Q.For every CO2 molecule entering the C3 cycle, the number of ATP & NADPH required
a. 2ATP + 2NADPH
b. 2ATP + 3NADPH
c. 3ATP + 2NADPH
d. 3ATP + 3NADPH

The Calvin cycle (also called the C3 cycle, the dark reaction, or the Photosynthetic Carbon Reduction cycle) is the pathway that uses the ATP and NADPH+H+ generated by the light reaction to fix and reduce CO2 into carbohydrate, running in the chloroplast stroma and named for M. Calvin and A. Benson, who worked it out in 1957. Its CO2 acceptor is the 5-carbon compound ribulose 1,5-bisphosphate (RuBP), and the enzyme RuBisCO fixes CO2 onto it; because the first stable product is the 3-carbon compound phosphoglyceric acid (PGA), the cycle is called C3. The cycle has three phases. Carboxylation: RuBisCO combines RuBP (5C) with CO2 to form an unstable 6-carbon intermediate that splits into two molecules of PGA (3C). Reduction (glycolytic reversal): each PGA is phosphorylated by ATP into 1,3-bisphosphoglycerate, then reduced by NADPH+H+ into glyceraldehyde-3-phosphate (G3P), which isomerises to DHAP. Regeneration: most of the G3P/DHAP pool cycles back, through 4-, 5-, 6- and 7-carbon sugar-phosphate intermediates, to ribulose-5-phosphate, which is phosphorylated by ATP back into RuBP, closing the cycle; only a small net fraction of G3P is exported to build hexose sugar and starch. For every CO2 molecule fixed, the cycle consumes 3 ATP and 2 NADPH+H+ (2 ATP f …