Diffusion, osmosis and active transport are all transport processes. Diffusion refers to the movement of any molecules/ions apart from water whereas osmosis refers to the transport of only water. Active transport refers to the movement of dissolved solutes.Both diffusion and osmosis are passive processes that require no energy. On the other hand, active transport is an active process which requires ATP. Diffusion and osmosis move their respective substances down their concentration gradients (i.e. from high to low) whereas active transport moves substances from an area of low concentration to an area of high concentration.Diffusion and osmosis do not require carrier proteins whereas active transport does.