Reading ComprehensionDifficulty: Hard

PT122 S3 P4 Q24 Explanation

Maize

A free, expert breakdown of this official LSAT Reading Comprehension question.

TopicsLocal PurposeScience

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Passage

Every culture that has adopted the cultivation of maize—also known as corn—has been radically changed by it. This crop reshaped the cultures of the Native Americans who first cultivated it, leading to such developments as the adoption of agrarian and in some cases urban lifestyles, and much of the explosion of European much more bountiful than others? Modern biochemistry has revealed the physical mechanism underlying maize’s impressive productivity.

To obtain the hydrogen they use in the production of carbohydrates through photosynthesis, all plants split water into its constituent elements, hydrogen and oxygen. They use the resultant hydrogen to form one of the molecules they need for energy, but the oxygen is released into the atmosphere. During photosynthesis, carbon dioxide that atmospheric conditions, oxygen begins to bind competitively to the enzyme, thus interfering with the photosynthetic reaction.

Some plants, however, have evolved a photosynthetic mechanism that prevents oxygen from impairing photosynthesis. These plants separate the places where they split water atoms into hydrogen and oxygen from the places where they build sugars from carbon dioxide. Water molecules are split, as in all plants, in specialized chlorophyll-containing structures in the Such C-4 plants as sugar cane, rice, and maize are among the world’s most productive crops.

What this question is testing

Local Purpose

Your task

Identify why the author included the referenced detail at that point in the passage — its function, not its content.

Common trap

Answers that merely repeat or summarize the topic of the detail instead of describing the role it plays.

Winning move

Ask what job the detail does for the paragraph, then for the passage's broader point.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
24.

The author’s reference to “all other atmospheric gases” in the third paragraph plays which one of the following

Answer choices

  1. Unsupported Causal Relationship14% picked this

    It indicates why certain atmospheric conditions can cause excess oxygen to build up and thus hinder photosynthesis in non-C-4 plants as

    The fact that "All atmospheric gases are locked out of the cells with rubisco" explains why excess oxygen can build up in the atmosphere and hinder non-C-4 plants? The role of this paragraph is to talk about C-4 plants. It didn't seem like this phrase we're being asked about was a callback to the 2nd paragraph or a causal explanation for what's discussed at the end of the 2nd paragraph. It's not like we can say, "Because oxygen is kept out of the bundle sheath cells that C-4 plants have, oxygen builds up in the atmosphere and messes up non-C-4 plants."

  2. Unsupported: other gas interferes22% picked this

    It supports the claim advanced earlier in the paragraph that oxygen is not the only atmospheric gas whose presence in the

    There is never any mention that any other kind of atmospheric gas can interfere with photosynthesis, so we can't say the role of this phrase was to support such a claim.

  3. Unsupported: uses other gases4% picked this

    It supports the conclusion that non-C-4 photosynthesis makes use of several atmospheric gases that C-4

    There is never any mention that any other kind of atmospheric gases besides oxygen and carbon dioxide are used in non-C-4 photosynthesis, so we can't say the role of this phrase was to support such a claim. Also, since this part of the passage is about C-4 photosynthesis, it should sound like a red flag to say that it's here to support a conclusion about non-C-4 photosynthesis.

  4. Correct55% picked this

    It explains why carbon dioxide molecules undergo the transformations described later in the paragraph before participating in

    Why this is right

    The fact that "no atmospheric gases can enter the cells where the rubisco is" explains why carbon dioxide molecules undergo a series of reactions to form an intermediary, nongas molecule named C-4? Yeah, I guess it does! It does say, 'Carbon dioxide, which cannot enter these cells as a gas (because oxygen and all other atmospheric gases are excluded from the cells containing rubisco), first undergoes a series of reactions to form a nongas molecule". This seems like a very hard answer to predict, but it does make logical sense to relate the phrase in question to the nongas C-4 molecule.

    Skill tested: Local Purpose · how this choice captures the passage's function is the move to repeat next time.

  5. Unsupported: constant oxygen5% picked this

    It advances a broader claim that oxygen levels remain constant in C-4 plants in spite of

    There is never any mention of this extreme claim that oxygen levels remain constant in C-4 plants. We're only being told that oxygen is kept out of the bundle sheath cells. In those cells, sure the level of oxygen remains at a constant level of zero. But in the rest of the plant, the levels of oxygen may vary.

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