Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration aided by a concentration gradient.
Diffusion continues to occur as long as there is a difference in concentration between two regions (concentration gradient). Some processes that depend on diffusion include the following:
1. Gaseous exchange: Movement of gases through respiratory surfaces is by diffusion.
2. Absorption of materials into cells Cells obtain raw materials and nutrients from the surrounding tissue fluid and blood through diffusion, e.g, glucose needed for respiration diffuses from blood and tissue fluid into cells.
3. Excretion: Removal of metabolic waste products like carbon (IV) oxide, and ammonia out of cells is by diffusion.
4. Absorption of the end-products of digestion from the intestines is by diffusion.