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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 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 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 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.
这篇文章我想起了,动物胚胎那篇。 第一段,说为什么植物中的细胞基因是相同,但是有的cell就是树干,有个就是果实呢?这个是有特定细胞的中的一小步基因组成的。并且要完成这个转变,需要hormone 以及regulatory molecule来完成。 话锋一转,说发现一种新的regulatory molecules. 第二段,hormone多用是多种,多样的 第三段,hormones是有等级的。 第四段, hormone 产生酶,酶生产细胞壁上的不同Oli
错误 6
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 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
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
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 第一段
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
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 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 我有些吃不准,
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 Unlike the oligosaccharins, the five well-known plant hormones are pleiotropic
Th e passage does not explicitly state how oligosaccharins could be used, but a use can be inferred. Th e second paragraph establishes that the pleiotropic hormones are not useful in artificially controlling crop growth because of their multiple, diverse eff ects. Oligosaccharins are contrasted with the hormones because they have specific eff ects. Th us it is reasonable to infer that oligosaccharins might be used to control specific aspects of crop growth.
这个变态逻辑还真是纠结,其实还有一部原文说 5 hormone不能用来被人控制。这部分加上,这个逻辑链才成立。 不会忽视 逻辑连词,unlike, although.
7. The author discusses animal hormones primarily in order to (A) introduce the idea of a hierarchy of hormones (B) explain the effects that auxin has on plant cells (C) contrast the functioning of plant hormones and animals hormones (D) illustrate the way in which particular hormones affect animals (E) explain the distinction between hormones and regulatory molecules
All of the cells in a particular plant start out (start out: 开始, 着手) 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 (abscisic acid: [生化]脱落酸), 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 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 (pituitary gland: n.[解]脑下垂体) to synthesize and release many different hormones, one of which stimulates the release of hormones from the adrenal cortex (adrenal cortex: 肾上腺皮质). These hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle (ovarian follicle: 卵泡) 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.
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 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(B)
(E) each hormone works on only a small subset of a cell’s genes at any particular time
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(D)
(E) The 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(A)
(E) To produce multiple effects on a particular subsystem of plant cells
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)
(E) concept of pleiotropy as it is exhibited by plant hormones
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 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)
(E) Influencing the development of a plant’s cells by controlling the expression of the cells’ genes
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(C)
(E) alter the effects of the five major hormones on plant development
7.The author discusses animal hormones primarily in order to
(A) introduce the idea of a hierarchy of hormones
(B) explain the effects that auxin has on plant cells
(C) contrast the functioning of plant hormones and animals hormones
(D) illustrate the way in which particular hormones affect animals(A)
(E) explain the distinction between hormones and regulatory molecules
All of the cells in a particular plant start out (start out: 开始, 着手) 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 (abscisic acid: [生化]脱落酸), 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 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 (pituitary gland: n.[解]脑下垂体) to synthesize and release many different hormones, one of which stimulates the release of hormones from the adrenal cortex (adrenal cortex: 肾上腺皮质). These hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle (ovarian follicle: 卵泡) 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.
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 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(B)
(E) each hormone works on only a small subset of a cell’s genes at any particular time
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(D)
(E) The 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(A)
(E) To produce multiple effects on a particular subsystem of plant cells
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)
(E) concept of pleiotropy as it is exhibited by plant hormones
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 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)
(E) Influencing the development of a plant’s cells by controlling the expression of the cells’ genes
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(C)
(E) alter the effects of the five major hormones on plant development
7.The author discusses animal hormones primarily in order to
(A) introduce the idea of a hierarchy of hormones
(B) explain the effects that auxin has on plant cells
(C) contrast the functioning of plant hormones and animals hormones
(D) illustrate the way in which particular hormones affect animals(A)
(E) explain the distinction between hormones and regulatory molecules
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