Mark the incorrect statement

Options

A. Mammals have negative pressure breathing
B. Lecithin keeps alveoli open, speeds up gas exchange and kills bacteria
C. Trachea deliver oxygen directly to the tissue cells
D. A person can expel all the air from lungs by forceful expiration

Answer

To solve the question of marking the incorrect statement, we will analyze each statement one by one and determine if they are true or false.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "Mammals have negative pressure breathing."
- **Explanation**: This statement is true. Mammals use negative pressure breathing, where the volume of the lungs increases, causing a decrease in pressure that allows air to flow in.

2. **Statement 2**: "Lecithin keeps the alveoli open, speeds up the gaseous exchange and kills the bacteria."
- **Explanation**: This statement is also true. Lecithin acts as a surfactant in the lungs, preventing alveolar collapse and facilitating gas exchange.

3. **Statement 3**: "Trachea directly delivers oxygen to tissues and cells."
- **Explanation**: This statement is true but requires context. In insects, the trachea system delivers oxygen directly to cells without the need for blood. However, in mammals, this is not the case, as oxygen is transported by blood.

4. **Statement 4**: "If we do forceful expiration then we can expel all the air from our lungs."
- **Explanation**: This statement is incorrect. Even with forceful expiration, a residual volume of air (approximately 1100-1200 ml) remains in the lungs to prevent collapse.

### Conclusion:
The incorrect statement is **Statement 4**: "If we do forceful expiration then we can expel all the air from our lungs."