Diffusion is the net (overall) movement of particles from an area of high concentration to an area of lower concentration.
When you put a drop of red dye into a glass of water, the dye diffuses until it is at equal concentration everywhere in solution.
A difference in concentration of a particle between two areas is called a concentration gradient. Diffusion occurs down a concentration gradient.
Diffusion is a passive process; it does not require energy.
Diffusion is fundamental to how organisms function:
- Proteins diffuse within the cytoplasm of cells.
- Carbon dioxide diffuses from the air into cells in the leaf for photosynthesis.
- Oxygen diffuses from the blood into tissues for respiration.
Organisms can control concentration gradients to determine the direction of diffusion.