首页
登录
职称英语
All of the cells in a particular plant start out with the same complement of
All of the cells in a particular plant start out with the same complement of
游客
2024-01-13
5
管理
问题
All of 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 sys- tern of chemical messengers that in plants include hormones and other regulatory molecules. Five major hormones have been identified: auxin, abscisic acid, cytokinin, ethylene, and gibberel- lin. Studies of plants have now identified a new class of regulatory molecules called oligosaccharide.
Unlike the oligosaccharide, 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 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 thy- roid 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. Oligosaccharides are fragments of the cell wall released by enzymes: different enzymes release different oligosaccharides. There are indications that pleiotropic plant hormones may ac- tually function by activating the enzymes that release these other, more specific chemical messengers from the cell wall. [br] The passage suggests that, unlike the pleiotropic hormones, oligosaccharides could be used effectively to
选项
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.
答案
C
解析
文中暗示,和多向性荷尔蒙不同,低聚糖可有效地用来做什么?两者成对比关系,低聚糖所做即多向性荷尔蒙所不能做的。∴C正确,人工控制作物生长特定的特性。L22—25取非的结果。A、B、D、E皆和原文中两者的比较无关。
转载请注明原文地址:https://tihaiku.com/zcyy/3359235.html
相关试题推荐
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
Visitorstothezoousuallypitytheanimalsowingtotheirparticularemoti
随机试题
Althoughwealreadyknowagreatdealaboutinfluenza,itisdifficultfore
TECTONICS:GEOLOGY::A、diary:biographyB、weather:meteorologyC、encyclopedia
梁绿琦院长为学生读者协会题词的内容是()。A.读书好、好读书、读好书 B.多
“物质一般地就是以任何一种方式刺激我们感官的东西。”这是谁给物质所下的定义()A
低温保存红细胞最常用的保护剂是( )。A.甘油 B.糖水 C.二甲亚砜
(2020年真题)关于公路工程工程量清单作用的说法,正确的有()。A.工程
公司型基金的投资者是基金公司的股东,但无权参与基金公司的管理。()
符合中心性发绀特点的是A.经按摩局部后发绀消失 B.以唇部发绀常见 C.全身
根据施工平面图对现场设施的设计,按使用期提出施工设施用料计划,报供应部门作为(
小叶性肺炎A、纤维素性炎 B、化脓性炎 C、肉芽肿性炎 D、浆液性炎 E
最新回复
(
0
)