Question

Where does cyclic photophosphorylation take place in the leaves ? Why is this process called cyclic? Describe cyclic photophosphorylation.

Answer 1

Cyclic photophosphorylation takes place in chloroplasts in the leaves. It takes place in the stroma lamellae membrane of chloroplasts. The process of cyclic photophosphorylation involves only photosystem I. This process is called cyclic because when only PS I is functional, the electron is circulated within the photosystem and photophosphorylation occurs due to the cyclic flow of electrons. The membrane or lamella of the grana have both PS I and PS II, the stroma lamellae membranes lack PS II as well as NADP reductase enzyme. The excited electron does not pass on to $NAD{P}^{+}$ and is cycled back to the PS I complex through the electron transport chain. Cyclic photophosphorylation is not connected with photolysis of water. Therefore, no oxygen is evolved. It synthesises ATP only. It does not take part in photosynthesis except in certain bacteria.