How many of the given statements is/are correct for cyclic phosphorylation?
(I) Only PS I is functional.
(II) Occurs is stroma lamellae.
(III) Occurs when only light of wavelength less than 680 nm is available for excitation.
(IV) Synthesis of both ATP and NADPH occurs.
(V) Electrons are circulated within the photosystem.

(I) Only PS I is functional: This statement is correct. During cyclic phosphorylation, only Photosystem I (PS I) is involved, as it can produce ATP through cyclic electron flow.

(II) Occurs in stroma lamellae: This statement is correct. Cyclic phosphorylation occurs in the stroma lamellae.

(III) Occurs when only light of wavelength less than 680 nm is available for excitation: This statement is incorrect. Cyclic phosphorylation can occur when only light of wavelength greater than 680 nm is available for excitation. PS I absorbs light of longer wavelengths (around 700 nm) and can carry out cyclic electron flow in such conditions.

(IV) Synthesis of both ATP and NADPH occurs: This statement is incorrect. During cyclic phosphorylation, only ATP synthesis occurs. NADPH is not produced because the electrons do not flow to NADP reductase enzyme, instead, they are cycled back to the electron transport chain of PS I.

(V) Electrons are circulated within the photosystem: This statement is correct. During cyclic phosphorylation, electrons released from Photosystem I are circulated within the photosystem, from the primary electron acceptor of PS I back to PS I itself, through an electron transport chain. This cyclic flow of electrons generates a proton gradient, which is used to produce ATP through ATP synthase.