Diffusion

The natural phenomonom caused by the tendency of small particles to spread out evenly within any given space. 

Simple diffusion:

Type-passive 

Movement of particles through the phospolipid bilayer or through channels from an area of high concentrartion to an area of low concentration-that is, down the concentration gradiant. 

Ex.)Movement of carbon dioxide out of all cells ; movement of sodium ions into nerve cells as they conduct an impulse. 

Dialysis:

Type-passive

Diffusion of small solute particles, but not larger solute particles, through a selectively permeable membrane; results in seperation of large and small solutes. 

Ex)During procedure called peritoneal dialysis, small solutes diffuse from blood vessles but blood proteins do not (thus removing only small solutes from the blood)