Question: 108. How many molecules of ATP and NADPH are required for every molecule of \mathrm{CO}_{2} fixed in the Calvin cycle?
(1) 2 molecules of ATP and 3 molecules of NADPH.
(2) 2 molecules of ATP and 2 molecules of NADPH.
(3) 3 molecules of ATP and 3 molecules of NADPH.
(4) 3 molecules of ATP and 2 molecules of NADPH.
Answer: Option (4)
Explanation:
The Calvin cycle fixes carbon dioxide into carbohydrates using energy and
reducing power obtained from the light reactions.
For fixation of 6 molecules of \mathrm{CO}_{2},
the Calvin cycle requires 18 molecules of ATP and 12 molecules of NADPH.
Therefore, for fixation of 1 molecule of \mathrm{CO}_{2},
the requirement is \frac{18}{6}=3 molecules of ATP and \frac{12}{6}=2 molecules of NADPH.
Hence, for every molecule of \mathrm{CO}_{2} fixed, 3 molecules of ATP and 2 molecules of NADPH are required.