With reference to factors affecting the rate of Photosynthesis, which of the following statements is `ul("not")` correct ?

Options

A. Light saturation for `CO_2` fixation occurs at 10% full sunlight .
B. Increasing atmosphere `CO_2` concentration up to 0.05% can enhance `CO_2` fixation rate
C. `C_3` plants respond 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, let's analyze each option step by step.

### Step 1: Analyze the Options
1. **Option 1**: "Light saturation of CO2 fixation occurs at 8% full sunlight."
- This statement suggests that CO2 fixation reaches its maximum rate at 8% of full sunlight. This is a plausible statement as light saturation can occur at lower light intensities for certain plants.

2. **Option 2**: "Increasing atmospheric CO2 concentration up to 0.5% can enhance CO2 fixation rate."
- This statement indicates that higher CO2 concentrations can enhance the rate of photosynthesis. This is generally true, as CO2 is a key substrate for photosynthesis.

3. **Option 3**: "C3 plants respond to higher temperatures with enhanced photosynthesis while C4 plants have much lower temperature optimum."
- This statement is incorrect. C3 plants typically experience decreased photosynthesis at higher temperatures due to increased photorespiration. In contrast, C4 plants are adapted to thrive at higher temperatures.

4. **Option 4**: "Tomato is a greenhouse crop which can be grown in CO2 enriched atmosphere for higher yield."
- This statement is correct. Growing tomatoes in a CO2 enriched atmosphere can indeed enhance their yield.

### Step 2: Identify the Incorrect Statement
From the analysis, **Option 3** is the incorrect statement. C3 plants do not enhance photosynthesis at higher temperatures; instead, their photosynthesis decreases due to increased photorespiration.

### Conclusion
The statement that is not correct regarding the factors affecting the rate of photosynthesis is **Option 3**.

---