Microscopic plants called algae grow inside the top layer of sea ice

Question

Microscopic plants called algae grow inside the top layer of sea ice in the Antarctic if enough sunlight reaches that layer of ice and enough seawater, which contains nutrients, reaches that layer after splashing onto the surface. Even though moderate snow cover reduces the sunlight that filters into the top layer, sea ice with moderate snow cover typically contains even more algae in the top layer than does sea ice with less snow cover.

Which of the following , if true most helps to explain the apparent discrepancy?

(A) As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow.

(B) Seawater in the Antarctic often contains higher concentrations of nutrients than does seawater in more temperate regions.

(C) As the air temperature around sea ice decreases during the winter, the likelihood decreases that snow will fall and thus add to any existing snow cover.

(D) The nutrients on which algae rely are common in seawater throughout the Antarctic.

(E) More sunlight filters through a layer of ice than through an equally thick layer of snow.

The growth of algae in the uppermost layer of Antarctic sea ice depends on accessibility to sunlight and nutrient-bearing seawater that percolates downward from the surface. The amount of sunlight penetrating the ice is limited by snow cover—yet the top layer of sea ice under moderate snow cover contains more algae than sea ice under less snow cover. Why does this occur?

According to the last choice, the more snow cover, the lower the ice sinks in the water—which allows more seawater to percolate down through the ice (this presumably can also allow sunlight to penetrate at certain times). This seems a reasonable explanation, and better than the other choices given.

The first choice compares the nutritional value of Antarctic seawater with that of other seawater, but this is irrelevant to explaining the puzzle presented.

The second choice describes a process by which snow accumulation might slow down or stop—but does not help us understand how algae under moderate snow cover have acquired both enough nutrition and enough sunlight.

Clearly neither the third nor the fourth choice is any better in this respect than the second choice.

KarishmaB · Accepted Answer

Th answer is (A) only. (E) is irrelevant.

Algae grow inside the top layer of sea ice if enough sunlight reaches and enough seawater reaches that layer after splashing onto the surface (presumably, the seat water seeps into the ice after splashing on the surface).

Moderate snow cover (on top of ice) reduces the sunlight that filters into the top ice layer
Sea ice with moderate snow cover typically contains even more algae in the top layer than does sea ice with less snow cover.

This is a paradox - Ice layer needs sunlight and sea water to grow algae. Moderate snow on top of ice layer reduces sunlight reaching it. But ice with moderate snow on top of it actually grows more algae (than ice with less snow cover). Why?

(A) As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow.

Ice with moderate snow on top of it gets more sea water and hence more nutrients. So it grows more algae. Makes sense. Apparently, the impact of more nutrients outweighs the impact of less sunlight.

(B) Seawater in the Antarctic often contains higher concentrations of nutrients than does seawater in more temperate regions.

Irrelevant. Comparison is not with any other region. It is between ice with moderate snow cover and ice with less snow cover.

(C) As the air temperature around sea ice decreases during the winter, the likelihood decreases that snow will fall and thus add to any existing snow cover.

Irrelevant.

(D) The nutrients on which algae rely are common in seawater throughout the Antarctic.

Not comparing different areas of Antarctic.

(E) More sunlight filters through a layer of ice than through an equally thick layer of snow.

The comparison is between a moderate layer of snow and a thinner layer of snow. It is not between the layer of ice and layer of snow. 
In both cases, algae grow only in top layer of ice. If the ice layer has a thicker coat of snow on top of it, it gets less sunlight. If it has a thinner layer of snow on it, it gets more sunlight. Thinner layer of snow gets more sunlight than thicker layer of snow. We have to compare these two cases only. Ice vs snow is not relevant to our discussion at all.

Answer (A)

vd · Answer

I think A is the only logical answer here, as only this option opens up the logical possibility of higher algae growth even under a high snow cover

ykaiim · Answer

OA is E. This is a GMAC teaser.

The growth of algae in the uppermost layer of Antarctic sea ice depends on accessibility to sunlight and nutrient-bearing seawater that percolates downward from the surface. The amount of sunlight penetrating the ice is limited by snow cover—yet the top layer of sea ice under moderate snow cover contains more algae than sea ice under less snow cover. Why does this occur?

