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All of the cells in a particular plant start out with the

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All of the cells in a particular plant start out with the [#permalink] New post 10 Dec 2011, 20:07
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.


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)Influencing the development of a plant’s cells by controlling the expression of the cells’ genes
(E)Producing the hormones that cause plant cells to differentiate to perform different functions

Please reasoning your choice, thanks
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Re: 5 hormones and oligosaccharins [#permalink] New post 14 Dec 2011, 00:01
OMG it's so confusing...i went with C unfortunately..
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Re: 5 hormones and oligosaccharins [#permalink] New post 20 Dec 2011, 17:43
5. According to the passage, which of the following best describes a function performed by oligosaccharins?

The genes in a particular kind of cell...are expressed, or turned on,...by a complex system of chemical messengers that include...regulatory molecules...called oligosaccharins. (Paragraph 1)

Reverse the reverb to get D ("Influencing the development of a plant’s cells by controlling the expression of the cells’ genes").

Oligosaccharins are regulatory molecules that are chemical messengers and that turn on or express the genes in a particular kind of cell.




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Re: All of the cells in a particular plant start out with the [#permalink] New post 08 Jul 2012, 00:55
I couldn't figure out how to answer this question. Can anyone please help me?

Question 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 the plants?

(A) Plant cell walls
(B) The complement of genes in each of plant cell
(C) A subset of a plant cell's gene complement
(D) The five major hormones
(E) The oligosaccharins
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Re: All of the cells in a particular plant start out with the [#permalink] New post 08 Jul 2012, 01:36
I finally found out the answer. This question is very complicated. It took me half an hour to crack this question.

D is the correct answer.

According to the passage:

"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.

The processes in animals and in plants could be summarized as followed:

In animals: hypothalamus --> synthesize and release many different hormones --> one hormones stimulates the release of hormones from the adrenal cortex --> effects on target organs

In plants: pleiotropic plant hormones --> enzymes --> Oligosaccharins i.e. fragments of the cell wall released by enzymes --> different enzymes release different oligosaccharins

So hypothalamus can be inferred to function as pleiotropic plant hormones do.
Re: All of the cells in a particular plant start out with the   [#permalink] 08 Jul 2012, 01:36
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