Which of the following statements about the human respiratory system are INCORRECT ?
I. During swallowing , glottis can covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx.
II. The trachea is a straight tube extending up to the mid- thoracic cavity, which divides at the level of the fourth thoracic vertebra into a right and left primary bronchi.
III. The trachea , primary secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings made up of hyaline cartilage.
IV. The respiratory part transports the atmospheric air to the alveoli, clear it from foreign particles, humidifies and also brings the air to body temperature.

Options

A. I and III
B. II and IV
C. I and II
D. II,III and IV

Answer

To determine which statements about the human respiratory system are incorrect, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "During swallowing, glottis can be covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx."
- **Analysis**: This statement is correct. The epiglottis is indeed a flap that covers the glottis during swallowing to prevent food from entering the larynx.

2. **Statement II**: "The trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of the fourth thoracic vertebra into a right and left primary bronchi."
- **Analysis**: This statement is incorrect. The trachea divides into the right and left primary bronchi at the level of the **fifth thoracic vertebra**, not the fourth.

3. **Statement III**: "The trachea, primary, secondary, and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings made up of hyaline cartilage."
- **Analysis**: This statement is correct. The trachea and bronchi are supported by C-shaped rings of hyaline cartilage which provide structural support.

4. **Statement IV**: "The respiratory part transports the atmospheric air to the alveoli, clears it from foreign particles, humidifies, and also brings the air to body temperature."
- **Analysis**: This statement is incorrect. The **conducting part** of the respiratory system (which includes the trachea and bronchi) is responsible for transporting air to the alveoli and conditioning it (clearing, humidifying, and warming). The respiratory part primarily refers to the alveoli where gas exchange occurs.

### Conclusion:
The incorrect statements are:
- **Statement II** (incorrect about the division of the trachea)
- **Statement IV** (incorrect about the function of the respiratory part)

### Final Answer:
The incorrect statements about the human respiratory system are **II and IV**.