Explain how, during light reaction of photosynthesis, ATP synthesis is chemiosmotic phenomenon

Explanation

a) ATP synthesis in the chloroplast is a chemiosmotic phenomenon.
b) Like.in respiration, in photosynthesis also ATP synthesis is linked to development of proton gradient across the membrane:
c) During splitting of water and also during oxidation of `PQH_(2)` (plastoguinol) protons are released into the lumen of thylakoid.
d) Hence the concentration of protons is many times greater. than that of stroma, thus leading to proton concentration gradient.
Because of the concentration difference the protons - try to move into the stroma, but thylakoids are inpermeable to protons `(H^(+))`.
However an enzyme complex ATPase enzyme is present in the membrane. It allows the movement of `H^(+)` through it into the stroma.
The ATPase enzyme consists of two parts.
1) `F_(0)` is enabeded in the membrane and forms a trans membrane channel that carries out facilitated diffusion of proton through membrane.
2) `F_(2)` , that comes out of the stroma.
The breakdown of the gradient provides enough energy ... to cause a conformational change in the `F_(1)` , particle of the ATPase, which makes enzyme synthesis several molecules of ATP.