Question

The Calvin cycle proceeds in three stages.
(1) Reduction, during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH.
(2) Regeneration, during which the carbon dioxide acceptor ribulose-1,5-biphosphate is formed.
(3) Carboxylation, during which carbon dioxide combines with ribulose-1, 5-biphosphate.
Identify the correct sequence from the following.

• A. 3, 1, 2
• B. 3, 2, 1
• C. 1, 2, 3
• D. 2, 1, 3
• E. None of the above

Answer 1

The correct option is A 3, 1, 2

Calvin cycle begins with fixation of $C{O}_2$ into 3 C sugar by the process of carboxylation. RUBISCO, present in the chloroplast stroma catalyzes carboxylation of ribulose-1, 5-biphosphate (RuBP) followed by immediate splitting of unstable product into 3-phosphoglyceric acid. Carboxylation is followed by a series of reduction reactions wherein 3 C compound 3-phosphoglyceric acid is reduced into 3 C compounds glyceraldehydes 3-phosphate (G3P); the reduction reactions are energized by ATP and NADPH serve as an electron donor. Three turns of Calvin cycle obtains 6 molecules of G3P, out of which one is used for glucose formation and rest are used in regeneration phase. The last phase of Calvin cycle, the regeneration phase ensures the continuous supply of RuBP for carboxylation and regenerates it using G3P. Thus, the correct answer is option A.