Biology – 3.2 Osmosis | e-Consult

Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of high water concentration to a region of low water concentration. Water moves down its water potential gradient. This movement occurs through the cell membrane, which is a selectively permeable barrier. Water can move across the membrane freely, but the movement of larger molecules is restricted. Therefore, water moves into a cell if the surrounding solution has a lower concentration of solutes (and thus a higher water potential) than the cell's cytoplasm. Conversely, water moves out of a cell if the surrounding solution has a higher concentration of solutes (and thus a lower water potential) than the cell's cytoplasm.