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

Hi GMAT0010,

My take on Question 4:

The conclusion derived from the experiment is : "This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.", C could undermine the conclusion in a sense that addition of microorganisms was what killed the algae and not the process used in the experiment, thus undermining the conclusion of the experiment.

Option D is indirectly mentioned in the passage as: 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.", implying that the algae cells sank to the bottom due the rapid change in pressure.

Let me know if this helps.
Thanks.

Time taken 5 mins, Can anyone please state the difficulty of these questions? Because I dont think its a 700 level passage.

Option B is tricky here.
If you don't know meaning of motility, you can consider as mobility.
Now option B says "The lateral motility of the algae cells that sank to the bottom of the pond was not impaired."
Ok so algae cells moved laterally to save itself.
Algae can move anywhere laterally,temperature will still be high enough to destroy algae.
Remember temperature vary with depth only.

Option C is correct as we have another reason that killed algae. hence conclusion drawn from experiment is undermined.

got 4th one wrong. Marked B in 1st attempt.
Now realized such a mistake could be avoided.

From the results, it shows 41% of people marked B.
It seems GMAT is well aware of mistakes that students can make.

My timing is miserable even though I could answer all of them correct.

Reading and Question 1 - : 6:15 mins
Question 2 - 0:14 mins
Question 3 - 0: 38 mins
Question 4 - 2:11 mins

Any reading strategy is appreciated!!

GMATNinja KarishmaB
Could you please help explain question 4?
I answered B because I thought that if the algae cells were not impaired when they sank to the bottom of the pond, such method would not be effective in controlling nuisance algae.

Answer B says the 'lateral motility' of the cells that sank was not impaired, not that the cells weren't damaged at the bottom. 'Lateral motility' is basically 'side to side movement,' which is not relevant to the discussion here.

Answer C is right, though I admit I'm not fully on board with the 'why.' The best I can do is that the presence of microorganisms might contaminate the water in the detrimental way discussed in the previous paragraph.

AndrewN,

Could you share your views on Question 4? I was split between (C) and (D), and neither made much sense to me. I chose (D) eventually. Seems like GMAC took a good leap of assumption in qualifying the option (C) as the correct choice here.

What are your thoughts?

QUESTION FOUR

Hello, PyjamaScientist. I imagine this passage comes from one of the paid exams. In any case, I have never seen this question set before. I am not sure if anyone else has written on question 4 above. If so, I mean no disrespect. I just want to write my own analysis and explain what led me to select the correct answer in 1:12. I approached the question more like it came from CR, and since it referred to the last paragraph only, I made that my passage.


If we want to undermine the validity of the conclusions drawn from the experiment, it is vital that we understand just what conclusions were drawn. The last paragraph of the passage:


The conclusions can be found, rather conveniently, in the final line. The method used in the experiment allows for effective control of nuisance algae. This is the first conclusion. Then, we get a second conclusion. The method also [leaves] solar ponds as one of the cleanest technologies providing energy for human use. The method itself is the only common element to the two conclusions. But if nuisance algae muddy up the waters, so to speak, then there is a relationship between getting rid of these algae and cleaning up the solar ponds. If we understand these conclusions, then the answer choices ought to be easier to navigate.


The important part is that the algae cells... were destroyed, not the time lag. The conclusions are not based on how quickly the algae were destroyed, so we cannot make heads or tails of this twenty-four-hour turnaround time. This should prove an easy elimination.


Nothing goes against the passage here, which tells us that the algae suffered impairment to motility: impairment means diminishment, not a complete breakdown. Furthermore, the sentence following the one that mentions motility informs us that the algae cells' buoyancy [was] adversely affected, so they sank and were destroyed. Thus, the conclusions are based on vertical motility, if we want to think in such terms. What the algae cells do from side to side makes no difference to the conclusions. If the algae sink, they are destroyed, even if they writhe in agony from side to side on the pond floor. We need to keep looking for a weakener.


Stop the press: if some unacknowledged factor [killed the] algae, then the conclusions based on the experiment may be premature. In other words, the intermediate conclusion that this shock reduced the cells' ability to regulate the movement of water through their membranes may not be accurate, because the saline-to-freshwater environmental change, in and of itself, would not explain the experimental results. Simply stated, the shock-to-the-system conclusion could be completely inaccurate if microorganisms that kill algae came in with the freshwater and went to work. Regarding the method used in the experiment, then, perhaps increasing the salinity of the solar ponds was a waste of time and resources. Only the addition of freshwater laden with the microorganisms might be necessary to kill the algae.


