Chlorophyll a chemical energy but is not the only pigment that can be used for photosynthesis. All oxygenic photosynthetic organisms use chlorophyll "a", but differ in accessory pigments like chlorophylls "b". Chlorophyll "z" can also be found in very small quantities in the green sulfur bacteria, an anaerobic photoautotroph. These organisms use bacteriochlorophyll and some chlorophyll "a" but do not produce oxygen. Anoxygenic photosynthesis is the term applied to this process, unlike oxygenic photosynthesis where oxygen is produced during the light reactions of photosynthesis. The molecular structure of chlorophyll "a" consists of a chlorin ring, whose four nitrogen atoms surround a central
Photosynthesis Cycle. Nobel Prize-winning scientist Rudolph A. Marcus was able to discover the function and significance of the electron transport chain. Otto Heinrich Warburg and Dean Burk discovered the I-quantum photosynthesis reaction that splits the CO, activated by the respiration. In 1950, first experimental evidence for the existence of photophosphorylation "in vivo" was presented by Otto Kandler using intact "Chlorella" cells and interpreting his findings as light-dependent ATP formation. In 1954, Daniel I. Arnon et al. discovered photophosphorylation "in vitro" in isolated chloroplasts with the help of P. Louis N.M. Duysens and Jan Amesz discovered that chlorophyll a will absorb one