(introduction...)

Microalgae are primitive microscopic plants living in aqueous environments. Cyanobacteria, formerly known as blue-green algae, are now recognized as bacteria since the anatomical characteristics of their cells are prokaryotic (bacterial type). Miroalgae and Cyanobacteria along with higher plants, are capable of oxygenic photosynthesis according to the following reaction:

CO₂ + H₂O ® 6 [CH₂O] + O₂.
organic compounds

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 (Fig. 5-2; 5-3). Hydrogenase and nitrogenase enzymes are both capable of hydrogen production.