Which of the following is NOT an organ of the respiratory system?

The diaphragm is primarily a muscle rather than an organ of the respiratory system. While it plays a crucial role in respiration—contracting to expand the thoracic cavity and facilitate inhalation—it does not function as a gas exchange organ or a pathway for air like the lungs, trachea, or pharynx do.

In contrast, the lungs are the primary organs for gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled. The trachea serves as a main airway that conducts air from the larynx to the bronchi, leading into the lungs. The pharynx acts as a passageway for air and food, connecting the nose and mouth to the larynx and esophagus, but it is also integral to the respiratory process.

Thus, identifying the diaphragm as not being considered an organ of the respiratory system highlights its functional distinction as a muscle involved in the respiratory mechanics, rather than a structural organ engaged in the processes of respiration itself.