What are the modes of exchange of gases `(O_2 and CO_2)` at the level of alveoli and tissue respectively ?

Options

A. Active transport, active transpot
B. Diffusion, diffusion
C. Diffusion, active transport
D. Active transport, diffusion

Answer

To answer the question regarding the modes of exchange of gases (O₂ and CO₂) at the level of alveoli and tissues, we can break down the process into two main parts: external respiration (in the alveoli) and internal respiration (in the tissues).

### Step-by-Step Solution:

1. **Understanding External Respiration (Alveoli)**:
- External respiration refers to the exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries.
- Oxygen (O₂) from the alveoli diffuses into the blood, while carbon dioxide (CO₂) from the blood diffuses into the alveoli.
- This exchange occurs primarily through **simple diffusion** due to the concentration gradient—O₂ is more concentrated in the alveoli than in the blood, and CO₂ is more concentrated in the blood than in the alveoli.

2. **Understanding Internal Respiration (Tissues)**:
- Internal respiration refers to the exchange of gases between the blood and the tissues.
- In the tissues, oxygen (O₂) diffuses from the blood into the cells, while carbon dioxide (CO₂) produced by cellular metabolism diffuses from the cells into the blood.
- Similar to external respiration, this exchange also occurs through **simple diffusion** based on concentration gradients.

3. **Conclusion**:
- Therefore, the modes of gas exchange are:
- **At the level of alveoli**: Simple diffusion (for both O₂ and CO₂).
- **At the level of tissues**: Simple diffusion (for both O₂ and CO₂).

### Final Answer:
- The modes of exchange of gases at the level of alveoli and tissues are both through **simple diffusion**.