lightindependent

Lightindependent refers to the portion of photosynthesis that does not require light directly. In plants, algae, and many bacteria, these reactions occur in the stroma of chloroplasts and are collectively known as the Calvin cycle, or the reductive pentose phosphate cycle.

During the cycle, carbon dioxide is fixed by the enzyme RuBisCO, combining CO2 with ribulose-1,5-bisphosphate to form 3-phosphoglycerate. Through a series of reductions and phosphorylations powered by ATP and NADPH supplied by the light-dependent reactions, 3-PGA is converted into glyceraldehyde-3-phosphate. Most of the G3P is used to regenerate RuBP, enabling continued carbon fixation; a portion exits the cycle and is ultimately used to synthesize glucose and other carbohydrates.

Although called light-independent, the cycle relies on ATP and NADPH produced by light reactions and thus cannot proceed without at least some photosynthetic activity. It is sometimes referred to as the dark reactions, a historical term that can be misleading because the reactions occur in light when energy carriers are available.

Organisms that perform these reactions include plants, algae, and cyanobacteria, and the Calvin cycle is a central pathway for carbon assimilation and biomass production. The efficiency of the cycle can be influenced by CO2 concentration, temperature, and the availability of ATP and NADPH.