Following steps in random order are given below for photophsophorylation through chemiosmosis
I ATP synthase produces ATP due to flow of `H^(+)` form thylakoid lumen to stroma
II NADP reductase located on stroma side of membrane obtains `e^(-)` froms PSI and protons from stroma to form `NADPH_(2)`
IIICyotchrome system (B&F) transport electrons and pumps `H^(+)` form stroma to thylakoid space
IV PSII oxidises water
V Reaction centre of PSII gets photoecited having released electrons

Options

A. I,II,III,IV,V
B. V.IV,III,II,I
C. I,III,II,IV,V
D. III,V,IV,II,I

Answer

To solve the question regarding the correct order of steps in photophosphorylation through chemiosmosis, let's analyze the steps provided and arrange them logically based on the process of photosynthesis in higher plants.

### Step-by-Step Solution:

1. **Step V: Reaction centre of PSII gets photoexcited, having released electrons.**
- This is the initial step where light energy excites the electrons in the reaction center of Photosystem II (PSII), leading to the release of these electrons.

2. **Step IV: PSII oxidizes water.**
- To replace the lost electrons from PSII, water molecules are split (photolysis), releasing oxygen and protons. This step occurs right after the excitation of electrons.

3. **Step III: Cytochrome system (B&F) transports electrons and pumps H⁺ from stroma to thylakoid space.**
- The electrons released from PSII are transferred through the electron transport chain, including the cytochrome system, which also pumps protons into the thylakoid lumen, creating a proton gradient.

4. **Step II: NADP reductase located on the stroma side of the membrane obtains e⁻ from PSI and protons from stroma to form NADPH₂.**
- After the electrons travel through the electron transport chain, they reach Photosystem I (PSI), where they are re-excited by light. The electrons are then transferred to NADP⁺ along with protons from the stroma to form NADPH₂.

5. **Step I: ATP synthase produces ATP due to the flow of H⁺ from thylakoid lumen to stroma.**
- The proton gradient created by the pumping of protons into the thylakoid lumen drives ATP synthase, which synthesizes ATP as protons flow back into the stroma.

### Final Order of Steps:
The correct order of steps for photophosphorylation through chemiosmosis is:
- V → IV → III → II → I