Answer:
Diffusion
Step-by-step explanation:
Diffusion can be defined as the movement of molecules from a region of higher concentration to a region of lower concentration. Diffusion tends to occur when gases move randomly from one place to another.
Diffusion helps in the exchange of gases between the blood and the lungs because the air present in the lungs have a high concentration of oxygen than that of the blood which has a lower concentration. This concentration gradient makes it possible for gas to be exchanged during respiration.