Correct sequence of involvement of the following in noncyclic electron transport
(i) `PC` (ii) `PQ` (iii) `Pheo` (iv) `Fd`

Options

A. `ii, i, iii, iv`
B. `iii, ii, iv, i`
C. `iv, i, ii, iii`
D. `iii, ii, i, iv`.

Answer

To determine the correct sequence of involvement of the components in noncyclic electron transport during photosynthesis, we need to understand the order in which these components participate in the process. The components mentioned are:

1. **PC** (Plastocyanin)
2. **PQ** (Plastoquinone)
3. **Pheo** (Pheophytin)
4. **Fd** (Ferredoxin)

### Step-by-Step Solution:

1. **Initiation of Noncyclic Electron Transport**:
- The process begins when light energy is absorbed by chlorophyll in **Photosystem II (PSII)**. This energy excites electrons, leading to the photolysis of water, which releases electrons.

2. **First Electron Acceptor**:
- The first electron acceptor from **Photosystem II** is **Pheophytin (Pheo)**. It captures the excited electrons from chlorophyll after they are released due to the absorption of light energy.

3. **Transfer to Plastoquinone**:
- After being accepted by Pheophytin, the electrons are transferred to **Plastoquinone (PQ)**. This component acts as an electron carrier, moving the electrons further along the electron transport chain.

4. **Transfer to Plastocyanin**:
- The electrons are then passed from Plastoquinone to the **B6F complex**, which facilitates the transfer to **Plastocyanin (PC)**. Plastocyanin is another electron carrier that transports electrons to Photosystem I (PSI).

5. **Transfer to Ferredoxin**:
- Finally, after the electrons are re-excited in **Photosystem I**, they are transferred to **Ferredoxin (Fd)**, which is the last component in this sequence before the electrons are used to reduce NADP+ to NADPH.

### Correct Sequence:
Based on the above steps, the correct sequence of involvement in noncyclic electron transport is:
- **Pheophytin (Pheo)** → **Plastoquinone (PQ)** → **Plastocyanin (PC)** → **Ferredoxin (Fd)**.

### Final Answer:
The correct order is: **(iii) Pheo → (ii) PQ → (i) PC → (iv) Fd**.