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 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, cytokinin, ethylene, and gibberellin, studies of planrts have now identified a new class of regulatory molecules called oligosaccharins.
第一步: 记得主语cell ，看到plant和genes。
第二步：Point 来了，how can these differentiate and form stuctures as different as roots, stems, leaves, and fruits?
第三步: 语言现象，解释前面的问题，The answer is ......
第四步：语言现象，this is accomplised by a complex system
第五步：继续解释 five major hormones :auxin, abscisic acid, cytokinin, ethylene, gibberellin
读完这一段要明白 cells 和 genes，form structures ， systems， chemical messngers， hormones , molecules ，olligosaccharins 之间的关联
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 have 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 the plant to develop a vascular system, to form lateral roots, and to produce ethylene.
第一步：请记得 plant hormones are pleiotropic; 如果pleiotropic看不懂，没关系，看后面的that is 语言信号
第二步：明白后面的Five 是指前面的 Five hormones
第三步：看到了auxin的举例，举例一般后文都会 in order to的题目。
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 lobe of the pituitary gland to synthesize and release many different hormones, one of which stimulates the release of 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.
第一步：记得 analogous to that of hormones in animals， 引出主题
第二步：for example，知道肯定是指 animals，后面又紧紧跟随了 target organs；
Such a hierarchy may also exist in plants. Oligosaccharins are fragments of the cell wall released by 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.
第一步：Point 来了， hierarachy exist in plants
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 hormones 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 (E) each hormone works on only a small subset of a cell’s genes at any particular time
定位回原文B
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 (E) The oligosaccharins
定位回原文，最后一段话，找到主语 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 (E) To produce multiple effects on a particular subsystem of plant cells
定位回原文，第一次出现的地方，明白了specific。 A
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) Concept of pleiotropy as it is exhibited by plant hormones
定义回原文，回到第一次出现的Auxin的地方，继续看，看到了Auxin, for instance, stimulates the rate of cell elongation, causes the plant to develop a vascular system, to form lateral roots, and to produce ethylene. E
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 chemic (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) Influencing the development of a plant’s cells by controlling the expression of the cell’s genes
看到Oligosaccharins，定义回原文， Unlike the oligosaccharins, the five well-known plant hormones are pleiotropic rather than specific; 和 Such a hierarchy may also exist in plants。E
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 (E) Alter the effects of the five major hormones on plant development
看到这里方反应过来，文章的重心在Oligosaccharins， 第一段的最后一句。 C
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发表于 2014-4-9 22:07:28
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