NEET UG 2011 — Botany Mineral Nutrition

Photolysis of water requires light energy, and oxygen evolving complex (OEC) and an electron carrier $Y_z$Yz​. OEC complex was formerly called Z-enzyme. It has four Mn ions. Light energy brings about changes in $\mathrm{Mn}\left(\mathrm{Mn}^{+2}, \mathrm{Mn}^{+3}, \mathrm{Mn}^{+4}\right)$Mn(Mn+2,Mn+3,Mn+4) which helps in removing electrons from $\mathrm{OH}^{-}$OH− component of water forming oxygen. Liberation of oxygen also requires $\mathrm{Cl}^{-}$Cl−and $\mathrm{Ca}^{2+}$Ca2+.