Question

In $C_3$ cycle for the fixation of every $CO_2$ molecule, the reduction and regeneration steps require:

• A. $3\, ATP$ and $2\, NADPH_2$
• B. $2 \,ATP$ and $2\, NADPH_2$
• C. $2\, ATP$ and $3\, NADPH_2$
• D. $3\, ATP$ and $3 \,NADPH_2$
• E. $3\, ATP$ and $1\, NADPH_2$

Answer 1

Answer: (A)

The Calvin cycle or $C_{3}$ cycle proceeds in three stages (1) carboxylation, during which $CO_{2}$ combines with ribulose $-1$, $5$-bisphosphate; $(2) $ reduction, during which carbohydrate is formed at the expense of the photochemically made ATP (two molecules) and NADPH (two molecules) and (3) regeneration during which the $CO_{2}$ acceptor ribulose-1, 5-bisphosphate is formed again so that the cycle continues. The regeneration step requires one ATP for phosphorylation to form RuBP