Question

For fixing one molecule of $C{O}_2$ in Calvin cycle, .......... are required.

• A. 3 ATP + 1 NADPH${}_2$
• B. 3 ATP + 2 NADPH${}_2$
• C. 2 ATP + 3 NADPH${}_2$
• D. 3 ATP + 3 NADPH${}_2$

Answer 1

The correct option is B 3 ATP + 2 NADPH${}_2$

CO$_2$ fixation in dark reaction was thoroughly worked out by M. Calvin. Therefore, the complete pathway is called Calvin cycle. And the first stable compound is a three carbon compound, (3- phosphoglyceric acid) , the cycle is called $C_3$ cycle.

It consists of three major steps:

1. Carboxylation: Zero ATP and zero NADPH.

2. Reversal of glycolysis: Two ATP and two NADPH.

3. Regeneration of RuBP: One ATP and zero NADPH.

Hence for every CO$_2$ molecule entering the calvin cycle, 3 molecules of ATP and 2 of NADPH are required.

So, the correct answer is '3ATP + 2 NADPH${}_2$'.