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# GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati

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GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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Updated on: 01 May 2018, 16:43
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Passage-23 GMATPrep RCs-Collection (Main article)

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.
1.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

2. It can be inferred from the passage that which of the following is true about the salinity and temperatures of the highest and lowest water layers in a typical solar pond?

(A) The bottom layer is both highly saline and quite hot, while the top layer is less saline and cooler.
(B) The two layers have similar salinity levels, but the bottom layer is hotter than the top.
(C) There is no way to predict the salinity and temperature of the different water layers in different solar ponds.
(D) The bottom layer is less saline and quite hot, while the top layer is more saline and cooler.
(E) The top layer has both higher salinity and higher temperatures than the bottom layer.

3. According to the passage, the growth of algae was considered a threat to the success of the artificial pond near the Dead Sea because the algae

(A) produce excess oxygen that lowers the water temperature in the pond
(B) restrict the circulation of water within the pond
(C) enable heat to escape through the upper level of the pond
(D) prevent light from penetrating to the lowest levels of the pond
(E) prevent accurate measurement of the heat collected in the pond

4. 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.

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Originally posted by PiyushK on 12 Aug 2014, 08:32.
Last edited by hazelnut on 01 May 2018, 16:43, edited 3 times in total.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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Updated on: 17 Jul 2015, 08:15
3

Time taken 7 mins

1.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

2. It can be inferred from the passage that which of the following is true about the salinity and temperatures of the highest and lowest water layers in a typical solar pond?
A. The bottom layer is both highly saline and quite hot, while the top layer is less saline and cooler.

3. According to the passage, the growth of algae was considered a threat to the success of the artificial pond near the Dead Sea because the algae
D. prevent light from penetrating to the lowest levels of the pond

4. 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?
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.

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

Argument can be weaken in following way by proving that:
1) the experiment did pollute the water.
2) The experiment is not as effective as it is claimed.
etc.

C,E seems to be the only relevant options.

Option C:
Quote:
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.
This means that new factor introduced in C can pollute/contaminate the DS.

Option E: The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.
Quote:
Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area
>>Strengthen.

Originally posted by JarvisR on 13 Aug 2014, 20:44.
Last edited by JarvisR on 17 Jul 2015, 08:15, edited 3 times in total.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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20 Aug 2014, 11:16
JarvisR wrote:

Time taken 8:35 mins
Request help/discussion on Q4 as rest of the Qs are quite straightforward.

1.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

2. It can be inferred from the passage that which of the following is true about the salinity and temperatures of the highest and lowest water layers in a typical solar pond?
A. The bottom layer is both highly saline and quite hot, while the top layer is less saline and cooler.

3. According to the passage, the growth of algae was considered a threat to the success of the artificial pond near the Dead Sea because the algae
D. prevent light from penetrating to the lowest levels of the pond

4. 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?
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.

Conclusion:
This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.
Argument can be weaken in following way by proving that:
1) algae were not killed due to this experiment but by some other mean.
2) the experiment did pollute the water.
3)The experiment is not as effective as it is claimed.
etc.

C,D,E seems to be relevant compared to other options:

Though C & D introduce new factor that killed the algae but in both the options it was the experiment that introduced the factor.So in a way the experiment does control the algae.

Option E:
The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.
It actually strengthens the conclusion."Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area. "

My take on Q4.
If in reality the micro-organisms from the water which was used to dilute the pond killed algae, then we have those micro-organisms in the pond water floating now which again may hinder the process , hence this can not be called as "cleanest technology".
Guess, thats what weakens the author's conclusion.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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04 Sep 2014, 09:44
Time taken - 07mins 45 sec

1.A
2.A
3.D
4.C

Q4 - Experiment concluded that the algae died because of the shock that resulted from increasing the salinity and then introducing freshwater.
Option C perfectly weakens - It states that algae did not die of the shock but because the FW used contained microorganisms that killed the algae.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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28 Jun 2015, 20:34
1A 2A 3D 4B( One incorrect)

4 minutes 11 seconds

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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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28 Jun 2015, 20:38
Why is B incorrect ? If The lateral motility of the algae cells that sank to the bottom of the pond was not impaired then the experiment is not successful .

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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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23 Aug 2015, 04:41
manishkhare wrote:
Why is B incorrect ? If The lateral motility of the algae cells that sank to the bottom of the pond was not impaired then the experiment is not successful .

Regards,
Manish Khare

Even if lateral motility was not impaired, the algae would die of the heat(Since algae can only move laterally, it would die as temperatures are high all along the bottom layer)
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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15 Aug 2016, 09:20
manishkhare wrote:
Why is B incorrect ? If The lateral motility of the algae cells that sank to the bottom of the pond was not impaired then the experiment is not successful .

Regards,
Manish Khare

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

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

We have to find the ways that using this technology will actually cause more contamination.

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

what if that water used for is itself contaminated. Then conclusion is no longer valid.

The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.

I don't think "motility" is playing a larger role. Even if their motility is intact - this will occur - 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.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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22 Aug 2016, 05:56
Easy passage . Took 6 mins 20 seconds , including 2 mins 30 seconds to read .
-The author does not provide an opinion
- The author talks about Solar Ponds and how algae affect them and potential ways to stop algae from affecting solar ponds

1.
The author clearly describes 2 ways of solving a problem and hence option (A) is the best answer.

2."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."

3."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."

