What is the role of gas exchange in sustained exercise and how does the diffusion gradient drive it?

• A. Oxygen moves from alveoli to blood and CO2 moves from blood to alveoli; diffusion occurs due to partial pressure gradients.
• B. Oxygen moves from blood to alveoli; CO2 moves from alveoli to blood.
• C. Diffusion is not driven by pressure gradients.
• D. Gas exchange only occurs in the lungs at rest.

Answer: (A)

Gas exchange during sustained exercise serves to provide oxygen to working muscles for energy production and to remove the carbon dioxide produced by metabolism. This relies on diffusion across the respiratory membrane driven by partial pressure differences. Oxygen moves from the alveoli, where its partial pressure is high, into the blood, where it is lower. Carbon dioxide moves from the blood, where its partial pressure is higher, into the alveoli, where it is lower, and is then exhaled. During exercise, increased ventilation and blood flow help keep these gradients favorable, ensuring continued oxygen uptake and CO2 removal as demand rises.