Reaction centre consists of -

Options

A. single molecule of Chl b
B. LHC
C. single molecule of Chl a
D. single molecule of Chl a but two molecules of Chl b

Answer

To answer the question "Reaction centre consists of -", we need to analyze the components that make up the reaction center in photosynthesis, specifically in Photosystem I (PSI) and Photosystem II (PSII).

### Step-by-Step Solution:

1. **Understanding the Reaction Center**:
- The reaction center is a crucial part of the photosystems in plants where the primary photochemical reactions occur. It is responsible for converting light energy into chemical energy.

2. **Identifying Components of the Reaction Center**:
- The reaction center primarily consists of chlorophyll molecules. Specifically, in Photosystem II, the reaction center is known as P680, and in Photosystem I, it is referred to as P700. These names indicate the wavelengths of light (in nanometers) that these chlorophyll molecules absorb most effectively.

3. **Chlorophyll Types**:
- The main type of chlorophyll found in the reaction center is chlorophyll A. This is the pigment that participates directly in the light reactions of photosynthesis.
- Accessory pigments, such as chlorophyll B and carotenoids, assist in capturing light energy but are not part of the reaction center itself.

4. **Evaluating the Options**:
- **Option A**: A single molecule of chlorophyll B - Incorrect, as chlorophyll B is an accessory pigment and not part of the reaction center.
- **Option B**: Light Harvesting Complex (LHC) - Incorrect, since the LHC contains accessory pigments and does not constitute the reaction center.
- **Option C**: A single molecule of chlorophyll A - Correct, as chlorophyll A is the primary pigment in the reaction center.
- **Option D**: A single molecule of chlorophyll A but 2 molecules of chlorophyll B - Incorrect, as the reaction center does not consist of chlorophyll B.

5. **Conclusion**:
- The correct answer is that the reaction center consists of a single molecule of chlorophyll A.

### Final Answer:
The reaction center consists of a single molecule of chlorophyll A.