A solution with no net movement of water across the membrane is described as

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

Answer: (C)

Tonicity describes how a surrounding solution affects water movement by osmosis. When the outside solution has the same solute concentration as the inside, there’s no net movement of water across the membrane because the tendency for water to move in or out balances out. This is an isotonic situation, where cell volume stays the same. If the outside is more concentrated (hypertonic), water leaves the cell and it shrinks; if the outside is less concentrated (hypotonic), water enters and the cell swells. Osmotic pressure is the force created by differences in solute concentration that drives water movement, not the state of zero net movement itself.