The Calvin cycle is a metabolic pathway that is found in the stroma of the chloroplast. Carbon enters the pathway in the form of CO2 and exits in the form of sugar.
The Calvin cycle spends ATP as an energy source and consumes NADPH2 as a reducing power for adding high-energy electrons to make sugar. There are three phases in the Calvin cycle. Phase one is carbon fixation. In phase one, CO2 is incorporated into ribulose bisphosphate (RuBP), which is a five carbon sugar. Phase two is the reduction phase, in which ATP and NADPH2 from the light reactions are used to convert three-phosphoglycerate to three-phosphate. Also, the three-carbon carbohydrate precursor is converted to glucose and other sugars. Phase three is regeneration, in which more ATP is used to convert some of the pool of glyceraldehyde three-phosphate back to ribulose bisphosphate and the acceptor for CO2.