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

• A. Heart
• B. Nasal cavities
• C. Alveoli
• D. Larynx

Answer: (A)

The main idea here is distinguishing which structures are part of the respiratory system versus other body systems. The respiratory system includes structures that bring in air and exchange gases: the nasal cavities filter and warm air as it enters, the larynx guides air to the lower airways, and the alveoli are the tiny sacs where oxygen enters blood and carbon dioxide is released. The heart, on the other hand, belongs to the circulatory system and pumps blood to carry gases to and from tissues. Since the heart is not a respiratory organ, it is the correct choice.