In osmosis, when the two sides are balanced, the pressure is called what?

• A. Isotonic Pressure
• B. Hypertonic Pressure
• C. Hypotonic Pressure
• D. Osmotic Pressure

Answer: (A)

Isotonic pressure describes a balance where the solute concentrations on both sides are equal, so there is no net movement of water across the membrane. In osmosis, water moves from the side with lower solute concentration to the side with higher concentration. When the concentrations are balanced (isotonic), these driving forces cancel, and the system is in equilibrium. That state is represented by isotonic pressure. Hypertonic and hypotonic describe unbalanced conditions where water would move out or in, respectively, while osmotic pressure is the force that drives water movement across a membrane; the balanced state is best described as isotonic pressure.