Origin of oxygen as a byproduct of noncyclic photophosphorylation?
Plant, green algae and some bacterial photosynthesis depend on
noncyclic electron flow, which means that electrons lost by the
photosystems are not recycled back to the photosystems but instead
passed on to NADPH. To replenish electrons lost by the
photosystems, these organisms rely on an oxygen evolving complex
(mechanism not well understood) that split water into protons,
electrons, and oxygen. The electrons are used to replenish
electrons lost by the photosystems, the protons are used to
generate the proton gradient used to produce ATP, and oxygen, not
used by the plant, leaves as a byproduct.