Question

Chemiosmotic hypothesis is related to

• A. photolysis of water
• B. synthesis of ATP
• C. conversion of NADP+ to NADPH
• D. osmoregulation of ions

Answer 1

The correct option is B synthesis of ATP

Chemiosmotic hypothesis was proposed by Mitchell to explain the synthesis of ATP. Chemiosmosis involves the movement of ions across a biological membrane along the concentration gradient and it helps in the synthesis of ATP.

During the light dependent reactions of photosynthesis, there is an accumulation of protons inside the lumen of thylakoids. The number of protons is high inside the lumen of thylakoids when compared to the stroma of chloroplast. This creates a proton gradient and the breakdown of this gradient generates ATP. The gradient is broken down due to the movement of protons across the membrane into the stroma through ATP synthase.

The chloroplast ATP synthase has two parts: $C{F}_0$ located in the thylakoid membrane and $C{F}_1$ that protrudes on the outer surface of the thylakoid membrane facing the stroma. The $C{F}_0$ forms a transmembrane channel for the movement of protons due to which energy is released and that causes conformational changes in the $C{F}_1$ of the enzyme. Utilising this energy, ATP is synthesised from ADP by the enzyme ATP synthase.