Solar pond

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Solar pond

by atulmangal » Sun May 08, 2011 11:29 am
Solar ponds are bodies of water in which circulation is incomplete and there is a very high salt concentration that increases with depth. This vertical change in salinity serves to trap heat because concentrated brine in the lowest water level acts as a collector and storage area for solar heat, while the less saline, lighter water at the upper levels provides insulation. Heat is thus retained in the depths.

An artificial pond of this type has been constructed on the western shore of the Dead Sea in Israel in order to test its suitability as a source of low-grade heat for conversion into electricity. An immediate threat to the success of the venture was the growth of algae. Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area. Therefore, any particles of matter in the water, such as algae cells, that scatter or absorb light will interfere with the collection of heat.

One proposed method of controlling the algae was the application of an algicide. However, the Dead Sea is a closed body of water without any outlet and as such is very easily contaminated. Extensive use of chemicals in numerous future full-scale solar ponds would lead to such contamination of the Dead Sea, which now enjoys a lucrative tourist trade.

A recent experiment has supplied a more promising method for controlling the algae. To repress the algae cells' capacity for accommodating themselves to environmental changes, the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water. This shock reduced the cells' ability to regulate the movement of water through their membranes. They rapidly absorbed water, resulting in distortions of shape, increase in volume, and impairment to motility. Their buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed. This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.

Which of the following, if true, would seriously undermine the validity of the conclusions drawn from the experiment described in the last paragraph of the passage?

(A) The algae cells that sank to the bottom of the pond were destroyed only after a time lag of twenty-four hours.
(B) The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.
(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae.
(D) The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.
(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.

The primary purpose of the passage is to
(A) discuss ways of solving a problem that threatens to limit the usefulness of an energy source
(B) explain the mechanisms by which solar heat may be converted into energy
(C) detail the processes by which algae cells colonize highly saline bodies of water
(D) report the results of an experiment designed to clean contaminated bodies of water
(E) describe the unique properties of a solar pond on the edge of the Dead Sea


[spoiler]for first question i thought our goal is to suggest a way in which the Algae cells will not get destroyed. I thought that the final conclusion of the last paragraph is that Algae cells are destroyed. For this, if the lateral movement of cells is not justified...then Algae cells will not destroy because of excessive heat...m i thinking in correct direction???[/spoiler]

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by mundasingh123 » Mon May 09, 2011 2:06 am
Hi Whats the source ?
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by atulmangal » Mon May 09, 2011 6:41 am
mundasingh123 wrote:Hi Whats the source ?
Hi i wonder you always ask for the source in almost all questions, just because of curiosity, is there any specific reason for that? For record, i use only one standard resource i.e OG apart from that i have question bank which contains questions compiled from almost all the standard resources and this question is one of them. I don't know from which source this question originally belong too.

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by mundasingh123 » Mon May 09, 2011 7:48 am
atulmangal wrote:
mundasingh123 wrote:Hi Whats the source ?
Hi i wonder you always ask for the source in almost all questions, just because of curiosity, is there any specific reason for that? For record, i use only one standard resource i.e OG apart from that i have question bank which contains questions compiled from almost all the standard resources and this question is one of them. I don't know from which source this question originally belong too.
I havent taken the gmatprep or manhattan GMT Cats yet ,thats why .:)
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by vikram4689 » Mon May 09, 2011 8:14 am
IMO : C and A respectively
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by atulmangal » Mon May 09, 2011 8:21 am
vikram4689 wrote:IMO : C and A respectively
Can u justify your answer for Q-1

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by vikram4689 » Mon May 09, 2011 8:46 am
It gives entirely different reason why algae is killed and this undermines the conclusion.
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by mundasingh123 » Mon May 09, 2011 9:37 am
This is a GmatPrep , if anybody cares to know
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by atulmangal » Mon May 09, 2011 9:49 am
vikram4689 wrote:It gives entirely different reason why algae is killed and this undermines the conclusion.
why no Op D then too, it also suggests a different way to kill algae????

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by atulmangal » Mon May 09, 2011 9:50 am
mundasingh123 wrote:This is a GmatPrep , if anybody cares to know
Its horrible then, i answered this question wrong... :D

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by HSPA » Mon May 09, 2011 7:18 pm
IMO C and D
atulmangal wrote:Solar ponds are bodies of water in which circulation is incomplete and there is a very high salt concentration that increases with depth. This vertical change in salinity serves to trap heat because concentrated brine in the lowest water level acts as a collector and storage area for solar heat, while the less saline, lighter water at the upper levels provides insulation. Heat is thus retained in the depths.

