Which process is an example of facilitated diffusion?

Facilitated diffusion is a passive transport process that allows substances to cross membranes with the assistance of special proteins, without the expenditure of energy. Glucose transport using GLUT (Glucose Transporters) is a prime example of this process. In facilitated diffusion, molecules such as glucose are too large or polar to pass through the lipid bilayer of the cell membrane freely. The GLUT proteins span the membrane and provide specific binding sites for glucose, which causes conformational changes in the transporter protein that allow glucose to move into the cell along its concentration gradient.

This mechanism is crucial for cells, especially in tissues like muscle and fat, that require glucose for energy. By employing specific transporter proteins, the cell can regulate glucose uptake according to its needs without using ATP, exemplifying the nature of facilitated diffusion.