Identify the correct sequence of flow of electrons in the light reaction.

Options

A. PS I, plasotquinone, cytochromes, PS II, ferredoxin
B. PS I, ferredoxin, PS II
C. PS I, plastoquinone, cytochromes
D. PS II, plastoquinone, cytochromes, PS I, ferredoxin

Answer

To identify the correct sequence of flow of electrons in the light reaction of photosynthesis, we can break down the process step by step:

### Step-by-Step Solution:

1. **Start with Photosystem II (PSII)**: The light reaction begins when light energy is absorbed by chlorophyll molecules in Photosystem II (PSII). This energy excites electrons, which are then released from PSII.

2. **Electron Transfer to Plastoquinone (PQ)**: The excited electrons from PSII are transferred to a molecule called Plastoquinone (PQ). PQ acts as an electron carrier in the electron transport chain.

3. **Transfer to Cytochrome b6f Complex**: After PQ, the electrons are passed to the Cytochrome b6f complex. This complex is crucial for transferring electrons further down the chain and also helps in pumping protons into the thylakoid lumen.

4. **Electron Flow to Photosystem I (PSI)**: The electrons then flow from the Cytochrome b6f complex to Photosystem I (PSI). Here, PSI absorbs light energy, which further excites the electrons.

5. **Transfer to Ferredoxin (FD)**: After being energized in PSI, the electrons are transferred to Ferredoxin (FD), a small iron-sulfur protein that acts as an electron carrier.

6. **Formation of NADPH**: Finally, the electrons from Ferredoxin are used to reduce NADP+ to NADPH, which is an important energy carrier used in the Calvin cycle.

### Correct Sequence:
The correct sequence of the flow of electrons in the light reaction is:
1. Photosystem II (PSII)
2. Plastoquinone (PQ)
3. Cytochrome b6f complex
4. Photosystem I (PSI)
5. Ferredoxin (FD)
6. NADP+ to NADPH

### Final Answer:
The correct sequence of flow of electrons in the light reaction is:
**Photosystem II → Plastoquinone → Cytochrome b6f → Photosystem I → Ferredoxin → NADPH**

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