An artificial pond of this type has been constructed on the western shore of the Dead Sea in Israel in order to test its suitability as a source of low-grade heat for conversion into electricity. An immediate threat to the success of the venture was the growth of algae. Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area. Therefore, any particles of matter in the water, such as algae cells, that scatter or absorb light will interfere with the collection of heat.

One proposed method of controlling the algae was the application of an algicide. However, the Dead Sea is a closed body of water without any outlet and as such is very easily contaminated. Extensive use of chemicals in numerous future full-scale solar ponds would lead to such contamination of the Dead Sea, which now enjoys a lucrative tourist trade.

A recent experiment has supplied a more promising method for controlling the algae. To repress the algae cells' capacity for accommodating themselves to environmental changes, the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water. This shock reduced the cells' ability to regulate the movement of water through their membranes. They rapidly absorbed water, resulting in distortions of shape, increase in volume, and impairment to motility. Their buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed. This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.

Which of the following, if true, would seriously undermine the validity of the conclusions drawn from the experiment described in the last paragraph of the passage?

(A) The algae cells that sank to the bottom of the pond were destroyed only after a time lag of twenty-four hours.
(B) The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.
(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae.
(D) The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.
(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.

The primary purpose of the passage is to
(A) discuss ways of solving a problem that threatens to limit the usefulness of an energy source
(B) explain the mechanisms by which solar heat may be converted into energy
(C) detail the processes by which algae cells colonize highly saline bodies of water
(D) report the results of an experiment designed to clean contaminated bodies of water
(E) describe the unique properties of a solar pond on the edge of the Dead Sea


[spoiler]for first question i thought our goal is to suggest a way in which the Algae cells will not get destroyed. I thought that the final conclusion of the last paragraph is that Algae cells are destroyed. For this, if the lateral movement of cells is not justified...then Algae cells will not destroy because of excessive heat...m i thinking in correct direction???[/spoiler]
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by LIL » Tue May 10, 2011 5:48 pm
the answer to the first question is (c)

the conclusion of the last paragraph is that the method the experiment described -- increasing salinity through evaporation, diluting the water with a rapid inflow of fresh water -- "allows for effective control of nuisance algae."

in other words, "we tried this experiment and it worked." to weaken this conclusion, we must show that this experiment may not have actually worked. answer (c) brings in another factor -- that the fresh water may have algae-killing microorganisms, and those may have actually killed the algae, instead of the experiment.

i see someone is asking why (d) is incorrect -- this is because the algae is still being killed as a result of the experiment, even if the scientists don't realize that this is the reason the algae is being killed. think about it this way -- with choice (d) you still must use the experimental method (because it causes the cells to experience the "rapid change in pressure" as they fall to the bottom of the pond). but for choice (c) you could just throw the freshwater in and the microorganisms would do their job -- in other words, no need to use the other method.

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by champmag » Wed May 18, 2011 1:03 am
B and A.

The conclusion of the last paragraph states that the method used allows for an effective control of nuisance algae while leaving the ponds clean.

Any option that saya that algae nuisance is not yet over is the one that weakens the conclusion.
Op B says that the lateral movement of algae was not impaired i.e( in my opinion) algae were still floating in water, even though they were destroyed. I think this is better attck on the conclusion than Op C. Please correct me Atul, if I am wrong.

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by [email protected] » Wed May 18, 2011 2:12 am
The main thing with Q1 is to first clarify for yourself what are you trying to weaken - what is the conclusion drawn from the experiment. This is actually not different from any regular weaken CR question - find the premises and conclusion. This is the last sentence:

"This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use. "

So there are actually two conclusions that we can weaken: that the method words, and that it's still clean (as opposed to the algicide method discounted as too messy in the third paragraph). I think that C is the right answer because it weakens the second conclusion: microorganisms that kill algae can be considered a contaminating algicide, indicating that the method, while effective, is not clean.

Call this a supporting point in addition to the comments above. At the end of the day, the answer is C because it is not A, B, D or E, i.e. b elimination.
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by [email protected] » Wed May 18, 2011 2:20 am
The answer for Q2 is A. The passage begins by telling us about solar ponds and the opportunity they present to generate elctrcity. The rest of the passage deals with the algae problem and the proposed methods for solving it. A is the answer choice that best and most comprehensively describes the various components of the passage.
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