OG-12-68

Passage 12

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

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

effects that they are not very useful in artificially

controlling the growth of crops. Auxin, for instance,

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

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

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

messengers from the cell wall.

68.The passage suggests that the place of hypotha-

lamic hormones in the hormonal hierarchies of

animals is similara to the place of

which of the followeing in plants?

(A) Plant cell walls

(B)The complement of genes in each plant cell

(C)A subsetof a plant cell'sgene complement

(D)The five major hormones

(E)The oligosaccharins

The best answer is D.Acording to the passage ,"The pleiotropy ofthe five well-studied plant hormones is somewhat analogous to that ofcertain hormones in animals"(lines 24-26).The example given involves certain hypothalamic hormones that "stimulate the anterir love of the pituitary gland to synthesize and release many different hormones from the adrenal cortex"(lines27-30)……

请教：题目问的是 hypothalamic hormones 的place,为什么回答是D,难道是hormones 在The five major hormones里，请大虾们解释一下

在动植物不同的激素体系中，hypothalamic hormones所处的级别和The five major hormones所处的级别相当。这是文章后两段的重点内容。

还是没搞懂，难道这里的place时表示级别吗？

能不能麻烦你将题干翻译一下，谢谢！

The passage suggests that the place of hypothaamic hormones in the hormonal hierarchies of animals is similara to the place of which of the followeing in plants?

本文表明，在动物荷尔蒙层级中，H荷尔蒙所处的地位，类似于植物层级的那种物质的地位？

好像终于懂了，谢谢王NN

你能不能再帮忙解释我写得以下几个问题

http://forum.chasedream.com/dispbbs.asp?BoardID=25&ID=47972&replyID=&skin=0

我暂时没有og的解释，所以暂时无法回答你的第1问。建议你再认真看看解释。我的大致想法是因为靠老办法探矿不行了，所以要新的理论来指导才可以。

第2问，我想我已经把我想说的说完了。请你再仔细把文章脉络理一下，

王nn,不好意思，才看到你的回帖，我已在那个链接里编辑过了，把OG的解释放上去了，请你看看，谢谢