Osmosis (Tonicity) | Cell Biology

Osmosis is defined as the net movement of water molecules across a semi-permeable membrane from an area of low solute concentration to high solute concentration. This occurs when solutes are too large to pass through the membrane, necessitating water movement through the membrane or aquaporins.

The concept of tonicity is explained by comparing solute concentrations. A hypotonic solution has low solute concentration and high water potential, while a hypertonic solution is more concentrated with low water potential. Water naturally flows toward the hypertonic side to reach equilibrium.

Using red blood cells as an example, the video illustrates how cells behave in different environments. In isotonic solutions, they stay balanced; in hypertonic solutions, cells shrink as water exits; and in hypotonic solutions, cells swell and risk bursting as water enters.