Which of the following statements is incorrect ?

To determine which statement is incorrect, let us analyze the process of photophosphorylation in photosynthesis step-by-step:

1. Non-cyclic photophosphorylation (Z-scheme):
This process occurs in the grana lamellae (thylakoid membranes) where both Photosystem I (PS I) and Photosystem II (PS II) are active. Water molecules are split at PS II, and electrons flow through a series of carriers from PS II to PS I, and finally to NADP⁺. During this electron transport, a proton gradient is established across the thylakoid membrane, which drives the synthesis of ATP. At the end of the electron transport chain, NADP⁺ is reduced to NADPH + H⁺. Thus, both ATP and NADPH + H⁺ are synthesized. This makes the statement "Both ATP and NADPH+H⁺ are synthesized during non-cyclic photophosphorylation" correct.

2. Structure and function of Grana and Stroma Lamellae:
The thylakoid membranes are organized into grana (stacked regions) and stroma lamellae (unstacked linking membranes).
- Grana lamellae contain both Photosystem I (PS I) and Photosystem II (PS II). This makes the statement "Grana lamellae have both PS I and PS II" correct.
- Stroma lamellae lack PS II and the enzyme NADP reductase; they possess only PS I. This makes the statement "Stroma lamellae have PS I only and lack NADP reductase" correct.

3. Cyclic photophosphorylation:
Cyclic photophosphorylation occurs only when light of wavelengths beyond 680 nm is available for excitation, or when the stroma lamellae lack PS II and NADP reductase. In this pathway, electrons excited from PS I do not flow to NADP⁺ (due to the lack of NADP reductase and PS II) but are instead cycled back into the electron transport chain (cytochrome b₆f complex) and return to PS I. This cycle drives the synthesis of ATP only. Consequently, cyclic photophosphorylation involves only PS I and does not involve PS II. Therefore, the statement "Cyclic photophosphorylation involves both PS I and PS II" is incorrect.

Thus, the incorrect statement is: "Cyclic photophosphorylation involves both PS I and PS II."