English: Structural organization of the antenna system of PSII for red algae and cyanobacteria (A) and energy transfer steps including charge separation (photochemical reaction) at the PSII RC (B) for cyanobacteria. The energy of absorbed photons is passed through a number of antenna molecules [phycoerythrin (absent in most cyanobacteria) → phycocyanin → allophycocyanin] until it reaches the RC Chl a (P680). The excited P680 donates its electron, which is in the excited state of the molecule, to an electron acceptor (A). The electron vacancy of the Chl a is filled by the electron from an electron donor (D). The wavelength numbers (nm) inside the circles represent pigments corresponding to the long wavelength absorption maxima of these pigments.