Photosynthetic carbon cycle The basic mode of carbon assimilation (conversion of carbon dioxide into sugar or its phosphate ester) in photosynthesis. Also known as calvin cycle, pentose phosphate reduction cycle and pentose phosphate reduction pathway. It is ubiquitous in green plants, cyanobacteria and various photosynthetic bacteria. CO2 fixed by other carbon assimilation pathways such as C4 pathway and CAM pathway (such as acid metabolism of Sedum) can only be reduced to sugar through photosynthetic carbon cycle. Therefore, it is the only way for the formation of most organic matter on earth.