What is diffusion and osmosis?
Diffusion takes place primary in liquids and gases, this is because liquids and gases are made up of tiny particles called molecules. The particles have energy which enables them to move about constantly in random directions. Because these particles move about in random directions, they spread out to occupy / fill any available spaces.
So Diffusion is the process by which molecules move from an area that they are in high concentration to an area that they are in low concentration, until all particles (molecules) are evenly distributed.
Diffusion in gases can be demonstrated using bromine.
Diffusion in liquids can be demonstrated using a crystal of potassium permanganate and water.
See video below for diffusion in liquids and gases.
What is osmosis?
Osmosis is basically a special kind of diffusion, which involves water molecules passing through a partially permeable membrane from a solution that they are in high concentration to one that they are in low concentration. Water will move by osmosis from the more diluted solution (hypotonic) to the more concentrated solution (hypertonic), if both solutions are separated by a partially permeable membrane. The aim of osmosis is to equalize the solution concentration on both sides of the partially permeable membrane.
N.B. Partially permeable membrane as tiny holes/openings, that are selective as it relates to which particles pass through it.
See video below for osmosis.