Biology · D Continuity and change. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Water is a polar solvent. Its molecules surround ions and polar molecules and hold them in solution. This is called solvation.
Osmosis is the net movement of water through a partially permeable membrane. Water moves from the solution with the lower solute concentration (hypotonic) to the solution with the higher solute concentration (hypertonic). Between isotonic solutions water still crosses in both directions, but at equal rates, so there is no net movement.
The effect depends on the cell. An animal cell has no wall, so it bursts in a hypotonic solution and shrinks in a hypertonic one. A plant cell has a wall, so it becomes turgid or plasmolysed instead.
Students divide by the final value when they calculate percentage change. Always divide the change by the initial value, and keep the minus sign for a loss.
Answer: About 0.35 mol dm−3. At this concentration there is no net movement of water.
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