4.
If we were to establish that the reduction in algae levels was not caused by the decrease in mobility, volume etc but instead by an other cause, the argument would be sufficiently weakened. Hence option (C) which provides that alternate cause is the right answer.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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30 Oct 2016, 00:24
Time Taken : 6 Mins. All Correct. Easy Passage.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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25 Mar 2017, 05:08
7 min 8 seconds - A A D B (one incorrect) - Expert help needed why 4th is C.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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24 Jul 2017, 11:01
Nightmare007 wrote:
7 min 8 seconds - A A D B (one incorrect) - Expert help needed why 4th is C.

Hello Nightmare007,

Would like to share my opinion here.

Are you thinking that the algae are anyways getting killed and hence there should not be any impact on the conclusion - 'This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.' ? If so, then I may be of some help here.

My take on C would involve focusing on the first word of the conclusion 'This'. The conclusion is holding the mentioned method responsible for the cleaning action. Whereas, option C holds another factor of some alien microorganism responsible for the killing action. This is clearly attacking the conclusion and hence weakening it directly.

Regards.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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02 Aug 2017, 04:42
manishkhare wrote:
Why is B incorrect ? If The lateral motility of the algae cells that sank to the bottom of the pond was not impaired then the experiment is not successful .

Regards,
Manish Khare

The passage says that: The addition of water to the solar pond caused salinity change and this change distorted the algae. And when the algae settled at the bottom, high temp killed them.

Premise --> Conclusion
Sudden salinity change (by addition of water to solar pond) --> Lead to reduction in algae

Assumption :
1. The water was not hot enough to distort/kill the algae.
2. The water did not have organisms that killed the algae.

Weakener Answer: We need to ensure that the reason for reduction in algae population was NOT due to salinity change

Negating the Assumption No2, the conclusion breaks down. Hence the weakener.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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09 Sep 2017, 07:24
For Question 4, can someone explain why option D is wrong?
The author states that the change in salinity eventually killed the algae. Option D says that the rapid change in pressure did.... Isn't this option weakening the validity of the conclusion ?
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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Updated on: 18 Sep 2017, 10:32
1
pra1785 wrote:
For Question 4, can someone explain why option D is wrong?
The author states that the change in salinity eventually killed the algae. Option D says that the rapid change in pressure did.... Isn't this option weakening the validity of the conclusion ?

Hi I can help

Here is the para in which experiment is described

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.

Here the conclusion is that the introduction of saline water and evaporation resulted in the increase in salinity which in turn affected algae .
But if the distilled water contained micro organisms that killed algae then the conclusion is weakened as the reason for the death of algae is other than what the author had cited
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Originally posted by arvind910619 on 09 Sep 2017, 12:31.
Last edited by arvind910619 on 18 Sep 2017, 10:32, edited 1 time in total.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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17 Sep 2017, 19:32
1
6:35 mins, all correct.
About question 4, even I first marked B but after carefully comparing options b and c, it was obvious that only C could be the answer.
This is a typical weakener question. We have the argument with premises and conclusion. The conclusion is derived from the premise.
What if we introduced a reason that would render the premise inefficient/incorrect? The same has happened here. By mentioning that
algae were killed due to some reason other the one mentioned in the argument, we validate our point. Hence the C.

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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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05 Oct 2017, 06:00
5 MIN 7 SEC. All correct. Relatively easy passage. I wish GMAC give this kind of passage in exam as well
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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22 Oct 2017, 03:32
manishkhare wrote:
Why is B incorrect ? If The lateral motility of the algae cells that sank to the bottom of the pond was not impaired then the experiment is not successful .

Regards,
Manish Khare

The Experiment would not be unsuccessful, because motility of algae cells "SANK TO THE BOTTOM", and hence would not create obstacles for the light in water coming from top to bottom.

Posted from my mobile device
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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10 Nov 2017, 18:09
arvind910619 wrote:
pra1785 wrote:
For Question 4, can someone explain why option D is wrong?
The author states that the change in salinity eventually killed the algae. Option D says that the rapid change in pressure did.... Isn't this option weakening the validity of the conclusion ?

Hi I can help

Here is the para in which experiment is described

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.

Here the conclusion is that the introduction of saline water and evaporation resulted in the increase in salinity which in turn affected algae .
But if the distilled water contained micro organisms that killed algae then the conclusion is weakened as the reason for the death of algae is other than what the author had cited

In this case, even D is correct since it provides an alternate explanation of the behavior (algae killing).

D. The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.
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Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati  [#permalink]

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28 Feb 2018, 16:21
sevenplusplus wrote:
arvind910619 wrote:
pra1785 wrote:
For Question 4, can someone explain why option D is wrong?
The author states that the change in salinity eventually killed the algae. Option D says that the rapid change in pressure did.... Isn't this option weakening the validity of the conclusion ?

Hi I can help

Here is the para in which experiment is described

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.

Here the conclusion is that the introduction of saline water and evaporation resulted in the increase in salinity which in turn affected algae .
But if the distilled water contained micro organisms that killed algae then the conclusion is weakened as the reason for the death of algae is other than what the author had cited

In this case, even D is correct since it provides an alternate explanation of the behavior (algae killing).

D. The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.

IMO the conclusion from the final paragraph is that the method provide clean solution to algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.

Option D stated that it's killed by pressure rather than the heat, but it doesn't affect the fact that they're all killed and in a clean way. In fact it doesn't really matter how algae die, the important thing is that they DID die (one way or another), thus this option didn't weaken the conclusion at all
Re: GMATPREP ChallengeQ-Solar ponds are bodies of water in which circulati   [#permalink] 28 Feb 2018, 16:21

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