Reading Comprehension

PT122 · S3 · P4 · Q27 Maize

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

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

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

Topic

How maize (corn) and some similar crops became so important and productive due to a unique photosynthesis process.

Framework

Answer / Explain

Main Point

The incredible productivity of maize and some other crops, which has had major impacts on societies, is due to a special adaptation in their photosynthesis process called C-4 photosynthesis, which prevents oxygen from interfering with sugar production. Most Valuable Sentence: The first sentence of paragraph 3: The last paragraph as a whole reveals the explanation for maize's productivity.

P1: The Transformative Impact of Maize

Maize (corn) has radically changed every society that adopted it, dramatically boosting food production and even supporting population growth. The reason for its influence is how productive it is compared to other crops, but the passage sets up a question: why is it so much more productive?

P2: The Biological Challenge of Photosynthesis

This paragraph explains some basics of plant photosynthesis and introduces a problem: in most plants, a key enzyme called rubisco can be interfered with by oxygen, which messes up how efficiently plants make food (sugar) from sunlight and carbon dioxide.

P3: The C-4 Photosynthesis Solution

Certain plants, like maize, have evolved a special way to avoid this problem. In these plants, the process is split up in a way that keeps oxygen away from rubisco. Carbon dioxide gets turned into a special molecule called C-4, which is then used in sugar production. This process—C-4 photosynthesis—explains why crops like maize, sugar cane, and rice can produce so much food.

27.

The passage provides the most support for which one of the following statements?

  1. Correct

    In many plants, rubisco is

    Why this is right

    This doesn't have one great support sentence, but it's sort of a common sense composite of the whole passage. This passage is asking, But why are maize and a few similar crops so much more bountiful than others? And the answer to that question in paragraph 3 is The key to the process is that in these (C4) plants, oxygen and all other atmospheric gases are excluded from the cells containing rubisco. In these C4 plants, rubisco is isolated in airtight tissues, so carbon dioxide has to transform into the nongas C4 molecule in order to go bind with rubisco. In non-C4 plants, carbon dioxide doesn't have to turn into C4 because rubisco isn't isolated in airtight tissues that are impermeable by gases. The last sentence of the 2nd paragraph also reveals evidence that in many plants rubisco is not isolated in some airtight place: Unfortunately, though .... oxygen begins to bind competitively to the enzyme (rubisco), thus interfering with the photosynthetic reaction.

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

    70% picked this

  2. A rubisco molecule contains four

    Unsupported

    This is just a "word salad", where they take a bunch of words from the passage and create an unsupported meaning. The passage mentions "four carbon atoms" when discussing how carbon dioxide turns into a nongas molecule named C-4. That molecule then enters the bundle sheath cells to "mate" with rubisco, but rubisco ain't the thing with 4 carbon atoms.

    2% picked this

  3. Rubisco is needed in photosynthesis

    Contradicted

    This is another Word Salad, where they're just bundling words from the passage together and creating a brand new claim. C-4 plants are the only ones in which carbon dioxide is forced to become a nongas molecule, because in C-4 plants the rubisco is walled off from all gases (trying to prevent oxygen from competitively binding to it). Most plants do photosynthesis without ever converting carbon dioxide into a nongas molecule. So it isn't true to say that anything is needed in photosynthesis to convert CO2 to a nongas molecule, because most photosynthesis doesn't ever involve CO2 becoming a nongas molecule. Even in C-4 plants, where that does occur, rubisco doesn't convert it from gas to nongas. We aren't told what does it, other than "Carbon dioxide, which cannot enter these cells as a gas, first undergoes a series of reactions to form an intermediary, nongas molecule". This is all in preparation for finally entering rubisco's secret chambers. So the CO2 doesn't even "meet" the rubisco until after it's already converted to nongas.

    13% picked this

  4. In maize, rubisco helps protect

    Unsupported: protect against oxygen

    The passage never implies that rubisco helps protect against oxygen buildup. Rubisco is an enzyme that helps with photosynthesis. That's it. In most plants, oxygen buildup in the atmospheric conditions (not necessarily in the leaves) messes with rubisco while it's trying to do its photosynthetic job. We could re-write this answer by saying: In maize, rubisco is protected against the detrimental effects of oxygen.

    11% picked this

  5. Rubisco’s role in the C-4

    Too Strong: optimized

    The passage never talks about when rubisco would be at its best. We could infer that it will do its photosynthetic enzyme job most optimally when oxygen isn't messing with it and competitively binding to it. So in that sense, rubisco will have the worst time when oxygen levels are high relative to carbon dioxide levels. But if we're talking about C-4 plants, then it doesn't matter what the atmospheric oxygen / CO2 balance is. In C-4 plants, the rubisco is sequestered in airtight bundle sheath cells, so it has no interaction with oxygen, regardless of oxygen's levels atmospherically.

    4% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free