/ I Ⅰ What are some of the compounds that are broken down in the carbon cycle?
: x7 a: E# @' _; i% p6 @4 s Ⅱ Why are some compounds that are involved in the carbon cycle less reactive than others?
9 S: j0 x+ i- M8 s; j$ C6 Z4 m Ⅲ What role do bacteria and fungi play in the carbon cycle?3 ^+ U) A! {: o% g. }+ b/ p
(A) Ⅰ only
- r- d, `% O, Y0 _ F0 L( H (B) Ⅱ only- e* y" ]/ K. [
(C) Ⅲ only2 H- Z; n% ~7 U
(D) Ⅰand Ⅱ only. H# x. O% }6 S) R( k" \: S
(E) Ⅰand Ⅲ only6 C: O$ C' R# P3 V! M. S" r
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?
& k T$ C3 C+ i( H! S5 ` (A) Most of the polymers and organic compounds found in the plant kingdom are chemically unstable.* p7 `6 o" w$ A
(B) The synthesis of some organic material deprives life processes of an energy source.$ y" q! x; H4 w4 X& D; C
(C) Decomposition permits the recycling of carbon that would otherwise be fixed in certain substances.
8 U; W) b8 [! X6 N7 e (D) Many organisms cannot use plants as a source of food, but can feed on bacteria and fungi.2 Y1 z) o. H+ s$ P
(E) Bacteria and fungi could not survive if some carbon compounds were not degraded.
% \, q. y6 \" X7 c1 v# X+ p- t 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?- g. D% n8 h( b' y' G% t+ }
(A) Both aerobes and anaerobes provide sources of energy through the decomposition of organic material.
/ U$ ]1 m0 ?5 \6 Q2 b6 u& M (B) Most compounds containing carbon are unavailable as energy sources except to some bacteria and fungi.
3 M' `( c% i t2 q9 q i7 I# W, X (C) Bacteria and fungi break down inert material in ways that do not involve oxidation.
) y- ~+ T2 D X5 v& J7 ? (D) Many compounds remain inert, even in the presence of bacteria and fungi.3 x) v* U# D% d* T- i4 Y0 y
(E) Bacteria and fungi assist in the synthesis of many organic compounds.3 @ ]+ k0 O4 ?# _8 F2 ?
28. SLUR:
' i% {9 G! B! }& |2 l6 [' N' T (A) avoid completely
( X3 V/ P [) y3 P4 E* |; }7 ~7 ^ (B) pronounce clearly
2 n$ b" {3 N8 C* ]8 q1 ?( B (C) oppose vigorously. g0 y$ F: U1 a. K3 L
(D) insist emphatically% X1 s$ |0 n! O5 [
(E) state repeatedly |
发表于 2012-8-15 12:40:43
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