The difference in the partial pressures of carbon dioxide is very less at the alveoli of lungs (about 5 mm Hg). Still higher amount of carbon dioxide can diffuse through the diffusion membrane compared to that of Oxygen. The reason is

Options

A. Difference in the partial pressures of oxygen is low at the alveoli of lungs when compared to `CO_2`
B. Solubility of carbon dioxide is 20-25 times higher than that of oxygen.
C. The alveolar membrane is with a single layer of thin squamous epithelium
D. Thin diffusion membrane is favourable for diffusion of gases

Answer

To answer the question regarding why a higher amount of carbon dioxide (CO2) can diffuse through the diffusion membrane compared to oxygen (O2), despite the lower difference in partial pressure of CO2 at the alveoli of the lungs, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Partial Pressure**:
- The partial pressure of a gas is the pressure that gas would exert if it occupied the entire volume alone. In the alveoli, the partial pressure of CO2 is about 5 mm Hg, which is low compared to O2.

2. **Diffusion of Gases**:
- Gases diffuse from areas of higher partial pressure to areas of lower partial pressure. While the partial pressure difference for CO2 is low, it still diffuses effectively.

3. **Comparing Solubility**:
- The key factor here is the solubility of the gases. CO2 is significantly more soluble in blood compared to O2. Specifically, CO2 is 20 to 25 times more soluble than O2.

4. **Effect of Solubility on Diffusion**:
- Because CO2 is more soluble, it can diffuse across the alveolar membrane more readily, even when its partial pressure difference is lower than that of O2.

5. **Conclusion**:
- Therefore, the reason that a higher amount of CO2 can diffuse through the diffusion membrane compared to O2, despite the lower partial pressure difference, is due to the much higher solubility of CO2 in comparison to O2.

### Final Answer:
The reason is that the solubility of carbon dioxide (CO2) is 20 to 25 times higher than that of oxygen (O2), allowing CO2 to diffuse more effectively despite its lower partial pressure difference in the alveoli.

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