Solar ponds are bodies of water in which circulation is incomplete and

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.

Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area

OA - C

Thank you for your explanation. I was stuck btw C & D.

Believe you chose C, not D.

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. "

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

7 min 8 seconds - A A D B (one incorrect) - Expert help needed why 4th is C.

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

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 ?

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

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.

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.