Osmosis (Cambridge (CIE) O Level Biology): Revision Note

Osmosis

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

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

• Osmosis is the net movement of water molecules from a high water potential (dilute solution) to a low water potential (more concentrated solution) 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)

Partially permeable membrane diagram

Osmosis and the partially permeable membrane, where water molecules move through a partially permeable membrane from a region of high water potential to a region of low water potential