The entire unit is known as a photosytem and in green plants, one finds two of these systems, photosystem I and photosystem II, both of which are involved in the light reactions of photosynthesis. Light energy absorbed by these pigments of the antenna complex is "passed to the reaction center chlorophyll molecules from which it passes along an electron-transport chain" (Blankenship, 215). Photosystems II contains a kind of chlorophyll a (P680) which shows maximum light absorption at a wavelength of about 684 nm. When activated by sunlight, a pair of electrons become excited and leave photosystem II and is replaced by electrons from the photolysis of H2O, summarized as 2H2OO2+4H++4e-.

Molecular oxygen is then released and the protons pass into the lumen (the central space that remains in a cell that has lost its living contents) of the thylakoid (an elongated, flattened fluid-filled sac that forms the basic unit of...
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