|
24/63
All of the cells in a particular plant start out (start out: 开始, 着手) 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 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. Five major hormones have been identified: auxin, abscisic acid (abscisic acid: [生化]脱落酸), 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 plant hormones are pleiotropic rather than specific; that is, each has more than one effect on the growth and development 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 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 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 (pituitary gland: n.[解]脑下垂体) to synthesize and release many different hormones, one of which stimulates the release of hormones from the adrenal cortex (adrenal cortex: 肾上腺皮质). These hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle (ovarian follicle: 卵泡) cells, and so forth. In other words, there is a hierarchy of hormones.
Such a hierarchy may also exist in plants. Oligosaccharins are fragments of the cell wall released 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.
1. According to the passage, the five well-known plant hormones are not useful in controlling the growth of crops because
(A) it is not known exactly what functions the hormones perform
(B) each hormone has various effects on plants
(C) none of the hormones can function without the others
(D) each hormone has different effects on different kinds of plants（B）
(E) each hormone works on only a small subset of a cell’s genes at any particular time
2. The passage suggests that the place of hypothalamic 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（D）
(E) The oligosaccharins
3. 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
(C) To activate enzymes that release specific chemical messengers from plant cell walls
(D) To duplicate the gene complement in a particular plant cell（A）
(E) To produce multiple effects on a particular subsystem of plant cells
4. The author mentions specific effects that auxin has on plant development in order to illustrate the
(A) point that some of the effects of plant hormones can be harmful
(B) way in which hormones are produced by plants
(C) hierarchical nature of the functioning of plant hormones
(D) differences among the best-known plant hormones（E）
(E) concept of pleiotropy as it is exhibited by plant hormones
5. According to the passage, which of the following best describes a function performed by oligosaccharins?
(A) Regulating the daily functioning of a plant’s cells
(B) Interacting with one another to produce different chemicals
(C) Releasing specific chemical messengers from a plant’s cell walls
(D) Producing the hormones that cause plant cells to differentiate to perform different functions（E）
(E) Influencing the development of a plant’s cells by controlling the expression of the cells’ genes
6. The passage suggests that, unlike the pleiotropic hormones, oligosaccharins could be used effectively to
(A) trace the passage of chemicals through the walls of cells
(B) pinpoint functions of other plant hormones
(C) artificially control specific aspects of the development of crops
(D) alter the complement of genes in the cells of plants（C）
(E) alter the effects of the five major hormones on plant development
7. The author discusses animal hormones primarily in order to
(A) introduce the idea of a hierarchy of hormones
(B) explain the effects that auxin has on plant cells
(C) contrast the functioning of plant hormones and animals hormones
(D) illustrate the way in which particular hormones affect animals（A）
(E) explain the distinction between hormones and regulatory molecules
这个我写的比较详细,很多地方我用了原文,没有用中文概括.我想让你明白读文章的重点.
绿字是定位点. 粉红字是解题的对应点
文章结构
结论解释型文章. Presentation类型.
第一段: plant形成由his is accomplished by a complex system of chemical messengers that in plants include hormones and other regulatory molecules(TS,主题句).
Hormones包括5个主要的…., molecules包括一个叫Oli (玉兰油呀,哈哈哈!!)的.(看到这里其实就可以猜测了,文章跑不了说5个hormones,和一个Oli.
第二段: Unlike(什么都可以不看,like, unlike, on the other hand, in the contrary, 不敢不细看,而且必定取非). 论点: 5个hormones是非specific. evidence, for instance.
第三段: 论点: P of 5个hormones is analogous to that of certain hormones in animals. Evidence. For example.
第四段: 论点: such a H may also exist in plants. 接着说明.
67. According to the passage, the five well-known plant hormones are not useful in controlling the growth of crops because: 事实题. 定位2段:
68. The passage suggests that the place of hypothalamic hormones in the hormonal hierarchies of animals is similar to the place of which of the following in plants? 细节题.根据动物定位3段.
在动物里面: Hypo>>>>(stimulate) anterior lobe of the pituitary gland (合成,释放) >>>>不同的hormones( 这些hormones是有specific效果的)
在植物里面: P hormones(include 5)>>>>(activating) enzymes>>>many Oli (这个才是specific的).
这里面比较混的是.动物的hormones是specific的. 而植物中的hormones是P的(非specific).
植物中是分子Oli specific.
看懂了这个对比关系. HYPO 对应 5 个hormones.
69. 难题: 按OG的解释,其实就是其他4个都不对, 而且A说了particular=specific对. 请妹妹自己列出其他错误
70.举例作用题. 没什么说的. For example, for instance, 都是evidence,都是用来说明论点的.二段就说了个concept of P.
71. infer题, 也挺难的, 看OG解释.我没有什么好方法.
72. Unlike,定位,取非.
这篇文章好象我第一次做的时候,只对了一两个.
[此贴子已经被作者于2004-6-11 15:17:18编辑过] | 
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2004-6-10 09:44:00
楼主
