outline the three main stages of the Calvin cycle: • rubisco catalyses the fixation of carbon dioxide by combination with a molecule of ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of glycerate 3-phosphate (GP), a 3C compound • GP is reduced to triose phosphate (TP) in reactions involving reduced NADP and ATP • RuBP is regenerated from TP in reactions that use ATP