Calvin cycle or dark reaction is a synthetic process in which carbon dioxide is reduced to carbohydrates. It takes place in the stroma of chloroplasts. The entire process runs in a cycle. It utilizes ATP and NADPH2. This reaction is independent of light.
The Calvin cycle begins when a molecule of carbon dioxide bonds with the five-carbon sugar ribulose diphosphate. A series of reactions ensue (which involve the NADPH molecule from noncyclic electron flow and convert it back to an NADP+ molecule), producing another molecule of ribulose diphosphate and a molecule of glyceraldehyde phosphate