关于OG11-21篇，OG10－12

fishlibai

关于118题，

 The passage suggests that the place ofhypothalamic hormones in the hormonal hierarchies of animals is similar to the place of which of the following in plants?

(A)Plant cell walls

(B)The complement of genes in each plant cell

(C)A subset of a plant cell's gene complement

(D)The five major hormones

(E)The oligosaccharins

答案是D。我的问题是，根据og的解释，就必须理解3，4段的差不多每一句话。我觉得我考试的时候很难做到这点，实际上这篇文章我理解起来还挺困难的，第二遍看的很慢，才算弄懂了之间的关系。

就像这题目，我自己分析，第三段汁需要看首，尾两句话，其他都可以省略看。（实际上中间的我也没打看懂）然后猜测，本段说的动物里面的那个荷尔蒙层次，大概和首句提到的多功能荷尔蒙作用是相同的。文章第三段并没有直接说，但是我觉得就是这么个意思。所以答案直接选D。我不知道我这样做题方法对不对。

因为看og的解释，要弄清楚the place ofhypothalamic hormones in the hormonal hierarchies of animals ，根据第三段是处于整个层次的高端，它再刺激其他荷尔蒙的产生。然后根据第四段，Pleiotropic hormones刺激酶活动，从而产生小o。所以植物中的Pleiotropic hormones，也就是The five major hormones也处于层次的高端。这样真的是对文章要理解非常仔细了。

然后119题：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  (应该是enzymes产生小o)
(C) To activate enzymes that release specific chemical messengers from plant cell walls （应该是pleiotropic hormones）
(D) To duplicate the gene complement in a particular plant cell （没有提到duplicate的事）
(E) To produce multiple effects on a particular subsystem of plant cells   （multiple effects是荷尔蒙的事，小o应该是specific effect）

这题用排除法，可以得到答案A。
但是并不理解答案A，看了OG解释才明白，原来第三段提到，动物里面层次最低端的荷尔蒙have specific effects on target organs all over the body .
而再植物里层次最低端的小o，也应该特别作用于某个植物organ，也就是答案中的植物的root system。

同样对这个答案的理解是建立再对文章的完全理解的基础上的，而对我来说，要花很长时间。
我像请教nn们，你们是都完全理解文章了吗？还是把握文章的逻辑架构，就能帮我做好题呢？

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.

[此贴子已经被作者于2009/7/22 3:17:42编辑过]

fishlibai

没人理，自己顶