Carbon dioxide from the atmosphere diffuses into the leaf through stomata and reaches stroma of chloroplast. In stroma, carbon dioxide combines with ribulose biphosphate (RuBP) in the presence of an enzyme called Rubisco, producing two molecules of glycerate 3 phosphate (GP). Glycerate 3 phosphate is reduced to triose phosphate by using both reduced NADP and energy from ATP. Triose phosphate then can be converted into organic substances that plants require, such as starch, cellulose, lipids and RuBP.