Solar ponds are bodies of water in which circulation is

[hmgmat]

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 answer is C.

I heard different reasons for choosing C:
1. A different cause C has the same effect -- the death of algae; hence, C undermines the conclusions.
2. The conclusions are "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use", and since the water contains microorganism, it cannot be considered "one of the cleanest technologies".

I don't quite agree with #1 because if it were the case, then D could be the answer too.

I don't quite agree with #2 either because the definition of "cleanest technologies" are relative to the cleanness of other similar technologies providing energy for human use.

[hmgmat]

rescue my post on the 4th page ;-)

[trangnhung3007]

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.

The answer is C.

I heard different reasons for choosing C:
1. A different cause C has the same effect -- the death of algae; hence, C undermines the conclusions.
2. The conclusions are "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use", and since the water contains microorganism, it cannot be considered "one of the cleanest technologies".

I don't quite agree with #1 because if it were the case, then D could be the answer too.

I don't quite agree with #2 either because the definition of "cleanest technologies" are relative to the cleanness of other similar technologies providing energy for human use.

Here's my two cents:
Premises:
- Dilute the pond by a rapid inflow of fresh water
- Algae rapidly absorbed water--> distortions of shape, increase in volume, and impairment to motility.
-->Algae's 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.

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 the algae is killed by microorganisms: Algae are dead but their buoyancy is not affected. They do not sink to the storage layer. The dead cells are still floating in the higher layer, preventing "the penetration of light to the deep storage area"
--> undermine the above conclusion.

Looking forward to hearing your opinions!

[RonPurewal]

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 answer is C.

I heard different reasons for choosing C:
1. A different cause C has the same effect -- the death of algae; hence, C undermines the conclusions.
2. The conclusions are "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use", and since the water contains microorganism, it cannot be considered "one of the cleanest technologies".

I don't quite agree with #1 because if it were the case, then D could be the answer too.

I don't quite agree with #2 either because the definition of "cleanest technologies" are relative to the cleanness of other similar technologies providing energy for human use.

The conclusion in the final paragraph states that This method allows for effective control of nuisance algae.
in other words, this paragraph is absolutely certain that the inflow method actually kills the algae, just because of the evaporation and inflow.
to weaken this conclusion, you'd have to find some other explanation for the death of the algae, unrelated to the evaporation/inflow procedure.
this is what choice (c) does. if (c) is true, then the algae may not have been killed by the procedure at all; they may have been killed by the microorganisms that were introduced.

so, wait - which answer did you think was correct instead?

[atulmangal]

I picked Op B...seems like i thought out of the league here...anyways..

First, i think the OP B means, that the lateral mobility of the Algae is not affected. Correct me here if i'm interpreting the wrong meaning.

If the meaning is correct, then, it means Algae doesn't remain on the bottom and rise up again at the surface and that means that the whole experiment fails...

Actually i thought that the question stem is asking us to pick an Option which suggests...why the complete experiment going to fail...so i was looking for an option which do the same...

[george.kourdin]

somewhat confused....

the crux of the argument is that this method = (the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water) "allows for effective control of nuisance algae", correct?

pls correct me if i am wrong, but it seems like both (C) and (D) provide alternative methods for the death of the algae. the reason why C>D is that D focuses on the algae that sank to the bottom of the pond. For that to happen, the method described in the passage (inflow causes algae to sink) has had to have worked, right? Thus, it seems somewhat incomplete and not nearly as strong of a counter-argument as (C).

If that is not the reason why C>D, can someone please explain.

thanks

[RonPurewal]

somewhat confused....

the crux of the argument is that this method = (the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water) "allows for effective control of nuisance algae", correct?

pls correct me if i am wrong, but it seems like both (C) and (D) provide alternative methods for the death of the algae. the reason why C>D is that D focuses on the algae that sank to the bottom of the pond. For that to happen, the method described in the passage (inflow causes algae to sink) has had to have worked, right? Thus, it seems somewhat incomplete and not nearly as strong of a counter-argument as (C).

If that is not the reason why C>D, can someone please explain.

thanks

(d) provides an alternative explanation, but it's still a result of the method described. i.e., the intermediate steps of the process are debated, but it's still clear that the original method is ultimately responsible for killing the algae. therefore, (d) doesn't undermine the conclusions at all.

[RonPurewal]

I picked Op B...seems like i thought out of the league here...anyways..

First, i think the OP B means, that the lateral mobility of the Algae is not affected. Correct me here if i'm interpreting the wrong meaning.

If the meaning is correct, then, it means Algae doesn't remain on the bottom and rise up again at the surface and that means that the whole experiment fails...

Actually i thought that the question stem is asking us to pick an Option which suggests...why the complete experiment going to fail...so i was looking for an option which do the same...

"lateral" means sideways, so this choice doesn't have these implications for vertical (i.e., non-lateral) motion.

[gmatwork]

Why is choice (b) wrong? Can someone please elaborate?

[RonPurewal]

Why is choice (b) wrong? Can someone please elaborate?

choice (b) is already discussed in the post above yours; if you still have questions about it, please ask a more specific question. thanks.

[supratim7]

The conclusion in the final paragraph states that This method allows for effective control of nuisance algae.
in other words, this paragraph is absolutely certain that the inflow method actually kills the algae, just because of the evaporation and inflow.

Good discussion. Looks like the key is to pinpoint the conclusion (as Ron has done here).

I consciously tried to do so but couldn't. Especially under time pressure. Ended up noting few minor points/intermediate points e.g. "dilution shock impaired motility", "poor buoyancy led to sinking", "bottom layer water heat destroyed algae", etc..

Ron, could you please illustrate briefly--how to pinpoint a conclusion within the maze of info given in a RC passage quickly. Pls throw in your usual bold-faced words of wisdom too :)

Regards | Supratim

[RonPurewal]

Ron, could you please illustrate briefly--how to pinpoint a conclusion within the maze of info given in a RC passage quickly. Pls throw in your usual bold-faced words of wisdom too :)

the only meaningful answer i have to this question is, "read the passage like an everyday person reading a newspaper, and NOT like a student reading an 'academic' passage."
if you can get yourself into that frame of mind, this problem should essentially solve itself. (same goes for strengthening/weakening problems on CR, on which you have to use a lot of real-world common sense to make inferences.)

you're not going to find a better answer than that, by the way.
if someone had a better answer, then that person would be holding a huge piece of the heretofore unsolved puzzle of "strong artificial intelligence".

[supratim7]

"read the passage like an everyday person reading a newspaper, and NOT like a student reading an 'academic' passage."
if you can get yourself into that frame of mind, this problem should essentially solve itself.

Noted Ron. Will give it a try.
Appreciate your help.

[jlucero]

Glad we can help.

[ShirleyB128]

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 answer is C.

I heard different reasons for choosing C:
1. A different cause C has the same effect -- the death of algae; hence, C undermines the conclusions.
2. The conclusions are "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use", and since the water contains microorganism, it cannot be considered "one of the cleanest technologies".

I don't quite agree with #1 because if it were the case, then D could be the answer too.

I don't quite agree with #2 either because the definition of "cleanest technologies" are relative to the cleanness of other similar technologies providing energy for human use.

Pretty strange information..Well I have been seriously considering to establish solar pond and the post details is changing my thoughts.. I will gather some more details about these ponds..