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Plant cell

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massi2884 Senior | Next Rank: 100 Posts Default Avatar
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Plant cell

Post Sun Oct 30, 2011 6:07 am
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.

Q
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

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herbalsejagat Newbie | Next Rank: 10 Posts
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Post Tue Sep 19, 2017 7:41 pm
Thank you Essay Snark!

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massi2884 Senior | Next Rank: 100 Posts Default Avatar
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Post Mon Oct 31, 2011 2:24 am
Yes, it's correct. Thanks a lot, that question wasn't easy at all.

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essaysnark Legendary Member
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Post Sun Oct 30, 2011 6:53 am
We had to attack this one purely by elimination. We think it's A.

(A) To stimulate a particular plant cell to become part of a plant’s root system We were left with this one at the end, after eliminating all the others... and when we re-read it then, it sounds feasible, so that's what we're going with!
(B) To stimulate the walls of a particular cell to produce other oligosaccharins It says that enzymes produce oligs, it doesn't say that oligs can produce other oligs, so we're disqualifying this.
(C) To activate enzymes that release specific chemical messengers from plant cell walls The oligs are the "chemical messengers" themselves so this can't be right - this sorta sounds the same as B and we've already decided that's incorrect. So ruling this one out.
(D) To duplicate the gene complement in a particular plant cell This sounds counter to the very first sentence in the passage; it says all the cells start w/ the "same complement" so why would an olig need to "duplicate" that? Nixing this too.
(E) To produce multiple effects on a particular subsystem of plant cells Can definitely cross this one out, the passage says that oligs do just one thing only.

massi2884, would love to know the OA, to see if our logic is sound!

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massi2884 Senior | Next Rank: 100 Posts Default Avatar
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Post Sun Oct 30, 2011 10:32 am
Hi, that's correct. However, my intent was posting the following question related to the same passage. Can you guys help? OG explanation is not clear to me. Thanks.

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

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essaysnark Legendary Member
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Post Sun Oct 30, 2011 10:55 am
OK let's break this one down, too. We think the answer is E.

We got this from working backwards in the first paragraph. Here's the sequence of sentences that led us to this answer:

1. "Studies of plants have now identified a new class of regulatory molecules called oligosaccharins."
So, oligs are "regulatory molecules."

2. "This is accomplished by a complex system of chemical messengers that in plants include hormones and other regulatory molecules."
Oligs are chemical messengers.

3. What is accomplished by those "chemical messengers"? The sentence before that one tells us: "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."
So, oligs turn on ("express") genes in certain cells.

It can't be D because we already established that oligs don't produce hormones, right?

And, the passage doesn't say anything about oligs interacting with each other; they are called "regulatory molecules", we're not told anything about them producing stuff. So it can't be B.

And, nothing in the passage talked about "daily function" - the whole thing was about the plant's "growth and development" - so we're ruling out A.

C is a tougher one since it's got the definition of oligs wrapped up in it. The passage says that "Oligosaccharins are fragments of the cell wall released by enzymes" -- but C mixes that up to say that that's what oligs do. So that's where that one seems wrong.

Now you've got EssaySnark's thought process all mapped out here - not sure if we're right but that's how we broke this problem down!!!

EssaySnark

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