Which describes a primary function of the lungs?

• A. Produce bile
• B. Filter lymph
• C. Helps oxygen enter red blood cells
• D. Regulate blood sugar

Answer: (C)

Gas exchange in the lungs is the primary function. Oxygen from inhaled air moves across the thin walls of the alveoli into the surrounding capillaries and binds to hemoglobin in red blood cells, allowing oxygen to be transported to tissues throughout the body. At the same time, carbon dioxide moves from the blood into the lungs to be exhaled. This oxygen transport is essential for cellular respiration and energy production. The other options describe processes that occur elsewhere: bile production happens in the liver; filtering lymph is a function of the lymphatic system; regulating blood sugar is handled by the pancreas.