It is divided into NADH (reduced coenzyme I) and NADPH (reduced coenzyme II).
It is used for respiration (the second stage of anaerobic respiration or the third stage of aerobic respiration) and photosynthesis (the third stage of reducing C3) respectively to generate NAD+ (oxidized coenzyme I) and NADP+ (oxidized coenzyme II). These two oxidized coenzymes return to the original place where reduced hydrogen is produced and continue to combine with hydrogen, and then participate in the reaction according to this cycle.