According to the last choice, the more snow cover, the lower the ice sinks in the water—which allows more seawater to percolate down through the ice (this presumably can also allow sunlight to penetrate at certain times). This seems a reasonable explanation, and better than the other choices given.

The first choice compares the nutritional value of Antarctic seawater with that of other seawater, but this is irrelevant to explaining the puzzle presented.

The second choice describes a process by which snow accumulation might slow down or stop—but does not help us understand how algae under moderate snow cover have acquired both enough nutrition and enough sunlight.

Clearly neither the third nor the fourth choice is any better in this respect than the second choice.

pqhai · Answer

Hi all. I'd like to confirm OA is A.
You can see the illogical reasoning in "OA" of ykaiim. Please see the   BLUE part.   What it says is exactly a paraphrased version of A,  NOT E . 
 What A says: 
(A) As the  weight of accumulated snow forces  ice lower in the water,     more seawater  splashes onto the surface and seeps through the snow.

Also, refer to the first sentence of the stimulus:
Microscopic plants called algae grow inside the top layer of sea ice in the Antarctic if enough sunlight reaches that layer of ice and enough seawater, which contains nutrients, reaches that layer after splashing onto the surface.
 Two conditions for algae growth: 
 (1) enough sunlight
(2) enough seawater

A says exactly the second condition. Thus, A is correct.

Probably, ykaiim missed the order of option choices. (I assume in his question, A is E)

To make sure the OA, you can search this question on the web, clearly OA is A.

Hope it clears your doubt.

Cheer and enjoy the question.

ankur1901 · Answer

Please let me know if my reason is correct for why E is not correct

Paradox is :  sea ice with moderate snow cover typically contains even more algea in the top layer than does sea ice with less snow cover.  
there is comparison between moderate snow and less snow, while E represents comparison between layer of ice and thick layer of snow. Hence E cannot be the answer.
Also if there is a thick layer of ice..dont think water can ever seep into it. So algae can get nutrients only from thick ice of seawater..whenever it melts.

plumber250 · Answer

Hi Ankur,

Yes you are absolutely correct.

Basically this question is saying 2 things that are seemingly paradoxical.

1. Snow blocks light
2. But Snow covered ice has more life

So the answer needs to be something that gives a benefit to snow covered ice.

E is tempting because it seems to do that, but it actually doesn't. It doesn't explain that of 2 identical pieces of ice, the one covered with snow will have more life.

Cheers.

James

WoundedTiger · Answer

Good Question...

Note that the argument initially tells us that for  Algae to grow  we need 
*Enough Sunlight
*Enough Sea water..

Note the word to grow...
And later on the conclusion is that There is more algae when there is moderate snow cover than when there is less snow cover...
Ans Choice A says 
With Moderate snow cover ---you will have more weight on top layer of sea which will sink ice lower in the water and get more water splashed and hence more nutrients but lesser light clearly pointing that nutrients is more important than sunlight for the algae population to grow

While will less snow cover, you will have more sunlight and less water being splashed vis-a-vis moderate snow cover and hence less nutrients..

Thus Nutrients are more important ad that is why we have more algae in moderate snow cover than in less snow cover...

souvik101990 · Answer

Microscopic plants called algae grow inside the top layer of sea ice in the Antarctic if enough sunlight reaches that layer of ice and enough seawater, which contains nutrients, reaches that layer after splashing onto the surface. Even though moderate snow cover reduces the sunlight that filters into the top layer, sea ice with moderate snow cover typically contains even more algae in the top layer than does sea ice with less snow cover. Which of the following, if true, most helps to explain the apparent discrepancy?

A. As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow.

B. Seawater in the Antarctic often contains higher concentrations of nutrients than does seawater in more temperate regions.

C. As the air temperature around sea ice decreases during the winter, the likelihood decreases that snow will fall and thus add to any existing snow cover.

D. The nutrients on which algae rely are common in seawater throughout the Antarctic.

E. More sunlight filters through a layer of ice than through an equally thick layer of snow.

A. according to the problem, there are two requirements to grow algae:
(1) enough sunlight
(2) enough seawater

in the situation described in the passage, the total amount of sunlight is lower, but more algae actually grow. according to the conditions given above, the only way this could happen is if more seawater somehow gets in (since there is less sunlight, and that's the only other factor that's mentioned).
therefore, you are looking for a way in which more seawater will be admitted in the situation described.

this requirement is satisfied only by choice (a).

sleepynut · Answer

Let's light up some discussion under this question :-D

StaicyT · Answer

Let's analyze the question.
The plants need nutrients and sun to grow. 
There are more plants in the surface with more snow and less sun than in the surface with less snow cover (but enough sun and water).
The flaw here is that how sea ice with larger snow cover (more snow, less sun, enough water) effects plants to grow rather than top layer of the sea ice (enough sun and water).

