The correct sequency of flow of electons in the light reaction is

Options

A. PS II `rarr` Plastoquinone `rarr` Cytochromes `rarr`PS I `rarr` Ferrodoxin
B. PS
I `rarr` Plastoquinone `rarr` Cytochromes `rarr`PS II `rarr` Ferrodoxin
C. PS I `rarr` Ferreodoxin `rarr` PS II `rarr` Cytochromes `rarr` Plastoquinone
D. PS
I `rarr` Plastoquinone `rarr` Cytochromes `rarr` PS II `rarr` Ferrodoxin

Answer

To determine the correct sequence of electron flow during the light reactions of photosynthesis, we can break down the process into clear steps:

### Step-by-Step Solution:

1. **Initiation at Photosystem II (PS2)**:
- The light reaction begins when photons of light are absorbed by chlorophyll molecules in Photosystem II (PS2). This energy excites electrons, which are then released from PS2.

**Hint**: Remember that PS2 is the first photosystem involved in the light reactions.

2. **Water Splitting**:
- To replace the lost electrons in PS2, water molecules are split (photolysis), producing oxygen and releasing electrons. The reaction can be summarized as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]

**Hint**: Water splitting is crucial for replenishing the electrons in PS2.

3. **Electron Transfer to Pheophytin**:
- The excited electrons from PS2 are transferred to an electron acceptor molecule called pheophytin.

**Hint**: Pheophytin acts as the first electron acceptor in the chain.

4. **Transfer to Plastoquinone**:
- From pheophytin, the electrons are passed on to plastoquinone (PQ), which is a mobile electron carrier in the thylakoid membrane.

**Hint**: Think of plastoquinone as a bridge that carries electrons further along the chain.

5. **Cytochrome b6f Complex**:
- The electrons then move to the cytochrome b6f complex, which facilitates the transfer of electrons and also helps in pumping protons into the thylakoid lumen, creating a proton gradient.

**Hint**: The cytochrome b6f complex is essential for creating the proton motive force.

6. **Transfer to Plastocyanin**:
- After passing through the cytochrome b6f complex, the electrons are transferred to plastocyanin (PC), another mobile electron carrier.

**Hint**: Plastocyanin is like a delivery service for electrons to PS1.

7. **Arrival at Photosystem I (PS1)**:
- The electrons are then transferred to Photosystem I (PS1), where they are re-energized by light absorption.

**Hint**: PS1 is the second photosystem and receives electrons from plastocyanin.

8. **Transfer to Ferredoxin**:
- The energized electrons from PS1 are passed to ferredoxin, a small iron-sulfur protein.

**Hint**: Ferredoxin is crucial for the final step of electron transfer.

9. **Formation of NADPH**:
- Finally, ferredoxin transfers the electrons to NADP+, reducing it to NADPH, which is used in the Calvin cycle (dark reactions) for synthesizing glucose.

**Hint**: NADPH is the energy carrier produced in the light reactions.

### Final Sequence of Electron Flow:
The correct sequence of electron flow in the light reactions is:
- PS2 → Pheophytin → Plastoquinone → Cytochrome b6f → Plastocyanin → PS1 → Ferredoxin → NADP+

### Conclusion:
The correct answer to the question regarding the flow of electrons in the light reaction is the first option: **PS2 → Plastoquinone → Cytochrome b6f → Plastocyanin → PS1**.