Gas exchange of carbon dioxide and oxygen occurs in the ______.

Gas exchange of carbon dioxide and oxygen occurs in the ______.

• A. Trachea
• B. Bronchi
• C. Alveoli
• D. Larynx

Answer: (C)

Gas exchange happens where air meets blood across a very thin, expansive surface: the alveoli. Their walls are only one cell thick and they sit next to a dense network of pulmonary capillaries, so oxygen diffuses from the alveolar air into the blood and carbon dioxide diffuses from the blood into the alveolar space to be exhaled. This process is driven by differences in partial pressures of the gases across the alveolar–capillary membrane. The trachea, bronchi, and larynx are conducting airways that move air in and out but do not participate in gas exchange, because their walls are thicker and they lack the surrounding capillary network needed for diffusion.

Gas exchange happens where air meets blood across a very thin, expansive surface: the alveoli. Their walls are only one cell thick and they sit next to a dense network of pulmonary capillaries, so oxygen diffuses from the alveolar air into the blood and carbon dioxide diffuses from the blood into the alveolar space to be exhaled. This process is driven by differences in partial pressures of the gases across the alveolar–capillary membrane. The trachea, bronchi, and larynx are conducting airways that move air in and out but do not participate in gas exchange, because their walls are thicker and they lack the surrounding capillary network needed for diffusion.