Practice question

Osmosis defined as net movement of water across selectively permeable membrane driven by difference in water chemical potential. Water moves from region of higher free water concentration, meaning low solute, to lower free water where solute high, until equilibrium of potentials or balance by hydrostatic pressure. Membrane restricts solute passage due to size or polarity exclusion. Process requires no metabolic energy, purely passive diffusion using thermal kinetic energy. Aquaporins may accelerate but do not require ATP. Common misconception conflates solute diffusion with osmosis. Solutes also diffuse down own concentration gradients from high to low via simple lipid diffusion if hydrophobic or via carriers channels, but that transport is termed diffusion or facilitated diffusion, not osmosis. Water pathway involves hydrogen bonding network transient breaking. Saying solutes move from high to low as part of osmosis mislabels transport; during osmosis solutes largely remain on original side, otherwise gradient would dissipate without water shift. Correct distinction clarifies tonicity effects: water moves, solutes generally retained, establishing osmotic pressure.