Facilitated diffusion differs from ordinary diffusion primarily in the way molecules move across cell membranes. While both processes transport substances down their concentration gradients, facilitated diffusion requires specific transport proteins to assist in the movement of certain molecules.
In facilitated diffusion:
- A concentration gradient is maintained: Unlike ordinary diffusion, which can eventually equalize concentrations across a membrane, facilitated diffusion does not fully eliminate the concentration gradient. Molecules still move from areas of higher concentration to lower concentration but often remain in unequal concentrations.
- Transport proteins are involved: Facilitated diffusion utilizes membrane proteins to help larger or polar molecules that can’t easily pass through the lipid bilayer of the cell membrane. These proteins can be channel proteins or carrier proteins that only allow specific substances to pass through.
- It occurs at a regulated rate: The rate of facilitated diffusion can be limited by the number of available transport proteins. Once all the proteins are occupied, increasing the concentration gradient will not enhance the rate of diffusion.
Overall, facilitated diffusion is a specialized process that allows cells to efficiently transport necessary molecules while still maintaining a concentration gradient, unlike ordinary diffusion, which tends toward equilibrium.