Every Culture that has Adopted the Cultivation of Maize

Reading Passage Question

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 populations after the fifteenth century was driven by the introduction of maize together with another crop from the Americas, potatoes. The primary reason for this plant’s profound influence is its sheer productivity. With maize, ancient agriculturalists could produce far more food per acre than with any other crop, and early Central Americans recognized and valued this characteristic of the plant. But why are maize and a few similar crops so 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 the plant takes in from the atmosphere is used to build sugars within the plant. An enzyme, rubisco, assists in the sugar forming chemical reaction. Because of its importance in photosynthesis, rubisco is arguably the most significant enzyme in the world. Unfortunately, though, when the concentration of oxygen relative to carbon dioxide in a leaf rises to a certain level, as can happen in the presence of many common 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 specialised chlorophyll-containing structures in the green leaf cells, but the rubisco is sequestered within airtight tissues in the centre of the leaf. The key to the process is that in these plants, oxygen and all other atmospheric gases are excluded from the cells containing rubisco. These cells, called the bundle sheath cells, surround the vascular structures of the leaf—structures that function analogously to human blood vessels. Carbon dioxide, which cannot enter these cells as a gas, first undergoes a series of reactions to form an intermediary, non gas molecule named C-4 for the four carbon atoms it contains. This molecule enters the bundle sheath cells and there undergoes reactions that release the carbon dioxide that will fuel the production of carbohydrates (e.g., sugars).Taking its name from the intermediary molecule, the entire process is called C-4 photosynthesis. Such C-4 plants as sugar cane, rice, and maize are among the world’s most productive crops.

‘Every culture that has adopted the cultivation of maize’ is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 7 comprehension questions.

The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. Which one of the following most accurately states the main point of the passage?

(A) The greater productivity of maize, as compared with many other crops, is due to its C-4 photosynthetic process, in which the reactions that build sugars are protected from the effects of excess oxygen.
(B) Because of their ability to produce greater quantities and higher qualities of nutrients, those plants, including maize, that use a C-4 photosynthetic process have helped to shape the development of many human cultures.
(C) C-4 photosynthesis, which occurs in maize, involves a complex sequence of chemical reactions that makes more efficient use of available atmospheric hydrogen than do photosynthetic reactions in non-C-4 plants.
(D) The presence of the enzyme rubisco is a key factor in the ability of C-4 plants, including maize, to circumvent the negative effects of gases such as oxygen on the production of sugars in photosynthesis.
(E) Some of the world’s most productive crop plants, including maize, have evolved complex, effective mechanisms to prevent atmospheric gases that could bind competitively to rubisco from entering the plants’ leaves.

2. Which one of the following most accurately states the main point of the passage?

(A) The greater productivity of maize, as compared with many other crops, is due to its C-4 photosynthetic process, in which the reactions that build sugars are protected from the effects of excess oxygen.
(B) Because of their ability to produce greater quantities and higher qualities of nutrients, those plants, including maize, that use a C-4 photosynthetic process have helped to shape the development of many human cultures.
(C) C-4 photosynthesis, which occurs in maize, involves a complex sequence of chemical reactions that makes more efficient use of available atmospheric hydrogen than do photosynthetic reactions in non-C-4 plants.
(D) The presence of the enzyme rubisco is a key factor in the ability of C-4 plants, including maize, to circumvent the negative effects of gases such as oxygen on the production of sugars in photosynthesis.
(E) Some of the world’s most productive crop plants, including maize, have evolved complex, effective mechanisms to prevent atmospheric gases that could bind competitively to rubisco from entering the plants’ leaves.

3. Assuming that all other relevant factors remained the same, which one of the following, if it developed in a species of plant that does not have C-4 photosynthesis, would most likely give that species an advantage similar to that which the author attributes to C-4plants?

(A) Water is split into its constituent elements in specialised chlorophyll-containing structures in the bundle sheath cells.
(B) An enzyme with which oxygen cannot bind performs the role of rubisco.
(C) The vascular structures of the leaf become impermeable to both carbon dioxide gas and oxygen gas.
(D) The specialised chlorophyll-containing structures in which water is split surround the vascular structures of the leaf.
(E) An enzyme that does not readily react with carbon dioxide performs the role of rubisco in the green leaf cells.

4. The author’s reference to “all other atmospheric gases” (Highlighted) plays which one of the following roles in the passage?

(A) It indicates why certain atmospheric conditions can cause excess oxygen to build up and thus hinder photosynthesis in non-C-4 plants as described in the previous paragraph.
(B) It supports the claim advanced earlier in the paragraph that oxygen is not the only atmospheric gas whose presence in the leaf can interfere with photosynthesis.
(C) It supports the conclusion that non-C-4 photosynthesis makes use of several atmospheric gases that C-4 photosynthesis does not use.
(D) It explains why carbon dioxide molecules undergo the transformations described later in the paragraph before participating in photosynthesis in C-4 plants.
(E) It advances a broader claim that oxygen levels remain constant in C-4 plants in spite of changes in atmospheric conditions.

5. The author’s reference to “all other atmospheric gases” (Highlighted) plays which one of the following roles in the passage?

(A) It indicates why certain atmospheric conditions can cause excess oxygen to build up and thus hinder photosynthesis in non-C-4 plants as described in the previous paragraph.
(B) It supports the claim advanced earlier in the paragraph that oxygen is not the only atmospheric gas whose presence in the leaf can interfere with photosynthesis.
(C) It supports the conclusion that non-C-4 photosynthesis makes use of several atmospheric gases that C-4 photosynthesis does not use.
(D) It explains why carbon dioxide molecules undergo the transformations described later in the paragraph before participating in photosynthesis in C-4 plants.
(E) It advances a broader claim that oxygen levels remain constant in C-4 plants in spite of changes in atmospheric conditions.

6. The author of the passage would be most likely to agree with which one of the following statements?

(A) Maize’s impressive productivity cannot be understood without an understanding of its cultural influences.
(B) Maize is an example of a plant in which oxygen is not released as a by-product of photosynthesis.
(C) Maize’s high yields are due not only to its use of C-4 but also to its ability to produce large quantities of rubisco.
(D) Until maize was introduced to Europeans by Native Americans, European populations lacked the agricultural techniques required for the cultivation of C-4 plants.
(E) Maize’s C-4 photosynthesis is an example of an effective evolutionary adaptation that has come to benefit humans

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

(A) In many plants, rubisco is not isolated in airtight tissues in the centre of the leaf.
(B) A rubisco molecule contains four carbon atoms.
(C) Rubisco is needed in photosynthesis to convert carbon dioxide to a nongar molecule.
(D) In maize, rubisco helps protect against the detrimental effects of oxygen buildup in the leaves.
(E) Rubisco’s role in the C-4 process is optimised when oxygen levels are high relative to carbon dioxide levels.

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