Which of the following statements about the mechanism of ventilation/breathing is incorrect ?

Options

A. As the diaphragm relaxes, air is expelled from the respiratory system.
B. During inspiration the lungs act as suction pump.
C. Inspiration is a passive and expiration is an active process.
D. For quiet breathing, external intercostal muscles and diaphragm play an important role.

Explanation

To determine which statement about the mechanism of ventilation/breathing is incorrect, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Process of Breathing**:
- Breathing consists of two main phases: **inspiration** (inhaling) and **expiration** (exhaling).
- Inspiration involves the intake of air (oxygen) into the lungs, while expiration involves the expulsion of air (carbon dioxide) from the lungs.

2. **Analyzing Each Statement**:
- **Statement 1**: "As the diaphragm relaxes, air is expelled from the respiratory system."
- This statement is **correct**. When the diaphragm relaxes, it returns to its dome shape, decreasing the volume of the thoracic cavity and causing air to be expelled from the lungs.

- **Statement 2**: "During inspiration, the lungs act as the suction pump."
- This statement is also **correct**. During inspiration, the contraction of the diaphragm and intercostal muscles increases the volume of the thoracic cavity, creating a negative pressure that draws air into the lungs.

- **Statement 3**: "Inspiration is a passive and expiration is an active process."
- This statement is **incorrect**. Inspiration is an active process that requires energy for the contraction of respiratory muscles, while expiration is generally a passive process during quiet breathing, relying on the relaxation of these muscles.

- **Statement 4**: "For quiet breathing, external intercostal muscles and diaphragm play an important role."
- This statement is **correct**. The external intercostal muscles and diaphragm are crucial for the process of quiet breathing, facilitating the expansion of the thoracic cavity during inspiration.

3. **Conclusion**:
- The incorrect statement is **Statement 3**: "Inspiration is a passive and expiration is an active process."

### Final Answer:
The incorrect statement about the mechanism of ventilation/breathing is: **Inspiration is a passive and expiration is an active process.**

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