PSII is the membrane protein complex found in oxygenic photosynthetic organisms (higher plants, green algae and cyanobacteria), which harnesses light energy to split water (H2O) into molecular oxygen (O2), protons (H+) and electrons (e- ; reducing equivalents). It drives one of the most oxidising reactions known to occur in nature and is responsible for the production of atmospheric oxygen, essential for aerobic life on this planet. Also, by catalysing the first step of the linear photosynthetic e- transport chain, PSII enables the production of a substantial proportion of the global biomass. A review of its functions may be viewed here.

Interactive view of a higher plant PSII-LHCII complex (based on a single reaction centre, but *structurally a dimer)
Click on the letters of individual PSII subunits to reveal further content: [See also subunit text descriptions here]