P680 1747500 192925681 2008-02-21T00:22:51Z 69.232.225.191 {{Unreferenced|date=June 2007}} '''P680''', or ''Photosystem II'', (where P stands for photosystem) is the [[Photosynthetic reaction center|reaction-center]] associated with [[photosystem II]] and consists of 2 [[chlorophyll|chlorophyll ''a'']] molecules that are not bound to proteins unlike the other chlorophyll molecules in photosystem II. Its [[absorption spectrum]] peaks at 680 nm, which is in the red part of the spectrum. When photosystem II absorbs light, an electron is excited to a higher [[energy level]]. This electron drops down to its ground state level and releases energy, which is then transmitted through a [[light-harvesting complex]] (LHCII) until it reaches a P680 chlorophyll and excites an electron on the P680 molecule. The resulting P680 with excited electron is designated P680*. The electron is subsequently captured by the primary electron acceptor. To replace the electron water will be oxidized in the [[Oxygen evolving complex]]. P680 is the strongest biological oxidizing agent known. ==See also== *[[P700]]. [[Category:photosynthesis]] [[Category:light reactions]] {{biochem-stub}} [[de:P680]]