Final answer:
Gas exchange primarily occurs via diffusion, a passive transport mechanism where gas molecules move from higher to lower concentration areas, facilitating oxygen and carbon dioxide exchange in respiration.
Step-by-step explanation:
Gas exchange occurs through a type of passive transport mechanism known as diffusion. This is a process by which gas molecules move from an area of higher concentration to an area of lower concentration without the need for energy from the cell. During physiological respiration, gas exchange involving oxygen (O2) and carbon dioxide (CO2) occurs across the alveolar capillaries and the cells of the lungs. In the lungs, the large surface area of the alveoli and a steep concentration gradient maintained by constant blood flow and breathing facilitate this exchange. Passive diffusion is critical for the oxygenation of blood and the removal of carbon dioxide, ensuring efficient respiration.