Osmosis (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• All cells are surrounded by a cell membrane which is partially permeable
• Water can move in and out of cells by osmosis
• Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane
• In doing this, water is moving down its concentration gradient
• The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)

Osmosis and the partially permeable membrane