IGCSE Coordinated Science Vocabulary Practice Test

Osmosis is the movement of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential. Water potential drops when solutes are added or pressure increases, so water moves toward the more concentrated solution in an attempt to balance concentrations. The membrane lets water through but blocks most solutes, so the movement is driven by this gradient and does not require energy. This is why plant cells in pure water become turgid while cells in a salty solution lose water and shrink. The process is passive, unlike active transport, and it specifically involves water, not solutes.