What is the name of the second stage of photosynthesis?

The Calvin cycle is commonly identified as the second stage of photosynthesis. It follows the light-dependent reactions and uses the ATP and NADPH made during those reactions to incorporate carbon dioxide into organic molecules.

The cycle takes place in the stroma, the fluid-filled region surrounding the thylakoid membranes inside a chloroplast. It begins when carbon dioxide is attached to the five-carbon molecule RuBP. The unstable intermediate quickly splits into two three-carbon molecules, which are then processed using energy and reducing power from ATP and NADPH.

The Calvin cycle does not require darkness; “light-independent reactions” is a better description than “dark reactions.” The cycle can operate in daylight when its required chemical inputs are available. It eventually produces triose phosphate, a three-carbon sugar that can be used to form glucose and other carbohydrates, while most of the intermediate molecules regenerate RuBP so the cycle can continue.

The name honors Melvin Calvin, James Bassham, and Andrew Benson, whose research in the 1940s helped map the pathway. Electron transport belongs to the first stage, while the Krebs cycle is part of cellular respiration.