Robert Hill thought that a complex of reactions consisting of an intermediate to cytochrome b (now a plastoquinone), another is from cytochrome f to a step in the carbohydrate - generating mechanisms. These are linked by plastoquinone, which does require energy to reduce cytochrome f for it is a sufficient reductant. Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. The Hill reaction is as follows:
what is the source of oxygen inside the plant during photosynthesis
chloroplasts