What is the relationship between diffusion and concentration gradient?
Particles will diffuse down the concentration gradient until equal concentration is achieved in all areas.
When there is an unequal concentration gradient present in a space the particles will move from the areas of high concentration to the areas of low concentration until the concentration is even throughout the space.
This can also happen across semipermeable membranes where particles such as water can move across the membrane. Water will move by osmosis from the area or side with higher water potential to the area or side with lower water potential until the water potentials become the same. There will still be movement of water across the membrane, but there will be no net movement.
In conclusion, particles will have net movement from high concentration to low concentration until the concentrations are equal. This is why things such as plasmolysis and cytolysis occur, where the concentrations of solutes are different inside and outside of a cell, thus causing extreme net water movement in or out of the cell.