GMAT阅读解析 by 申友Alice.docx

GMAT阅读解析 by 申友Alice 专业GMAT与托福保分机构 每周一篇 By 申友Alice老师 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? / (提出现象一组基因中产生的细胞形成不同的根茎叶结构。) 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 plants have now identified a new class of regulatory molecules called oligosaccharins. / (解释现象，只有一部分基因通过五大荷尔蒙和OL物质被表达出来。) / Unlikethe 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. / (五大荷尔蒙与OL物质对比，具有多效性、不专一性。) 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 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 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 from the adrenal cortex. / (植物中五大荷尔蒙的多效性和动物相似。) 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.(注意第一次出现hierarchy, 与下段开头照应。) / Such a hierarchy may also exist in plants. / (分级系统也出现在植物中。) 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, 专业GMAT与托福保分机构 more specific chemical messengers from the cell wall. / 逻辑简图： 文章属于自然科学类题材，写作结构为现象解释型。 第一段： 第一层：提出现象，一组相同的基因产生出的细胞形成不同的组织结构，如根茎叶。 第二层：解释现象，因为只有一部分的基因被表达了，并且是通过五大荷尔蒙和OL物质表达的。 第二段： 第一层：五大荷尔蒙与OL物质不同，具有多效性。 第二层：五大荷尔蒙因为具有多效性，而在控制植物生长方面不是很有效。 第三段： 第一层：五大荷尔蒙在植物中的多效性和动物中相似。 第二层：五大荷尔蒙的专一性体现在动物的目标器官中。 第四段： 第一层：分级系统也出现在植物中。 第二层：植物中的分级系统表现为荷尔蒙释放酶，酶释放OL物质。 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 错误表述 (B) each hormone has various effects on plants 同义转换，正确 (C) none of the hormones can function without the others 新说法 (D) each hormone has different effects on different kinds of plants 新说法 (E) each hormone works on only a small subset of a cells genes at any particular time 段落定位混淆 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 cells gene complement (D) The five major hormones (E) The oligosaccharins 3. The passage suggests that which of the following is a function likely to be performed by an oligosaccharin? ；第二段；第四段） (A) To stimulate a particular plant cell to become part of a plants root system 对应第一段的信息 专业GMAT与托福保分机构 (B) To stimulate the walls of a particular cell to produce other oligosaccharins 新说法 (C) To activate enzymes that release specific chemical messengers from plant cell walls. 错误表述 (D) To duplicate the gene complement in a particular plant cell. 新说法 (E) To produce multiple effects on a particular subsystem of plant cells. 错误表述 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. 新说法 (B) way in which hormones are produced by plants. 新说法 (C) hierarchical nature of the functioning of plant hormones. 段落定位混淆 (D) differences among the best-known plant hormones. 新说法 (E) concept of pleiotropy as it is exhibited by plant hormones. 例子前的总结句 5. According to the passage, which of the following best describes a function performed by oligosaccharins? ；第二段；第四段） (A) Regulating the daily functioning of a plants cells 新说法 (B) Interacting with one another to produce different chemicals 新说法 (C) Releasing specific chemical messengers from a plants cell walls 错误表述 (D) Producing the hormones that cause plant cells to differentiate to perform different functions 错误表述 (E) Influencing the development of a plants cells by controlling the expression of the cells genes 对应第一段信息 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 新说法 (B) pinpoint functions of other plant hormones 新说法 (C) artificially control specific aspects of the development of crops 对应第二段的信息 (D) alter the complement of genes in the cells of plants 新说法 (E) alter the effects of the five major hormones on plant development 新说法