Osmosis (Cambridge (CIE) IGCSE Biology): Revision Note

Osmosis

• All cells are surrounded by a cell membrane which is partially permeable

• Water can move in and out of cells across the cell membrane by osmosis

• Osmosis is the diffusion of water molecules from a dilute solution (low solute concentration) to a more concentrated solution (high solute concentration) across a partially permeable membrane

  • The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)

• In doing this, water is moving down the concentration gradient from where there is more water to where there is less