Source: Official Guide Revised GRE 1st Ed. Part 8; Section 4; #5

4

It can be inferred from the passage Martin's

It can be inferred from the passage that Martin’s hypothesis includes which of the following elements? When marine organisms called phytoplankton photosynthesize, they absorb carbon dioxide dissolved in seawater, potentially causing a reduction in the concentration of atmospheric carbon dioxide, a gas that contributes to global warming. However, phytoplankton flourish only in surface waters where iron levels are sufficiently high. Martin therefore hypothesized that adding iron to iron-poor regions of the ocean could help alleviate global warming. While experiments subsequently confirmed that such a procedure increases phytoplankton growth, field tests have shown that such growth does not significantly lower atmospheric carbon dioxide. When phytoplankton utilize carbon dioxide for photosynthesis, the carbon becomes a building block for organic matter, but the carbon leaks back into the atmosphere when predators consume the phytoplankton and respire carbon dioxide. A correct understanding of how phytoplankton photosynthesis utilizes carbon dioxide, A correct prediction about how the addition of iron to iron-poor waters would affect phytoplankton growth, An incorrect prediction about how phytoplankton growth would affect the concentration of atmospheric carbon dioxide

2 Explanations

6

Gravatar Chris Lele, Magoosh Tutor

Oct 10, 2012 • Comment

Saddam Hossain

Why option "A" is correct? Martin only hypothesized that adding iron to iron-poor regions of the ocean could help alleviate global warming. Later experiment find that phytoplankton utilize carbon dioxide for photosynthesis, the carbon becomes a building block for organic matter. So clearly Martin had not given information on how phytoplankton photosynthesis utilizes carbon dioxide, please explain.

Oct 4, 2016 • Reply

Sam Kinsman, Magoosh Tutor

Hi Faud,

Good question - you're right that option A is a bit confusing! Let's take a look at why it is correct.

You're right that Martin hypothesized that adding iron to iron poor regions of the ocean would help reduce global warming. However, he used a correct understanding of how phytoplankton photosynthesis uses carbon dioxide in order to make this hypothesis.

The first sentence in the passage says that when phytoplankton photosynthesize, "they absorb carbon dioxide dissolved in seawater, potentially causing a reduction in the concentration of atmospheric carbon dioxide." In this sentence, the passage says that Martin based his hypothesis on the fact that phytoplankton absorbs carbon dioxide in sea water.

The passage then tells us that atmospheric carbon dioxide contributes to global warming, and that phytoplankton "flourish only in surface waters where iron levels are sufficiently high." We're told that these facts lead Martin to hypothesize "that adding iron to iron-poor regions of the ocean could help alleviate global warming."

The only reason he could conclude that is if he thought that increasing the number of phytoplankton would reduce atmospheric carbon dioxide, right? For that to be true, he must have correctly understood that the phytoplankton would produce a building block for organic matter (or specifically, grow more phytoplankton) when it uses carbon dioxide for photosynthesis.

This is how it can be inferred from the passage that Martin's hypothesis includes a correct understanding of how phytoplankton photosynthesis utilizes carbon dioxide.

Also keep in mind that the experiment did not work because once the phytoplankton has consumed the carbon dioxide, "the carbon leaks back into the atmosphere when predators consume the phytoplankton." So Martin's mistake was not that he misunderstood how phytoplankton photosynthesis utilizes carbon dioxide. Instead, he simply didn't think about what would happen to the phytoplankton after it used the carbon dioxide.

Oct 4, 2016 • Reply

1

Ian K

Misplaced link here.

Dec 7, 2012 • Comment

Lena Brooks, Magoosh Tutor

Hi Ian,

Thanks for letting us know about this error. I just updated the video to the correct explanation! :)

Best,
Lena

Dec 13, 2012 • Reply

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