Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Semi-permeable membranes allow certain molecules or ions to pass through by diffusion and occasionally specialized processes. They are crucial in maintaining cellular homeostasis and controlling the movement of substances in and out of cells.
Semi-permeable membranes are vital for osmoregulation, helping organisms maintain fluid balance.
These membranes often permit water molecules to pass freely while restricting larger solutes or ions.
In kidney function, semi-permeable membranes play a key role in filtering blood and forming urine.
Osmosis occurs across semi-permeable membranes, driving water movement based on solute concentration gradients.
Many biological membranes, such as the plasma membrane, are semi-permeable and contain protein channels for selective permeability.
Related terms
Osmosis: The process by which water molecules move across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
The passive movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached.
Plasma Membrane: The biological membrane that separates the interior of all cells from the outside environment, controlling substance passage due to its semi-permeability.