What is the mechanism for gas exchange in the body?

What is the mechanism for gas exchange in the body?

• A. Pressure gradient
• B. Enzyme catalyst
• C. Osmotic pump
• D. Filtration

Answer: (A)

Gas exchange occurs by diffusion driven by a partial pressure gradient across the respiratory membrane. Oxygen moves from the alveoli, where its partial pressure is higher, into the pulmonary capillary blood where it is lower. Carbon dioxide moves in the opposite direction, from blood (higher partial pressure) to alveolar air (lower partial pressure) to be exhaled. This diffusion follows Fick’s law: it scales with surface area, membrane permeability, and the partial pressure difference, and it decreases with greater membrane thickness. The lungs maximize this by having a large surface area of many tiny alveoli and a very thin barrier between air and blood. The other options—enzyme-catalyzed reactions, osmotic pumping, and filtration—do not describe how gas physically moves across the respiratory membranes.

Gas exchange occurs by diffusion driven by a partial pressure gradient across the respiratory membrane. Oxygen moves from the alveoli, where its partial pressure is higher, into the pulmonary capillary blood where it is lower. Carbon dioxide moves in the opposite direction, from blood (higher partial pressure) to alveolar air (lower partial pressure) to be exhaled. This diffusion follows Fick’s law: it scales with surface area, membrane permeability, and the partial pressure difference, and it decreases with greater membrane thickness. The lungs maximize this by having a large surface area of many tiny alveoli and a very thin barrier between air and blood. The other options—enzyme-catalyzed reactions, osmotic pumping, and filtration—do not describe how gas physically moves across the respiratory membranes.