AIIMS 2019 Botany C₄ Cycle Assertion Reason Question
Assertion: In C4 cycle, first stable product has 4 carbon compound
Reason: In C4 plants, C3 cycle is absent
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Correct Answer
Detailed Explanation
In the C₄ cycle, oxaloacetic acid (a 4-carbon compound) is indeed the first stable product formed when CO₂ is fixed, but the mention of a "C₃ cycle" is misleading. The C₃ cycle refers to the Calvin cycle, which is distinct from the C₄ cycle and primarily involves 3-carbon compounds like 3-phosphoglycerate (3-PGA). Therefore, while the C₄ cycle operates alongside the Calvin cycle in certain plants, the statement's phrasing does not accurately represent their relationship, making option C the most appropriate choice. Options A and B are incorrect as they imply a direct connection between the C₄ and C₃ cycles that is not clearly articulated in the question.
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