Particles in a liquid and a gas move continuously. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas.
It is important to remember that the particles:
If a crystal of a coloured chemical, eg potassium manganate(VII), is placed in water, the particles spread out and mix with the water particles. The process is:
The particles have moved from a region of high concentration in the crystal to a low concentration in the water. This difference in concentration is called a concentration gradient. Particles will move down a concentration gradient, from a high concentration to a low concentration.
As well as diffusion occurring between different regions, it also occurs across membranes, between the outside and inside of cells.
Some substances move into and out of living cells by diffusion.
In a leaf:
In the lungs:
In liver cells: