GMAT阅读OG 13 26篇详细分析-25

　　新东方在线为大家精心整理了GMAT阅读OG 13 26篇详细分析的相关内容，分享给大家，供大家参考，希望对大家有所帮助!

　　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 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 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.

　　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.

　　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.

　　Questions 128-133 refer to the passage above.

　　128. 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

　　E. each hormone works on only a small subset of a cell's genes at any particular time

　　129. 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

　　130. 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

　　131. 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

　　132. 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. Influencing the development of a plant's cells by controlling the expression of the cells' genes

　　133. 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. alterthe effects of the five major hormones on plant development

　　题材：Biology

　　类型：描述型

　　框架：plant hormone(难)

　　主旨：植物生长素的多效性与特定性及其层次体系

　　P1:提出植物中的五种荷尔蒙和寡聚糖素;

　　P2:五种荷尔蒙和寡聚糖素的不同点和各自特点，并举例说明;

　　P3:五种荷尔蒙的特点与动物体内的荷尔蒙分泌相似;

　　P4:这种层级也可能在植物中存在。

　　又一篇生物的典型文章。理清各种术语之间的关系仍然是关键。从开头可以看出，设问句后的回答也是GMAC的重点之一。另外，本文另一个tricky之处是通过animal的类比来解释一个东西的作用，而最后一段意犹未尽，cionclusion需要读者从开头的首位照应中联想：oligosaccharins就是那改变植物成长的关键要素。

　　逻辑链：

　　1、提出问题，回答，引入5大激素

　　2、激素的特点，举例

　　3、激素的多效性和动物类似，举例，引出激素阶层

　　4、这种阶层在植物中也存在，证据

　　题目类型：128：细节信息 129：细节推断 130：细节推断 131：句子功能 132：细节信息 133：细节推断

　　解题定位(根据OG13解释)：

　　128：激素的性质，定位Line16-20

　　129：看文章的逻辑链，先介绍5大激素和其性质，然后说和动物相似，动物中的阶层在植物中存在，根据文章的专业词汇定位到第三段和第四段，其实意思就是找动物和植物的共性，就是5个激素，实在不知道共性怎么找的话，全文的中心就是描述5大激素，往这方面靠拢

　　130：问题让你找O的特性，而原文大部分是在说共性，所以要对比动物和植物的区别。定位Line43-44，O的特性是more specific chemical messengers，而激素在动物中是Line33-34，specificeffects on target organs all over the body。所以可以推出O affect a specific part of a plant's growth.

　　131：Auxin是出现在20行的，但后面紧跟一个词for instance，说明此句的作用要么是针对前一句，要么是针对此段中心句，答案是针对中心句：has more than one effect on the growth and development of plants

　　132：定位Line14-17，O的作用和5大激素是不同的，因为第二段开头来了个unlike O，所以答案往上找，定位Line5-7，选项是此句的概括。而且我觉得OG13最后一句解释说反了=。=

　　133：全文唯一一个说激素不好的地方就是：对人为控制的作物无效，定位Line17-20，而第二段又说了激素和O是不同的，所以可以推断O对人为控制是有效的。太尼玛难找了这个点=。=

　　以上就是新东方在线为大家总结的GMAT阅读OG 13 26篇详细分析的相关内容，最后预祝大家在GMAT考试中取得优异的成绩!

课程推荐》》更多