Which of the following is an organ of the respiratory system?

• A. Nasal cavities
• B. Heart
• C. Liver
• D. Brain

Answer: (A)

The respiratory system includes structures that conduct air and prepare it for gas exchange, and the nasal cavities are the entryway for inhaled air. They filter out particles with nasal hairs and mucus, warm and humidify the air, and move it toward the throat and lungs, helping protect the delicate tissues of the lower airways and optimize conditions for gas exchange in the lungs. While the lungs handle oxygen uptake and carbon dioxide release, the nasal cavities cradle air before it reaches them. The heart, liver, and brain have roles in circulation, metabolism, and control, but they are not part of the respiratory tract.