The stage of photosynthesis that does not require light is called the dark or light neutral stage. At this stage CO2 is oxidized to produce sugar, so it is called carbon oxidation reaction or carbon oxidation pathway or carbohydrate making process or carbon oxidation stage. In this process, ATP and NADPH+H+ are called energy compounds for carbon assimilation. Modern scientists have discovered three pathways of carbon assimilation in the photoneutral phase using methods such as radioactive isotopes, autoradiography, paper chromatography etc. Calvin-Basham or C3 cycle, Hatch-Slack or C4 cycle and CAM cycle.