Question

What is the significance of proton gradient in photosynthesis?

Answer 1

Part 1: Proton gradient
According to the chemiosmotic hypothesis, the splitting of water in the lumen of thylakoid results in the production of protons. Thus the concentration of protons within the lumen of the thylakoid will be higher than the stroma. This results in a proton gradient.

Part 2: Significance of proton gradient
The proton gradient is essential for ATP synthesis in photosynthesis.
Due to the proton gradient, $H^{+}$ ions move from lumen (high concentration) to stroma (low concentration).
By facilitated diffusion the protons are transported across $F1$- $F_0$ molecules. This movement of protons breaks the proton gradient and results in liberation of energy, which results in a conformational change in the $F_1$ molecule. Thus ATP is produced in the presence of ATP synthase.