Which of the following part of respiratory system form exchange part?

Options

A. (1) external nostrils to terminal bronchioles
B. (2) alveoli and their ducts
C. (3) larynx to primary bronchi
D. (4) primary bronchi to terminal bronchioles

Answer

To determine which part of the respiratory system forms the exchange part, we need to understand the pathway of air and where gas exchange occurs.

### Step-by-Step Solution:

1. **Understanding the Respiratory Pathway**:
- The respiratory pathway begins at the nostrils, where air enters the body.

2. **Pathway of Air**:
- From the nostrils, air travels to the nasopharynx.
- It then moves to the trachea, which is the main airway leading to the lungs.

3. **Branching of Airways**:
- The trachea divides into the primary bronchi, which further branch into secondary bronchi and then tertiary bronchioles.
- These bronchioles continue to branch into smaller terminal bronchioles.

4. **Final Destination for Gas Exchange**:
- The terminal bronchioles lead to the alveoli, which are tiny air sacs in the lungs.

5. **Gas Exchange Process**:
- In the alveoli, oxygen from the inhaled air diffuses into the blood capillaries, while carbon dioxide from the blood diffuses into the alveoli to be exhaled.
- This process of gas exchange occurs due to differences in partial pressures of oxygen and carbon dioxide.

6. **Conclusion**:
- The part of the respiratory system where gas exchange occurs is the **alveoli and their ducts**.

### Final Answer:
The part of the respiratory system that forms the exchange part is the **alveoli and their ducts**.