Select the incorrect statement about photosystems ?

Options

A. PS-I is located toward outerside of thylakoid membrane
B. PS-II is involved in photolysis of water
C. Both PS-II and PS-I participate in cyclic photophosphorylation
D. PS-II requires external electrons in non-cyclic photophosphorylation

Answer

To determine the incorrect statement about photosystems, let's analyze each statement provided in the question step by step.

### Step 1: Understand the Location of Photosystems
- **Statement 1**: PS1 is located towards the outer side of the thylakoidal membrane.
- **Analysis**: This statement is correct. Photosystem I (PS1) is indeed located on the outer side of the thylakoidal membrane, while Photosystem II (PS2) is located towards the inner side.

### Step 2: Role of PS2 in Photolysis
- **Statement 2**: PS2 is involved in the photolysis of water.
- **Analysis**: This statement is also correct. PS2 absorbs light energy, which excites electrons and leads to the photolysis of water, resulting in the release of oxygen and protons.

### Step 3: Participation of Photosystems in Photophosphorylation
- **Statement 3**: Both PS1 and PS2 participate in the photophosphorylation reaction.
- **Analysis**: This statement is incorrect. While both photosystems are involved in the light reactions, only PS1 is involved in cyclic photophosphorylation, while PS2 is involved in non-cyclic photophosphorylation. The cyclic process occurs in the stromal lamellae and involves the recycling of electrons.

### Step 4: Requirement of External Electrons by PS2
- **Statement 4**: PS2 requires external electrons in non-cyclic photophosphorylation.
- **Analysis**: This statement is correct. PS2 does require external electrons, which are provided by the photolysis of water during the non-cyclic photophosphorylation process.

### Conclusion
After analyzing all the statements, the incorrect statement about photosystems is **Statement 3**: "Both PS1 and PS2 participate in the photophosphorylation reaction."

### Final Answer
- The incorrect statement about photosystems is **Statement 3**.

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