Here's why:

* Concentration Gradient: This refers to the difference in concentration of a substance between two areas.

* Diffusion: The movement of molecules from a region of higher concentration to a region of lower concentration.

Think of it like this:

Imagine a room full of people. If everyone is clustered in one corner (high concentration), they will naturally spread out to fill the rest of the room (lower concentration) over time. This spreading out is diffusion, and it happens because of the difference in concentration.

Key Points:

* Diffusion is a passive process, meaning it doesn't require energy.

* The movement is driven by the random motion of molecules.

* Molecules will always move from an area where they are more concentrated to an area where they are less concentrated, down the concentration gradient.

Let me know if you'd like more details or examples!