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.
According to the passage, which of the following best describes a function performed by oligosaccharins?
我有更好的解析 
暂无雷哥网文字解析
关键词function performed by oligosaccharins当前版本由 kisenana 更新于2015-11-05 16:03:17 感谢由 kisenana 对此题目的解答所做出的贡献。
选项A Regulating the daily functioning of a plant’s cells regulate植物细胞的daily function未提及
选项B O相互interact 产生different chemicals未提及
选项C 从cell walls释放specific chemical messengers O就是cell wall fragment
选项D Producing the hormones错误 定位到文章最后一段荷尔蒙产生作用的原理：是enzyme→H荷尔蒙→O；O不可以反过来产生H
选项E 文章第一段 H和O可以控制gene表达，正确
关键词function performed by oligosaccharins
选项A Regulating the daily functioning of a plant’s cells regulate植物细胞的daily function未提及
选项B O相互interact 产生different chemicals未提及
选项C 从cell walls释放specific chemical messengers O就是cell wall fragment
选项D Producing the hormones错误 定位到文章最后一段荷尔蒙产生作用的原理：是enzyme→H荷尔蒙→O；O不可以反过来产生H
选项E 文章第一段 H和O可以控制gene表达，正确
主要看最后一句话“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.”，所以物质关系是 PPH激活enzyme，让enzyme产生Oligo，进而达成PPH的效用，即控制基因表达、促进细胞分化。
0
0
回复
2022-12-29 11:31:33
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.
0
0
回复
2020-11-01 01:52:19
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.
0
0
回复
2018-08-24 19:07:24
C只是描述一种特殊情况
1
0
回复
2018-07-22 10:27:42
All the cells in a particular plant start out with the same complement of genes
0
0
回复
2017-08-26 13:46:05
Oligosaccharins are fragments of the cell wall released by enzymes。———————— 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.
0
0
回复
2017-01-14 11:10:52
见过夏天去非洲拍动物世界回复见过夏天去非洲拍动物世界
相信自己的对文章的判断，基于原文，做出自己认为最合适的选项，剔除自己认为有理由剔除的选项，就好。
0
0
回复
2017-01-14 11:11:40
科目：
阅读RC
来源：
精选题库
2m11s
平均耗时
36.7%
平均正确率
该题由网友e7duU提供 上传GMAT题
分享
周末、晚班滚动开班 
24+35+35+6课时 
