Which body system comprises the organs that enable breathing?

• A. Digestive system
• B. Nervous system
• C. Respiratory system
• D. Circulatory system

Answer: (C)

Breathing is enabled by the respiratory system, a group of organs specialized for ventilation and gas exchange. The main components—airways like the trachea and bronchi, the lungs, and the breathing muscles such as the diaphragm—work together to move air in and out and to exchange oxygen and carbon dioxide. Oxygen from the inhaled air passes into the blood in the tiny air sacs of the lungs, while carbon dioxide moves from the blood into the lungs to be exhaled. This system’s primary job is to bring in oxygen and remove carbon dioxide, closely coordinating with the circulatory system to deliver oxygen to tissues throughout the body. Other systems support breathing in various ways—digestion provides energy, the nervous system helps regulate the rate and depth of breathing, and the circulatory system transports gases—but they do not themselves form the organs whose main function is enabling the act of breathing.