Diffusion is the process by which molecules move from areas of high concentration, to areas of low concentration. When the molecules are even throughout a space – it is referred to as equilibrium state.
Concentration gradient: This is the difference between concentrations in a given environment.
Molecules will always travel down the concentration gradient, toward areas of smaller concentration. Example: food coloring that disperses out in a glass of water the dispersal of the fume from an air freshener sprayed in a room.
Semi Permeable membranes: These are membranes that allow the passage of some things while at the same time disallowing the passage of other things through it. Example of a semi-permeable membrane is the cell wall. It allows water and oxygen to pass freely through the cell’s membrane, by diffusion
Osmosis means the diffusion of water across a membrane. Water will normally travel in the direction where there is a high concentration of solute. In other words where there is a lower concentration of water.
Salt is a solute and when it is concentrated inside or outside the cell, it will pull the water up to its direction. This is also the reason why we are thirsty after eating salty food.