An analysis of the consequences arising from the non- linearity of the photosynthetic light curves on the values of quantum requirement, as well as on the action spectra and quantum efficiency spectra in dependence of the suspension optical densities is presented. A kinetic model of the oxygen production reaction is elaborated in which in addition to the non-cooperative (Koks)mechanisms a cooperative one is also included. According to this model the oxygen precursors obtained in different oxygen evolving reaction centres could migrate in the surrounding media and recombine. The two...