This part of photosynthesis takes part in the stroma located in the chloroplast. The Calvin cycle involves the reduction of carbon dioxide and requires hydrogen from NADPH and ATP to produce energy. In the first part of the Calvin cycle a 5 carbon compound called ribulose bisphosphate will combine with a 6 carbon compound, the compound however is unstable and will split into 2 molecules of a 3 carbon compound, this is called glycerate 3 phosphate. This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase. glycerate (http://faculty.southwest.tn.edu,