Which system's primary function is gas exchange?

• A. Digestive System
• B. Respiratory System
• C. Nervous System
• D. Immune System

Answer: (B)

Gas exchange is the main job of the respiratory system. It brings in oxygen from the air into the lungs, where tiny air sacs called alveoli sit surrounded by capillaries. The walls of the alveoli and the capillaries are extremely thin, allowing oxygen to pass into the blood and carbon dioxide to leave the blood to be exhaled. This exchange supplies oxygen for every cell’s energy needs and removes the waste gas, carbon dioxide. The digestive system digests food and absorbs nutrients, the nervous system coordinates actions and signals, and the immune system defends against pathogens. So, the system responsible for swapping gases with the environment is the respiratory system.