Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.
Diffusion happens in liquids and gases because their particles move randomly from place to place.
Diffusion is an important process for living things; it is how substances move in and out of cells.
In gases and liquids, particles move randomly from place to place.
Diffusion is important because in living things, substances move in and out of cells by diffusion. For example:
Respiration produces waste carbon dioxide, causing the amount of carbon dioxide to increase in the cell. Eventually, the carbon dioxide concentration in the cell is higher than that in the surrounding blood. The carbon dioxide then diffuses out through the cell membrane and into the blood.
Water diffuses into plants through their root hair cells. The water moves from an area of high concentration (in the soil) to an area of lower concentration (in the root hair cell). This is because root hair cells are partially permeable. The diffusion of water like this, is called osmosis.