If there were no pollution by humans the concentration of carbon dioxide in the atmosphser would reletively constant because

Options

A. in photoautorophs the rate of photosynthesis is equal to the rate of their cellular respiration
B. in plants photosynthesis occurs during the day and cellualr respiration at night
C. during photosynthesis carbon dioxide is consumed and oxygen gas is released
D. the rate of photosynthsis by photoaurtotrophs is roughly equal to the rate of cellular respiration by all organisms

Answer

To answer the question, "If there were no pollution by humans, the concentration of carbon dioxide in the atmosphere would be relatively constant because," we can analyze the options provided and arrive at a conclusion step by step.

### Step-by-Step Solution:

1. **Understanding Photosynthesis and Respiration**:
- Photosynthesis is the process by which photoautotrophs (like plants) convert carbon dioxide (CO2) and water into glucose and oxygen using sunlight.
- Cellular respiration is the process by which all organisms, including plants, convert glucose and oxygen back into carbon dioxide, water, and energy.

2. **Analyzing the Role of Photoautotrophs**:
- In a balanced ecosystem, the rate of photosynthesis by photoautotrophs should ideally match the rate of respiration by all organisms. This means that the CO2 consumed during photosynthesis is roughly equal to the CO2 released during respiration.

3. **Considering Other Organisms**:
- While photoautotrophs are crucial for photosynthesis, other organisms (like heterotrophs, saprotrophs, etc.) also contribute to the carbon cycle through respiration. Thus, it is essential to consider the respiration of all living organisms when discussing CO2 levels.

4. **Evaluating the Options**:
- **Option 1**: States that the rate of photosynthesis is equal to the rate of cellular respiration in photoautotrophs. This is partially true but does not account for all organisms, making it an incomplete answer.
- **Option 2**: Suggests that photosynthesis occurs during the day and respiration at night. This does not explain how CO2 levels remain constant, so it is incorrect.
- **Option 3**: States that during photosynthesis, CO2 is consumed and oxygen is released. While true, this does not explain the constancy of CO2 levels.
- **Option 4**: Claims that the rate of photosynthesis by photoautotrophs is roughly equal to the rate of cellular respiration by all organisms. This option accurately reflects the balance needed to maintain a relatively constant concentration of CO2 in the atmosphere.

5. **Conclusion**:
- Therefore, the correct answer is **Option 4**: The rate of photosynthesis by photoautotrophs is roughly equal to the rate of cellular respiration by all organisms, which helps maintain a relatively constant concentration of carbon dioxide in the atmosphere.