What are the differences between diffusion, osmosis and active transport?

Diffusion is the net movement of particles in solution across a partially permeable membrane. The net movement of particles is from higher to lower concentration gradient.

Osmosis is the net movement of water molecules across a water permeable membrane from areas of low solute concentration to high solute concentration.

Active transport occurs when cells need to move substances across membranes against the concentration gradient. This requires energy, in the form of ATP.