Which portion of the respiratory system has little to no gas exchange because it lacks alveoli?

• A. Alveoli
• B. Dead space
• C. Diffusion
• D. Ventilation

Answer: (B)

Gas exchange happens where there are alveoli, because oxygen and carbon dioxide diffuse across the thin alveolar membranes. The portion with little to no gas exchange is the anatomical dead space—the airways that conduct air (like the trachea and bronchi) but lack alveoli. They fill with air each breath, but this air doesn’t participate in gas exchange. In contrast, alveoli are the actual sites of gas exchange; diffusion is the process by which gases move across the alveolar-capillary membrane, and ventilation refers to moving air in and out of the lungs.