Select the correct statements about `CO_(2)` in photosynthesis :

Options

A. Rate of photosynthesis decreases with increase in `CO_(2)` conc. upto 0.50%
B. Green house crops (`C_(3)` plants) show `CO_(2)` fertilization effect
C. Atmospheric `CO_(2)` is rarely limiting factor for `C_(3)` plants
D. High conc. of `CO_(2)` in `C_(3)` plants causes photorespiration

Answer

To solve the question regarding the correct statements about carbon dioxide (CO₂) in photosynthesis, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Rate of photosynthesis decreases with increase in carbon dioxide concentration up to 0.50%.**
- **Analysis:** This statement is false. The rate of photosynthesis actually increases with an increase in carbon dioxide concentration up to a certain point (around 0.50%). Beyond this point, excessive CO₂ can be harmful to plants.
- **Conclusion:** This statement is incorrect.

2. **Statement 2: Greenhouse crops C3 plants show carbon dioxide fertilization effect.**
- **Analysis:** This statement is true. C3 plants, such as tomatoes, thrive in environments with higher carbon dioxide concentrations, which enhances their growth. This is known as the carbon dioxide fertilization effect.
- **Conclusion:** This statement is correct.

3. **Statement 3: Atmospheric carbon dioxide is a limiting factor for C3 plants.**
- **Analysis:** This statement is false. While CO₂ can be a limiting factor, C3 plants are more efficient at utilizing CO₂ at higher concentrations. Therefore, atmospheric CO₂ is not typically a limiting factor for these plants.
- **Conclusion:** This statement is incorrect.

4. **Statement 4: High concentration of carbon dioxide in C3 plants causes photorespiration.**
- **Analysis:** This statement is false. Photorespiration occurs primarily under low CO₂ concentrations. High CO₂ levels actually help to minimize photorespiration in C3 plants.
- **Conclusion:** This statement is incorrect.

### Final Answer:
The only correct statement about CO₂ in photosynthesis is **Statement 2**: Greenhouse crops C3 plants show carbon dioxide fertilization effect.

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