PT122.S3.P4.Q27 > Analytics

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Every culture that has adopted the cultivation of maize—also known as corn—has been radically changed by it. ███

intro topic · Influence of maize

explain significance · of maize

Contributed to development of agrarian and urban societies, and European population growth

hypothesis · Maize's influence is due to its productivity

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phenomenon · Productivity of maize

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Intro to hypothesis · Biochemistry provides the answer

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Context · Explanation of photosynthesis

Water splits into hydrogen and oxygen, hydrogen produces energy. Meanwhile, carbon dioxide builds sugars with help from enzyme (rubisco).

Problem · Too much oxygen interferes with photosynthesis

Enzyme supposed to work with carbon dioxide, but oxygen binds to enzyme instead, meaning less enzyme available to work with carbon dioxide

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Solution (hypothesis) · Different method of photosynthesis

Enzyme (rubisco) is kept separate from atmospheric gases (e.g., oxygen and carbon dioxide)

Complication with hypothesis · Carbon dioxide cannot reach enzyme as gas

Solution: Carbon dioxide becomes nongas molecule (C-4) in order to reach enzyme and drive photosynthesis

Strengthen hypothesis · Other highly productive crops use this method of photosynthesis

Passage Style

Phenomenon-hypothesis (RC)

Single position

27.

The passage provides the most ███████ ███ █████ ███ ██ ███ █████████ ███████████

In many plants, ███████ ██ ███ ████████ ██ ████████ ███████ ██ ███ ██████ ██ ███ █████

Strongly supported. The unusual productivity of C-4 plants, as compared to many other plants, is the result of rubisco's isolation in airtight tissues in the center of the leaf. This prevents oxygen gas from interfering with with rubisco, while in other, less-productive, non-C-4 plants, we know that oxygen does interfere with rubisco. We can infer that non-C-4 plants therefore don’t isolate rubisco from oxygen the way C-4 plants do.

64%

A rubisco molecule ████████ ████ ██████ ██████

Misdirection. C-4 molecules contain four carbon atoms. The author doesn’t discuss rubisco’s chemical composition.

Rubisco is needed ██ ██████████████ ██ ███████ ██████ ███████ ██ █ ██████ █████████

Unsupported. Rubisco’s role is to assist carbon dioxide in building sugars (which are presumably nongas molecules), but we don’t know whether rubisco directly converts carbon dioxide into anything. Also, while rubisco is important and helpful to this process, we don’t know if it’s strictly necessary. (C) is also pulling a misdirection: in C-4 plants, carbon dioxide must first be converted to a nongas molecule before it can react with rubisco. (We’re never told what coverts carbon dioxide into that nongas molecule.)

15%

In maize, rubisco █████ ███████ ███████ ███ ███████████ ███████ ██ ██████ ███████ ██ ███ ███████

Misdirection. Rubisco is the target of oxygen buildup, in maize or any other plant. Oxygen binds to rubisco, which has the detrimental effect of preventing rubisco from properly carrying out its role in photosynthesis. In maize, through, bundle sheath cells are there to help protect rubisco from the detrimental effects of oxygen buildup.

14%

Rubisco's role in ███ ███ ███████ ██ █████████ ████ ██████ ██████ ███ ████ ████████ ██ ██████ ███████ ███████

Unsupported. The author does touch on the effects of increased oxygen levels in P2, but she says that increased oxygen has a negative effect on rubisco—and she’s talking about non-C-4 plants. In the C-4 process, meanwhile, oxygen is kept away from rubisco altogether. There’s no indication that the C-4 process improves when the ratio of oxygen to carbon dioxide is high. If anything, we should expect that things improve when there’s a low ratio of oxygen to carbon dioxide, because that means there’s relatively more carbon dioxide to fuel the photosynthesis reactions that rubisco helps with.

PrepTest 122 - Section 3 - Passage 4 - Question 27

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