Electron donor to `PS` I is

Options

A. Ferredoxin
B. `FeS` centre
C. Plastoquinone
D. Plastocyanin.

Answer

### Step-by-Step Solution:

1. **Identify the Context**: The question asks for the electron donor to Photosystem I (PS I) in the process of photosynthesis.

2. **Understand the Role of Photosystems**: In photosynthesis, there are two main photosystems: Photosystem II (PS II) and Photosystem I (PS I). PS II absorbs light energy and initiates the electron transport chain.

3. **Electron Transport Chain**: After PS II, the electrons are transferred through a series of proteins, including the cytochrome complex. The electron transport chain is crucial for the conversion of light energy into chemical energy.

4. **Identify the Electron Donor**: The electron donor for Photosystem I is **Plastocyanin**. Plastocyanin is a copper-containing protein that acts as an electron transfer agent.

5. **Function of Plastocyanin**: Plastocyanin transfers electrons from the cytochrome complex to Photosystem I, thereby playing a vital role in the electron transport process associated with photosynthesis.

6. **Conclusion**: Therefore, the electron donor to Photosystem I is **Plastocyanin**.