A. As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow. -  doesn't explain why the plant grows better without sun, but with more nutrients 
B. Seawater in the Antarctic often contains higher concentrations of nutrients than does seawater in more temperate regions. -  out of scope 
C. As the air temperature around sea ice decreases during the winter, the likelihood decreases that snow will fall and thus add to any existing snow cover. -  out of scope 
D. The nutrients on which algae rely are common in seawater throughout the Antarctic. -  doesn't explain why the plant grows better without sun, but with more nutrients 
E. More sunlight filters through a layer of ice than through an equally thick layer of snow. -    explains why there is still enough sun for the plant to grow.

sayan640 · Answer

Hi  VeritasKarishma  or GMATNinja

Can you please tell as to which one is correct A or E ?
Also some explanations for all the options will be helpful...
Can you please throw some light ?

GMATNinja · Answer

(A) is the correct answer. To see why, let's break down the information in the passage.

The first sentence sets conditions for the growth of algae:
 
From this, we know that the algae require "enough" of both sunlight and seawater to grow. Notice that we don't know exactly how much is "enough" -- we just know that the algae requires both of these things. In addition, we know that the seawater contains nutrients.

Now, on to the paradox:
 
Somehow, the algae grow better in moderately snow-covered ice, which receives  less  sunlight than does ice with less snow on top. Remember that the algae require "enough" sunlight in order to grow -- so, the reduced amount of sunlight filtering through the snow must still be enough for the algae to grow. The answer choice that "most helps explain this apparent discrepancy" should explain why the algae grow better in the snow-covered ice.

Take a look at (A):
 
(A) tells us that the moderately snow covered ice gets splashed with more seawater than does other ice. We know from the passage that seawater is required in order for the algae to grow, and that it contains nutrients. So, the ice covered by snow still receives "enough" sunlight, and in addition is splashed by more nutrient rich sea water. This definitely resolves the apparent discrepancy. (A) is our answer.

Now look at (E):
 
This passage compares the algae in a top layer of ice with "moderate snow cover" to the algae in a top layer of ice with "less snow cover." The key difference is the amount of  snow  on the  top  layer of ice. Answer choice (E) compares a layer of ice covered by snow to a layer of ice covered by... another layer of ice? In this case, we are no longer addressing the top layer of ice, which is at the heart of the discrepancy in the passage.

In addition, answer choice (E) states that more sunlight gets through the ice than the snow -- which could lead one to believe that the algae would grow more readily under ice than under snow. This is essentially the opposite of what we need. We are trying to understand how more algae could grow under  more  snow.

For these reasons, (E) is out.

I hope that helps!

edlc313 · Answer

Microscopic plants called algae grow inside the top layer of sea ice in the Antarctic if enough sunlight reaches that layer of ice and enough seawater, which contains nutrients, reaches that layer after splashing onto the surface. Even though moderate snow cover reduces the sunlight that filters into the top layer, sea ice with moderate snow cover typically contains even more algae in the top layer than does sea ice with less snow cover. Which of the following, if true, most helps to explain the apparent discrepancy?

A. As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow.
 We know that for algae to grow, it needs sunlight and water. This question answers why more snow (which would normally inhibit algae growth) might actually  help  algae grow on the top layer of ice. The answer choice says that while it may get less sunlight, it does get more water.

E. More sunlight filters through a layer of ice than through an equally thick layer of snow.
 Algae grows on the the top layer of ice, why would more sunlight filtering  through  ice help algae grow? Algae is already on the top layer. E cannot be correct. In addition, the question asks about why algae grows when ice has more snow on top of it rather than less snow. Only A provides an explanation as to why a layer of ice with more snow on it might have more algae than a layer of ice with less snow.

VerbalBot · Answer

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Microscopic plants called algae grow inside the top layer of sea ice

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Microscopic plants called algae grow inside the top layer of sea ice

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