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 the provided statements one by one.

### Step 1: Analyze the first statement about the trachea.
The first statement mentions that the trachea has 16 to 20 C-shaped hyaline cartilage rings and is lined with pseudostratified ciliated columnar epithelium.

- **Correctness**: This statement is correct. The trachea does indeed have 16 to 20 C-shaped cartilage rings that provide structural support and prevent collapse. The lining of the trachea is made up of pseudostratified ciliated columnar epithelium, which helps in trapping and moving particles out of the respiratory tract.

### Step 2: Analyze the second statement regarding the conducting part of the respiratory system.
The second statement claims that there is approximately 150 ml of air present in the conducting part of the respiratory system.

- **Correctness**: This statement is also correct. The conducting part of the respiratory system, which includes the trachea and bronchi, indeed holds about 150 ml of air, which is known as the anatomical dead space where no gas exchange occurs.

### Step 3: Analyze the third statement about the partial pressure of oxygen.
The third statement asserts that in inspired air and alveolar air, the pressure of oxygen is equal.

- **Correctness**: This statement is incorrect. The partial pressure of oxygen in inspired air is approximately 159 mmHg, while in alveolar air, it is about 104 mmHg. For gas exchange to occur, there must be a difference in the partial pressures (concentration gradient) of oxygen between the inspired air and the alveolar air. If they were equal, there would be no movement of oxygen into the blood.

### Step 4: Analyze the fourth statement regarding vocal cords.
The fourth statement states that human beings have two pairs of vocal cords, only one of which helps in the production of sound.

- **Correctness**: This statement is correct. Humans have two pairs of vocal cords: the true vocal cords (which are involved in sound production) and the false vocal cords (which do not contribute to sound but can assist in protecting the airway).

### Conclusion:
Based on the analysis, the incorrect statement is the third one, which claims that the partial pressure of oxygen is equal in inspired air and alveolar air.

### Final Answer:
The incorrect statement about the human respiratory system is: "In inspired air and alveolar air, the pressure of oxygen is equal."

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