Osmosis is the diffusion of water across a selectively permeable membrane. Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides.
H2O balance of Cells
• Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane.
• Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water.
• Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water.
• Hypertonic or hypotonic environments create osmotic problems for organisms.