Who discovered the enhancement effect in photosynthesis?

The primary electron acceptor for the electron released by $P_{680}$ in the light reaction is ......... .

Most herbicides attack

Which of the following conditions are favourable for cyclic photophosphorylation?

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 $\text{ATP}$.

The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction?