|Process||Descriptions||Substances moved||Energy required|
|Diffusion||Substances move from a high to a low concentration down a concentration gradient||Carbon dioxide, oxygen, water, food substances, wastes, eg urea||No|
|Osmosis||Water moves from a high to a low concentration across a partially permeable membrane and down a concentration gradient||Water||No|
|Active transport||Substances move against a concentration gradient||Mineral ions into plant roots, glucose from the gut into intestinal cells, from where it moves into the blood||Yes|
A gradient is a slope. The diagram below shows the direction of movement of particles by diffusion, osmosis and active transport on a concentration gradient.