Which of the statement about human respiratory system is INCORRECT?

Options

A. Trachea is made up of 16-20 C shaped hyaline cartilaginous rings and is lined by pseudostratified ciliated columnar epithelium.
B. The amount of air which is present in the conducting part of respiratory system is150 ml.
C. The partial pressure of oxygen in inspired air is equal to partial pressure of oxygen in alveolar air.
D. Humans have two pairs of vocal cords out of which only one pair helps in production of sound.

Answer

To determine which statement about the human respiratory system is incorrect, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Trachea is made up of 16 to 20 C-shaped hyaline cartilaginous rings and it is lined by pseudostratified ciliated columnar epithelium.**
- **Analysis:** This statement is correct. The trachea does consist of 16 to 20 C-shaped rings made of hyaline cartilage, which provide structural support. Additionally, the inner lining of the trachea is indeed pseudostratified ciliated columnar epithelium, which helps in trapping and moving particles out of the respiratory tract.

2. **Statement 2: The amount of air which is present in the conducting part of the respiratory system is 150 ml.**
- **Analysis:** This statement is also correct. The volume of air in the conducting zones (known as dead space) is approximately 150 ml. This air does not participate in gas exchange, as it remains in the conducting airways.

3. **Statement 3: The partial pressure of the oxygen in the inspired air is equal to the partial pressure of the oxygen in the alveolar air.**
- **Analysis:** This statement is incorrect. The partial pressure of oxygen in inspired air is higher (around 150-160 mm Hg) compared to the partial pressure of oxygen in alveolar air, which is approximately 104 mm Hg. Therefore, this statement is false.

4. **Statement 4: Humans have two pairs of vocal cords, out of which only one pair helps in the production of sound.**
- **Analysis:** This statement is correct. Humans do have two pairs of vocal cords: true vocal cords (which are responsible for sound production) and false vocal cords (which do not contribute significantly to sound production).

### Conclusion:
The incorrect statement about the human respiratory system is **Statement 3**: "The partial pressure of the oxygen in the inspired air is equal to the partial pressure of the oxygen in the alveolar air."

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