How does osmosis move water across a semipermeable membrane?

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Artist's illustration of human nerve cells showing a central neuron with a green nucleus, branching dendrites, and glowing signals traveling along axons against a dark background. — cell Artist's conception of a human neuron.

In biology, osmosis is the spontaneous diffusion of water across a semipermeable membrane. This process occurs as water moves from an area of lower solute concentration to an area of higher solute concentration.12

Because the cell membrane consists of a lipid bilayer that is often impermeable to many solutes, water molecules frequently travel through specialized protein channels known as aquaporins. This movement is a form of passive transport, meaning it does not require the cell to expend energy. The process continues until the concentration of solutes is balanced or until the osmotic pressure—the pressure required to stop the flow—is sufficient to counteract the movement.2314