In an attempt to produce a coffee plant that would yield beans containing no caffeine, the synthesis of a substance...

GMAT Critical Reasoning : (CR) Questions

Source: Official Guide

Critical Reasoning

Paradox

HARD

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Notes

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In an attempt to produce a coffee plant that would yield beans containing no caffeine, the synthesis of a substance known to be integral to the initial stages of caffeine production was blocked either in the beans, in the leaves, or both. For those plants in which synthesis of the substance was blocked only in the leaves, the resulting beans contained no caffeine.

Any of the following, if true, would provide the basis for an explanation of the observed results EXCEPT:

In coffee plants, the substance is synthesized only in the leaves and then moves to the beans, where the initial stages of caffeine production take place.

In coffee plants, the last stage of caffeine production takes place in the beans using a compound that is produced only in the leaves by the substance.

In coffee plants, the initial stages of caffeine production take place only in the beans, but later stages depend on another substance that is synthesized only in the leaves and does not depend on the blocked substance.

In coffee plants, caffeine production takes place only in the leaves, but the caffeine then moves to the beans.

Caffeine was produced in the beans of the modified coffee plants, but all of it moved to the leaves, which normally produce their own caffeine.

Solution

Passage Analysis:

Text from Passage	Analysis
In an attempt to produce a coffee plant that would yield beans containing no caffeine, the synthesis of a substance known to be integral to the initial stages of caffeine production was blocked either in the beans, in the leaves, or both.	What it says: Scientists tried to make caffeine-free coffee by blocking a key substance needed for caffeine production in different parts of the plant What it does: Sets up the experimental approach and context for what we're about to learn What it is: Study background/experimental design Visualization: Coffee plants with blocked substance → Beans (blocked), Leaves (blocked), or Both (blocked) → Goal: Zero caffeine beans
For those plants in which synthesis of the substance was blocked only in the leaves, the resulting beans contained no caffeine.	What it says: When they blocked the substance only in leaves (not beans), the beans still ended up with no caffeine What it does: Presents the surprising experimental result that connects to the setup - blocking in leaves affected beans What it is: Study finding/experimental result Visualization: Leaves (substance blocked) → Beans (unexpectedly caffeine-free) vs Expected: Leaves (substance blocked) → Beans (should still have caffeine)

Argument Flow:

The passage presents an experimental setup followed by a specific, somewhat surprising result. It establishes the goal (caffeine-free beans), describes the method (blocking substance in different plant parts), and then reveals an unexpected finding (blocking in leaves alone still eliminated caffeine from beans).

Main Conclusion:

This passage doesn't contain a conclusion - it's presenting experimental data that needs explanation. The surprising result is that blocking caffeine-production substance only in leaves somehow prevented caffeine formation in the beans.

Logical Structure:

This is a data presentation rather than an argument structure. We have experimental design (blocking substance in different locations) leading to an unexpected result (leaf-blocking affects bean caffeine content). The logical puzzle is explaining how leaf-blocking impacts bean chemistry.

Prethinking:

Question type:

Paradox - EXCEPT: We need to find four options that WOULD explain the surprising result (blocking substance only in leaves led to caffeine-free beans), and one option that would NOT explain this result.

Precision of Claims

The key claim is very specific: blocking the substance ONLY in leaves (not in beans) resulted in beans with NO caffeine. This is surprising because we'd expect that if the beans themselves can still produce the substance, they should still make caffeine.

Strategy

Since this is an EXCEPT question for a paradox, we skip the normal prethinking process. Instead, we recognize that four answer choices will provide reasonable explanations for why blocking the substance only in leaves prevented caffeine production in beans, while one choice will either be irrelevant or fail to explain this connection between leaves and beans.

Answer Choices Explained

In coffee plants, the substance is synthesized only in the leaves and then moves to the beans, where the initial stages of caffeine production take place.

This explains the result perfectly. If the substance is only made in leaves and then travels to beans where caffeine production happens, then blocking the substance in leaves would cut off the supply to beans, preventing caffeine production. This directly explains why leaf-blocking affects bean caffeine content.

In coffee plants, the last stage of caffeine production takes place in the beans using a compound that is produced only in the leaves by the substance.

This also provides a solid explanation. If caffeine's final stage requires a compound that leaves produce using the blocked substance, then blocking that substance in leaves would prevent the final compound from being made, stopping caffeine production in beans. The connection between leaves and beans is clear.

This choice fails to explain our surprising result. It says initial caffeine stages happen only in beans, and later stages need another leaf substance that doesn't depend on the blocked substance. If this were true, blocking our specific substance in leaves shouldn't affect caffeine production at all - the beans could still do initial stages, and the later stages would use an unaffected leaf substance. This doesn't explain why we got caffeine-free beans.

In coffee plants, caffeine production takes place only in the leaves, but the caffeine then moves to the beans.

This explains the result well. If all caffeine production happens in leaves and then caffeine moves to beans, blocking the key substance in leaves would prevent any caffeine from being made in the first place. No caffeine production means no caffeine to move to beans, explaining the caffeine-free result.

Caffeine was produced in the beans of the modified coffee plants, but all of it moved to the leaves, which normally produce their own caffeine.

This provides an explanation, though somewhat convoluted. It suggests caffeine was actually made in beans but then moved to leaves. While this scenario seems unusual, it would technically explain why beans ended up caffeine-free - the caffeine left the beans and went to the leaves.

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