<P> The excitation P680 → P680 of the reaction center pigment P680 occurs here . These special chlorophyll molecules embedded in PS II absorb the energy of photons, with maximal absorption at 680 nm . Electrons within these molecules are promoted to a higher - energy state . This is one of two core processes in photosynthesis, and it occurs with astonishing efficiency (greater than 90%) because, in addition to direct excitation by light at 680 nm, the energy of light first harvested by antenna proteins at other wavelengths in the light - harvesting system is also transferred to these special chlorophyll molecules . </P> <P> This is followed by the step P680 → pheophytin, and then on to plastoquinone, which occurs within the reaction center of PS II . High - energy electrons are transferred to plastoquinone before it subsequently picks up two protons to become plastoquinol . Plastoquinol is then released into the membrane as a mobile electron carrier . </P> <P> This is the second core process in photosynthesis . The initial stages occur within picoseconds, with an efficiency of 100% . The seemingly impossible efficiency is due to the precise positioning of molecules within the reaction center . This is a solid - state process, not a chemical reaction . It occurs within an essentially crystalline environment created by the macromolecular structure of PS II . The usual rules of chemistry (which involve random collisions and random energy distributions) do not apply in solid - state environments . </P> <P> When the chlorophyll passes the electron to pheophytin, it obtains an electron from P. In turn, P can oxidize the Z (or Y) molecule . Once oxidized, the Z molecule can derive electrons from the oxygen - evolving complex (OEC). Dolai's S - state diagrams show the reactions of water splitting in the oxygen - evolving complex . </P>

Where do electrons from photosystem 1 and 2 end up