Unsolved problems in the study of primary reactions in photosynthesis

An analysis is made of some problems involving electron transport to the oxidized photoactive pigments in photosynthesis. Electron donors for chlorophyll $a^+$ may be $H_2O$ or $X(HCO_3^-)$. On the basis of published experimental data, it is concluded that the primary electron donor is most likely the compound $X(HCO_3^-)$.