Explanation

The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis. Light energy, an oxygen evolving complex and an electron carrier $Y_{z}$ are required. Electron carrier $Y_{z}$ transfer the released electrons to$P_{680}$. The oxidised$P_{680}$regains its electrons by the photolysis of water into $2H^{+}$, $2e^{-}$and oxygen. Oxygen is given out. $H_{2}O \rightarrow 2H^{+} + \frac{1}{2}O_{2} + 2e^{-}$ Water Proton Electron