Calvin cycle | Dark reaction | C3 Cycle | Photosynthesis | Home Revise

The dark reaction, or Calvin cycle, is the biosynthetic phase of photosynthesis, occurring in the chloroplast stroma. It's also called the light-independent reaction, where carbon dioxide fixation leads to carbohydrate synthesis (glucose). Discovered by Melvin Calvin and Andy Benson, it's also known as the Calvin-Benson cycle.

Carbon dioxide enters the cycle and is accepted by ribulose bisphosphate (RuBP). The enzyme RuBisCO (ribulose bisphosphate carboxylase) catalyzes this fixation. ATP and NADPH, produced during the light reaction, provide the energy and hydrogen needed to fix carbon dioxide and produce glucose.

The overall chemical reaction is: 6 RuBP + 6 CO2 + 18 ATP + 12 NADPH + 12 H+ ions → 6 RuBP + C6H12O6 + 18 Pi + 18 ADP + 12 NADP + 6 H2O. RuBP is regenerated, allowing the cycle to continue. The dark reaction occurs almost simultaneously with the light reaction, with a tiny gap of less than one thousandth of a second.