Photosynthesis consists of two processes : light energy conversion to biochemical energy by a photochemical reaction, and CO2 reduction to organic compounds such as sugar phosphates, through the use of this biochemical energy by Calvin-cycle enzymes. Under certain conditions, however, instead of reducing CO2, a few groups of microalgae and Cyanobacteria consume biochemical energy to produce molecular hydrogen. Hydrogenase enzyme is capable of hydrogen production.