This seems similar to the previous answer choice—something else killed the algae—so what makes this option incorrect? Look at the line in question: 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. Now, my interpretation could admittedly be limited in scope, since I read just the last paragraph. (I wanted to save the passage and other questions for when I might encounter them in my own practice tests.) However, I do not see the line from the passage as necessarily implicating the temperature of the hot waters of the storage layer in killing the algae; I see the line as two separately reported pieces of information: 1) the algae sink to a particular level known as the storage layer, where the water is hot; 2) the algae were destroyed. Based on the earlier information in the paragraph, it seems to me as though the algae were already on their way out, sinking as they were. What exactly may finish them off within the hot waters of the storage layer does not affect the conclusions. The algae still sink to that layer and are destroyed. That is the major difference to my eye between this answer choice and (C) above.


If this information ties into something mentioned earlier in the passage, it was lost on me, since, again, I read only the final paragraph. In any case, the transparency of the water has no bearing on the experiment and thus does not concern us.

Perhaps the question makes more sense now, at least through the lens of confining all information about the passage to the last paragraph. Thank you for thinking to ask.

- Andrew

I have a problem with Q4
Answer C) suggests that alternative explanation for algae gotten killed is 'microorganisms from the added water', which in effect weakens the premise for mechanism of killing; but if this is acceptable then so is D) that the killing 'was due to pressure changes', which is another alternative explanation to the intermediate conclusion;

Whereas answer B) actually suggests that the lateral motility was not affected, meaning if B is true, then the algae is alive, which means it is NOT 'destroyed' as described in the passage (and they can, in turn, replicate themselves and adapt to the hotter environment, preserving their vertical motility and eventually float upwards, but we didn't need to know that).

Would really appreciate it if experts could chime in!

Can someone please explain what the difference is between option A and option E in Question Number 2.
Thanks

The tag is wrong or GMAC tagged it incorrectly. It is not a 700 level

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

yes correct. We have a way of successfully making the algae unharmful

(B) explain the mechanisms by which solar heat may be converted into energy

off totally

(C) detail the processes by which algae cells colonize highly saline bodies of water

Not the argument discussed

(D) report the results of an experiment designed to clean contaminated bodies of water..

not really . we need to clean the body of water to produce energy

(E) describe the unique properties of a solar pond on the edge of the Dead Sea

Maybe just partially this but not the ppoin

Notice how this level of the answer can be addressed even without reading the passage AT ALL. Just reading this first sentence in the 3rd part

A recent experiment has supplied a more promising method for controlling the algae.


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.
Correct A bit tricky. the key is in this sentence and relative word


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.

encounter means the top layer was cooler than the bottom layer.

(B) The two layers have similar salinity levels, but the bottom layer is hotter than the top.

Not sure where in the passage is stated that top and bottom are similar in salinity. I went A because was more cogent for me. BUT B in my opinion has some grey area to discuss

(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

The easiest of the bill. D is 3 seconds


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.

not this

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

not this

(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae.

yes and we do know from those sentence 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.

I know that the conclusion is stated in the third part but essentially we want a way to produce clean energy, kill the algae, AND keep the pond without chemicals

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

not this

(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.

Not that. maybe is the contrary

I hope this helps

This is a PLANNING argument.
The question at hand is as follows:
If we follow the given method, will algae be controlled?

B: The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.
Here, the answer is YES, since any horizontal movement by the algae cells will not protect them from the hot waters of the storage layer when they are forced to the bottom of the pond.

D: The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.
Here, the answer is also YES, since the rapid change in pressure will kill the algae cells when they are forced to the bottom of the pond.

C: The water with which the artificial solar pond was diluted contained microorganisms that kill algae.
Only here is the answer NO, since the given method does NOT suggest the use of water with these killer microorganisms.

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.


Conclusion from the experiment: "This method allows for effective control.....as one of the cleanest technologies providing energy for human use."

The question requires something that will undermine the conclusion. The conclusion mentions the proposed method would render the ponds to be the "cleanest technologies providing energy for human use".

Option C states that the water used for dilution contained microorganisms. Regarding algicide usage, the author mentions in paragraph 3, that "Extensive use of chemicals in ...would lead to such contamination of the Dead Sea". Hence, we can infer this method may not render solar pond to be the "cleanest technologies providing energy for human use".

Answer: C

For question 1 - option D is wrong as we are not talking about some experiment used in general designed to clean the bodies of water; P4 talks about an experiment designed to clean the Solar ponds to produce energy. Option A is correct; as the passage's last sentence says, "providing energy for human use" means energy source. - correct.