Explain osmosis and explain why this is an important concept in maintaining water potential in animal cells.

Osmosis is a passive process by which water achieves equilibrium through a semi-permeable membrane, moving down a concentration gradient. Water will move from where it is in high concentration (ie in a low solute concentration or hypotonic) to where it is in low concentration (ie in a high solute concentration or hypertonic). When the concentration of water is equal on both sides of the membrane the water potential is reached and the net flow of water from one side to another ceases. The important principle of osmosis can be related to animal cells. The phospholipid bilayer acts as a semi-permeable membrane in this example. Placing red blood cells into hypertonic solution would cause the intracellular water to move out of the cell by osmosis, resulting in the cells shrivel up and look spiky in appearance. Conversely, placing RBCs into an hypotonic solution would cause water to move into the cells by osmosis and the cells would swell up, becoming turgid, and eventually burst. Maintaining the equilibrium is important as otherwise every time an animal had a drink of water, they risk their cells becoming turgid and so maintaining the correct amount of solutes prevents this.