Which part of the respiratory system serves as the passageway for air?

• A. Left primary bronchus
• B. Parietal pleurae
• C. Right middle lobe
• D. Cavity pleura

Answer: (A)

The left primary bronchus serves as a crucial passageway for air, directing it from the trachea into the left lung. As one of the two main bronchi, it branches off from the trachea, allowing air to enter the lung where it can be distributed to the bronchial tree and ultimately reach the alveoli for gas exchange. This structure is vital for the respiratory process, as it plays an essential role in ensuring that oxygen is delivered to the lungs and that carbon dioxide is expelled from the body.

The parietal pleurae are membranes lining the thoracic cavity, not directly involved in the transport of air but rather in providing lubrication and protection for the lungs. The right middle lobe is part of the lung itself, where gas exchange occurs, rather than a passageway for air. Similarly, the cavity pleura refers to the space between the pleural membranes and does not function as a conduit for respiratory airflow.