OG-12-130（求助各位高手帮忙解释一下，看了下，没人问）

elizaben

130.the passage suggests that which of the following is a funtion likely to be performed by an oligosaccharin?
A. To stimulate a particular plant cell to become part of a plant's root systom
B. To stimulate the walls of a particular cell to produce other oligosaccharins
C. To activate enzymes that release specific chemical messengers from plant cell walls
D. To duplicate the gene complement in a particular plant cell
E. To produce multiple effects on a particular subsystem of plant cells

OG的解释是 A This is the only response that gives an example of an effect on a specific aspect of plant glowth and development.

我明白文章的大意，5种hormones和一种oligosaccharin比较。前者是多效性的，后者是单一功能的。可是不太明白选项。为什么只有A是单一作用的。。。（表示我是文科生，对生物这方面的知识基本菜鸟。。。）求各位好心人指点迷津啊。。。感激不尽。。。

justabeginning

建议以后LZ问问题时把文章/或相关的段落一起贴上来

泾渭不凡

All the cells in a particular plant start out with
the same complement of genes. How then can
these cells differentiate and form structures as
different as roots, stems, leaves, and fruits? The

(5)answer is that only a small subset of the genes in a
particular kind of cell are expressed, or turned on,
at a given time. This is accomplished by a complex
system of chemical messengers that in plants
include hormones and other regulatory molecules.

(10) Five major hormones have been identified: auxin,
abscisic acid, cytokinin, ethylene, and gibberellin.
Studies of plants have now identified a new class of
regulatory molecules called oligosaccharins.
Unlike the oligosaccharins, the five well-known

(15) plant hormones are pleiotropic rather than specific;
that is, each has more than one effect on the
growth and development of plants. The five have
so many simultaneous effects that they are not
very useful in artificially controlling the growth of

(20) crops. Auxin, for instance, stimulates the rate of
cell elongation, causes shoots to grow up and roots
to grow down, and inhibits the growth of lateral
shoots. Auxin also causes the plant to develop a
vascular system, to form lateral roots, and to

(25) produce ethylene.

The pleiotropy of the five well-studied plant
hormones is somewhat analogous to that of certain
hormones in animals. For example, hormones from
the hypothalamus in the brain stimulate the anterior

(30) lobe of the pituitary gland to synthesize and release
many different hormones, one of which stimulates
the release of hormones from the adrenal cortex.
These hormones have specific effects on target
organs all over the body. One hormone stimulates

(35) the thyroid gland, for example, another the ovarian
follicle cells, and so forth. In other words, there is a
hierarchy of hormones.

Such a hierarchy may also exist in plants. Oligo-
saccharins are fragments of the cell wall released

(40) by enzymes: different enzymes release different
oligosaccharins. There are indications that pleiotropic
plant hormones may actually function by activating
the enzymes that release these other, more specific
chemical messengers from the cell wall.

130.The passage suggests that which of the following is a
function likely to be performed by an oligosaccharin?



(A)To stimulate a particular plant cell to become
part of a plant's root system

(B)To stimulate the waHs of a particular cell to
produce other oligosaccharins

(C)To activate enzymes that release specific
chemical messengers from plant cell walls

(D)To duplicate the gene complement in a particular
plant cell

(E)To produce multiple effects on a particular
subsystem of plant cells

泾渭不凡

The passage suggests that which of the following is a
function likely to be performed by an oligosaccharin?

(A)To stimulate a particular plant cell to become
part of a plant's root system

(B)To stimulate the walls of a particular cell to
produce other oligosaccharins

(0To activate enzymes that release specific
chemical messengers from plant cell walls

(D)To duplicate the gene complement in a particular
plant cell

(E)To produce multiple effects on a particular
subsystem of plant cells

Inference

Answering this question requires making an
inference based on the information in the passage.
The analogy between animal and plant hormones
describes a process that ends, in animals, with
specific effects on target organs all over the body (lines
33-34). While the pleiotropic plant hormones
have multiple effects, the oligosaccharins are
described as more specific chemical messengers (lines
43-44). It is reasonable to infer that
oligosaccharins affect a specific part of a plant's
growth.

ACorrect. This is the only response that gives
an example of an effect on a specific aspect
of plant growth and development.

BThe last paragraph explains that enzymes
release oligosaccharins. The passage provides
no evidence that oligosaccharins stimulate
the release of other oligosaccharins.

CThe pleiotropic plant hormones, not the
oligosaccharins, may activate the enzymes
(lines 41-43).

DThe passage does not discuss such
duplication.

EThe oligosaccharins, as more specific chemical
messengers, have a specific effect, not
multiple effects, on plant growth.

The correct answer is A.

elizaben

谢谢楼上~~O(∩_∩)O

elizaben

嗯(⊙_⊙)谢谢楼上的建议，下次一定注意