The major limiting factor for photosynthesis is

Options

A. `O_2`
B. Light
C. `CO_2`
D. water

Answer

### Step-by-Step Solution:

1. **Understanding Photosynthesis**: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water, and releasing oxygen as a byproduct.

2. **Identifying Factors Affecting Photosynthesis**: Several factors can limit the rate of photosynthesis, including light intensity, carbon dioxide concentration, water availability, and temperature.

3. **Analyzing Each Option**:
- **Oxygen**: Oxygen is a byproduct of photosynthesis and does not limit the process; therefore, it is not a major limiting factor.
- **Light**: While light is essential for photosynthesis, some plants can thrive in low-light conditions (e.g., shade plants), making it not the primary limiting factor for all plants.
- **Water**: Water is crucial for photosynthesis, but certain plants, like xerophytes, can perform photosynthesis in low water conditions, indicating that water is not universally a major limiting factor.
- **Carbon Dioxide (CO2)**: Carbon dioxide is essential for the photosynthesis process. All plants require CO2 to synthesize glucose, and a lack of CO2 will significantly hinder photosynthesis.

4. **Conclusion**: After evaluating all the factors, it is clear that carbon dioxide is the major limiting factor for photosynthesis across different types of plants.

### Final Answer:
The major limiting factor for photosynthesis is **carbon dioxide (CO2)**.

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