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facilitated diffusion
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Diagram of a cell membrane showing three types of membrane transport: simple diffusion of small molecules, facilitated diffusion through transporter proteins, and primary active transport using ATP to move molecules across the membrane. Labels identify the hydrophilic heads and hydrophobic tails of phospholipids, as well as extracellular and intracellular surfaces.
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facilitated diffusion

biochemistry
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Diagram of a cell membrane showing three types of membrane transport: simple diffusion of small molecules, facilitated diffusion through transporter proteins, and primary active transport using ATP to move molecules across the membrane. Labels identify the hydrophilic heads and hydrophobic tails of phospholipids, as well as extracellular and intracellular surfaces.
different types of membrane transport The cell membrane contains proteins that transport ions and water-soluble molecules into or out of the cell. Some molecules are able to freely diffuse across the membrane in a process known as simple diffusion.

Facilitated diffusion is a type of passive transport that allows molecules to move across a cell membrane down their concentration gradient, from an area of high concentration to an area of low concentration. This process does not require energy input from the cell.12

Instead of passing directly through the lipid bilayer, molecules that cannot easily penetrate the membrane, such as sugars and amino acids, utilize specific membrane transport proteins. These proteins act as "facilitators," binding to the molecule on one side of the membrane and undergoing a conformational change to release it on the other side. This mechanism is crucial for transporting vital substances like glucose and bicarbonate ions across the cell membrane.12

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2 Britannica Sources
  1. cell - The glucose transporter
  2. cell - The anion transporter

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