The transport of molecules across the plasma membrane of a living cell by a process that involves a specific transmembrane carrier (see transport protein) located within the plasma membrane but does not require expenditure of energy by the cell. The carrier combines with a molecule at one face of the membrane, then changes shape so the molecule is moved through the membrane and released at the opposite face. It enables the diffusion through the membrane of molecules that otherwise could not pass through. For example, fructose is transported from the intestinal lumen into epithelial cells by the GLUT5 transporter in the apical membrane. Compare active transport.