For fixing 3 molecules of CO₂ in the Calvin cycle, what is needed?

Explanation

The Calvin cycle, also known as the light-independent reactions of photosynthesis, requires 3 ATP and 2 NADPH molecules for the fixation of each CO₂ molecule. Therefore, for the fixation of 3 CO₂ molecules, the cycle uses a total of 9 ATP and 6 NADPH. Option A is correct, as it matches these requirements. Option B provides the requirements for fixing 6 CO₂ molecules, making it incorrect for this question. Option C suggests an excessive amount of NADPH, and Option D is only adequate for fixing one CO₂ molecule; thus, both are incorrect.