`C_(3)` plants show saturation of photosynthetic reaction at about :-

Options

A. 500 ppm of `CO_(2)`
B. 360 ppm of `CO_(2)`
C. ` gt` 450 ppm of `CO_(2)`
D. 1000 ppm of `CO_(2)`

Answer

To determine the saturation point of photosynthetic reactions in C3 plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photosynthesis**:
- Photosynthesis is the process by which plants synthesize food using light energy, carbon dioxide, and water. The green pigment chlorophyll plays a crucial role in absorbing light.

2. **Identifying Key Components**:
- The main components required for photosynthesis are light, carbon dioxide (CO2), water, and chlorophyll. Among these, carbon dioxide is often considered the limiting factor.

3. **Limiting Factor Concept**:
- A limiting factor is a component that, when in short supply, restricts the rate of a process. In the case of photosynthesis, if carbon dioxide is insufficient, the process will be limited.

4. **Carbon Dioxide Concentration**:
- In the atmosphere, carbon dioxide is present at about 0.03%. Increasing its concentration to around 0.05% can enhance the photosynthetic process.

5. **Saturation Point for C3 Plants**:
- For C3 plants, the saturation point of photosynthesis occurs when the carbon dioxide concentration reaches approximately 450 microlitres per litre (µL/L) or higher. Beyond this concentration, the rate of photosynthesis does not increase significantly.

6. **Comparison with C4 Plants**:
- In contrast, C4 plants reach their saturation point at a lower concentration of carbon dioxide, around 360 µL/L.

### Conclusion:
C3 plants show saturation of photosynthetic reactions at about **450 microlitres per litre (µL/L)** of carbon dioxide concentration or higher.

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