Which mechanism drives gas exchange in the alveoli?

• A. Active transport
• B. Diffusion
• C. Osmosis
• D. Filtration

Answer: (B)

The process driving gas exchange in the alveoli is diffusion. In the context of the respiratory system, diffusion refers to the passive movement of molecules from an area of higher concentration to an area of lower concentration.

In the alveoli, the concentration of oxygen is typically higher than in the blood within the surrounding capillaries, while the concentration of carbon dioxide is higher in the blood than in the alveoli. This concentration gradient facilitates the movement of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli. This exchange occurs rapidly and efficiently due to the thin walls of the alveoli and the large surface area provided by the extensive network of alveolar sacs.

This mechanism is fundamental to respiratory physiology and highlights the efficiency of the body's ability to utilize the principles of diffusion for gas exchange without the need for energy expenditure that would be required in processes like active transport. Other options, such as osmosis, which involves the movement of water, or filtration, which pertains to movement through a porous material or membrane under pressure, do not accurately describe the gas exchange process occurring in the alveoli.