(a) The reaction takes place in reaction centre PS II, located on the inner surface of thylakoid membrane. It is known as water splitting centre where electrons are extracted from water. The $\mathrm{Mn}^{+}$and $\mathrm{Cl}^{-}$ions catalyse this reaction.

(b) Splitting of water is an important event in photosynthesis as

(i) It releases molecular oxygen as byproduct of photosynthesis and is the significant source of oxygen in air, or is essential for all living beings on earth.

(ii) Hydrogen ions produced, are utilised in reducing NADP to NADPH, a strong reducing agent.

(iii) The electrons released are transferred from PS II to PS I through a series of electron carriers thus, creating a gradient for the synthesis of ATP.

The cyanobacteria and photosynthetic bacteria are prokaryotes. They do not have well defined membrane bound cell organelles, but these organisms have photosynthetic pigments in a membranous form, which are primitive in nature but can trap and use solar energy. So, they can carry out photosynthesis.

(a) NADP reductase enzyme is located on the outer side of thylakoid membrane. It is bounded to the thylakoid membrance in light and becomes free in stroma during dark.

(b) ATP Molecules The movement of $\mathrm{H}^{+}$ions across the membrane is coupled with the formation of ATP synthesis in presence of enzyme ATP synthase.

The girdling experiment cannot be done in monocots. The monocot stem has vascular bundles scattered all over the width of stem so, we cannot reach that specific band of the phloem tissues as we get in dicots.

(a) 2 molecules of ATP for phosphorylation and two molecules of NADPH for reduction are required per $\mathrm{CO}_2$ molecule fixed.

(b) The calvin cycle occurs in the stroma of the chloroplast.