Cyclic photophosphorylation produces

What is a reaction centre? Explain.

Assertion $(A) : H^+$ gradient across the thylakoid membrane is essential for the formation of $\text{ATP}$.
Reason $(R) :$ Breakdown of $H^+$ gradient due to the movement of protons through $F_0$ of $\text{ATP}$ synthase releases enough energy to activate $\text{ATP}$ synthase enzyme that catalyses the formation of $\text{ATP}$.

Which is not true regarding cyclic electron transfer system $(ETS)$ in the thylakoid membrane of higher plants?

Chemiosmosis requires:
$I$. $A$ membrane
$II$. $A$ proton pump
$III$. $A$ proton gradient
Select the correct option.

Which is required for chemiosmosis?