For diffusion to occur, there must be a concentration gradient between two regions. This means that there must be a difference in the concentration of particles, such as molecules or ions, in one area compared to another.
When a concentration gradient exists, particles tend to move from an area of higher concentration to an area of lower concentration. This process continues until the concentrations are equalized, leading to a state of equilibrium. Diffusion is a fundamental concept in various fields, including biology, chemistry, and physics, as it explains how substances move across membranes and throughout different environments.