Question

Number of ATP and NADP required for every CO2 molecule entering the Calvin cycle.

• A. 3 ATP 3 NADP
• B. 2 ATP 2 NADP
• C. 18 ATP 12 NADP
• D. 3 ATP 2 NADP

Hint:

To synthesize 1 molecule of glucose (\(6 \text{ CO}_2\)), the cycle must turn 6 times.
Total requirements = \( 6 \times 3 \text{ ATP} = 18 \text{ ATP} \) and \( 6 \times 2 \text{ NADPH} = 12 \text{ NADPH} \).

Answer 1

The Correct Option is D

Step 1: Work from the whole cycle, not just one CO2.
Making one molecule of glucose (six carbons) through the Calvin cycle uses six turns of the cycle, consuming a total of $18$ ATP and $12$ NADPH.
Step 2: Scale it down to one CO2.
Divide both totals by the six CO2 molecules fixed: $18/6 = 3$ ATP and $12/6 = 2$ NADPH.
Step 3: Sanity check against the phases.
Carboxylation needs no energy, reduction uses 2 ATP and 2 NADPH per CO2, and regeneration adds one more ATP, giving 3 ATP and 2 NADPH overall, which matches.
Final answer: Option 4, 3 ATP and 2 NADPH per CO2 fixed.