Question

The element essential for evolution of oxygen during photosynthesis is

• A. Mg
• B. Mn
• C. Fe
• D. Mo

Answer 1

Answer: (B)

Manganese $(Mn)$ is a microelement and is a component of oxygen evolving complex. The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis or photocatalytic splitting of water. Light energy, an oxygen evolving complex $(OEC)$ and an electron carrier $Y_z$ are required. Oxygen evolving complex is attached to the inner surface of thylakoid membrane. The enzyme has four $Mn$ ions. Light energised changes in
$Mn\left(M{n}^{2+},M{n}^{3+},M{n}^{4+}\right)$ removes electrons from $O{H}^{-}$ component of water forming oxygen. Liberation of $O_2$ also requires two other ions, $C{a}^{2+}$ and $C{l}^{-}$.
$4O{H}^{-}\underset{M{n}^{2+},C{a}^{2+},C{l}^{-}}{\overset{\text{ oxygen evolving complex }}{\to }}2H_{2}O+O_2\uparrow +4e^{-}$