What is the primary role of the respiratory system?

• A. Filters pathogens from blood
• B. Produces digestive enzymes
• C. Regulates blood sugar
• D. Facilitates gas exchange in lungs

Answer: (D)

Gas exchange is the main function of the respiratory system. It brings in oxygen from the air and removes carbon dioxide, a waste product of metabolism. This exchange happens mainly in the lungs’ tiny air sacs called alveoli, where oxygen passes into the blood and carbon dioxide moves from the blood into the air to be exhaled. Without this process, cells wouldn’t get the oxygen they need to produce energy, and carbon dioxide would build up to harmful levels. The other options relate to different body systems: filtering pathogens from blood is an immune/blood-cleansing function, producing digestive enzymes belongs to the digestive system, and regulating blood sugar is an endocrine/metabolic function.