AIIMS 2019 Botany C₃ and C₄ Cycles Assertion Reason Question
Assertion: In C₃ cycle, the first stable compound is 3C compound Reason: In C₄ plants Calvin 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 C₃ cycle, the first stable compound formed is 3-phosphoglycerate (3-PGA), which is indeed a 3-carbon (3C) compound, making the assertion true. However, the reason is false because C₄ plants do utilize the Calvin cycle, albeit with an initial fixation of CO₂ into a 4-carbon compound (oxaloacetate) before entering the Calvin cycle. Therefore, while the assertion is true, the reason does not correctly explain it, validating option C. Options A and B are incorrect because they either misattribute the relationship between the assertion and reason or incorrectly state the truth of the reason. Option D is incorrect as the assertion is true.
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