Chlorophyll the last step, the conversion of protochlorophyllide to chlorophyll, is light-dependent and such plants are pale (etiolated) if grown in darkness. Non-vascular plants and green algae have an additional light-independent enzyme and grow green even in darkness. Chlorophyll itself is bound to proteins and can transfer the absorbed energy in the required direction. Protochlorophyllide occurs mostly in the free form and, under light conditions, acts as a photosensitizer, forming highly toxic free radicals. Hence, plants need an efficient mechanism of regulating the amount of chlorophyll precursor. In angiosperms, this is done at the step of aminolevulinic acid (ALA), one of
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