OG 阅读第69题

剛巧路過…….

最後一句再回應文章中的重點oligosaccharin 是specific

以此concept 來做答

(A) To stimulate a particular plant cell to become part of a plant’s root system (oligosaccharin是specific ß> particular  )

(B) To stimulate the walls of a particular cell to produce other oligosaccharins（oligosaccharin 是由enzymes release 的 詳見L37）

(C) To activate enzymes that release specific chemical messengers from plant cell walls（詳見L36--37）

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

但你如何知道它是root system,而不是stem,leaves.....

文章最后一句: There are indications that pleiotropic plant hormones may actually function by activating the enzymes that release these other, more specific chemical messengers fromthe cell wall.

"these other"应该指代Oligosaccharins,"more specific chemical messengers fromthe cell wall"做Oligosaccharins的同位语.

一家之言.

以OG的解釋似乎 particular是取非這題解答的標準

另外 root system就是包含steam, leaves...等

E为什么不对啊？

你们都说specific = particular，可是每个选项都出现particular了啊！

Passage 24

All of 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 answer is that only a

(5) small subset of the genes in a particular kind of cell are

expressed, or turned on, at a given time. This is accom-

plished by a complex system of chemical messengers

that in plants include hormones and other regulatory

molecules. Five major hormones have been identified:

(10) auxin, abscisic acid, cytokinin, ethylene, and gibberel-

lin. Studies of plants have now identified a new class of

regulatory molecules called oligosaccharins.

Unlike the oligosaccharins, the five well-known plant（Q69,Q72）

hormones are pleiotropic rather than specific, that is,

(15) each has more than one effect on the growth and devel-

opment of plants. The five has so many simultaneous(Q67,Q71)

effects that they are not very useful in artificially

controlling the growth of crops. Auxin, for instance,(Q70)

stimulates the rate of cell elongation, causes shoots to

(20) 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

produce ethylene.

The pleiotropy of the five well-studied plant

(25) hormones is somewhat analogous to that of certain(Q68)

hormones in animal. For example, hormones from the

hypothalamus in the brain stimulate the anterior lobe

of the pituitary gland to synthesize and release many

different hormones, one of which stimulates the release

(30) of hormones from the adrenal cortex. These hormones

have specific effects on target organs all over the body.

One hormone stimulates the thyroid gland, for

example, another the ovarian follicle cells, and so forth.

In other words, there is a hierarchy of hormones.

(35) Such a hierarchy may also exist in plants. Oligosac-

charins are fragments of the cell wall released by

enzymes: different enzymes release different oligosac-

charins. There are indications that pleiotropic plant

hormones may actually function by activating the (Q69,Q71)

(40) enzymes that release these other, more specific chemical

messengers from the cell wall.

当然首先你应该知道oligosaccharin 的preperty,A就是它的特性的应用

应该跟particular没多大关系，我觉得应该注意的是最后一段的第一话的anology:Such a hierarchymay also exist in plant.只最后一句orientation 还不行