Osmosis

Osmosis is the net movement of water across a selectively permeable membrane toward a region of higher solute concentration. It occurs because differences in water chemical potential drive water across the membrane.

Water potential: Water potential measures the potential energy of water relative to a reference state and predicts its direction of movement. Water moves during osmosis down a water-potential gradient, which solute concentration helps create.
Solute: A solute is a substance dissolved in a solvent to form a solution. Differences in dissolved solute help establish the water-potential gradient driving osmosis.
Osmoregulation: Osmoregulation is the control of water and dissolved-solute balance in an organism. Organisms regulate internal conditions to manage osmotic water movement across cell membranes.
Osmolarity: Osmolarity is the concentration of osmotically active particles per unit volume of solution. Osmolarity estimates particle concentration but does not by itself account for membrane permeability.
Semipermeable membrane: A semipermeable membrane allows some substances to pass while restricting others. Osmosis requires a barrier that passes water more readily than the relevant solute.
Solution: A solution is a homogeneous mixture in which one or more substances are dissolved in another. Osmosis compares water movement between solutions separated by a selective barrier.
Turgor pressure: Turgor pressure is the pressure of a plant cell’s contents against its cell wall. Osmotic water entry can build the pressure that supports nonwoody plant tissues.
Osmolality: Osmolality is the concentration of osmotically active particles per kilogram of solvent. It measures solute particle abundance on a solvent-mass basis, distinct from observed water flow.
Chemical potential: Chemical potential is the change in a system’s free energy when the amount of a substance changes. Water’s chemical-potential difference supplies the thermodynamic driving force for osmosis.
Diffusion: Diffusion is the net spread of particles from regions of higher concentration to lower concentration through random motion. Unlike general diffusion, osmosis specifically concerns water crossing a selectively permeable membrane.

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