With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct ?

Options

A. Light saturation for `CO_(2)` fixation occurs at 10% of full sunlight.
B. Increasing atmospheric `CO_(2)` concentration up to 0.05% can enhance `CO_(2)` fixation rate.
C. `C_(3)` plants responds to higher temperatures with enhanced photosynthesis while `C_(4)` plants have much lower temperature optimum.
D. Tomato is a greenhouse crop which can be grown in `CO_(2)`- enriched atmosphere for higher yield.

Answer

To determine which statement is not correct regarding the factors affecting the rate of photosynthesis, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Light Saturation for Carbon Dioxide Fixation**:
- The first statement mentions that light saturation for carbon dioxide fixation occurs at 10% full sunlight.
- In general, many plants can achieve saturation at lower light intensities, but 10% full sunlight is considered a reasonable estimate for many plants. This statement is likely correct.

2. **Increasing Atmospheric Carbon Dioxide Concentration**:
- The second statement discusses that increasing atmospheric carbon dioxide concentration up to 0.5% can enhance the carbon dioxide fixation rate.
- This is true; higher concentrations of CO2 can increase the rate of photosynthesis until other factors become limiting.

3. **C3 and C4 Plants Temperature Response**:
- The third statement claims that C3 plants respond to higher temperatures with enhanced photosynthesis, while C4 plants have a much lower temperature optimum.
- This statement is incorrect. C3 plants generally have an optimum temperature range and can suffer from reduced photosynthetic efficiency at high temperatures due to enzyme denaturation and photorespiration. In contrast, C4 plants are more efficient at higher temperatures.

4. **Tomato as a Greenhouse Crop**:
- The fourth statement indicates that tomato is a greenhouse crop that can be grown in a carbon dioxide enriched atmosphere for higher yields.
- This statement is correct; tomatoes can benefit from increased CO2 levels, which can enhance their growth and yield.

### Conclusion:
Based on the analysis, the statement that is not correct is **option C**, which suggests that C3 plants respond positively to higher temperatures.

### Final Answer:
**Option C** is the statement that is not correct.

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