What distinguishes diffusion from facilitated diffusion?

Diffusion and facilitated diffusion are both types of passive transport mechanisms that allow substances to move across cell membranes, but they differ primarily in their reliance on transport proteins.

Facilitated diffusion is characterized by the use of specific transport proteins that assist in moving molecules across the membrane. This is particularly important for substances that cannot easily pass through the lipid bilayer of the cell membrane, such as glucose or ions. These proteins create pathways or channels through which these molecules can move down their concentration gradient without expending energy.

In contrast, simple diffusion involves the movement of molecules directly through the membrane without the help of transport proteins. This typically applies to small, nonpolar molecules like oxygen or carbon dioxide that can easily traverse the lipid bilayer.

Thus, the distinction lies in the fact that facilitated diffusion employs transport proteins, while diffusion does not. Both processes are passive, meaning they do not require cellular energy (ATP) to occur. The understanding of how facilitated diffusion operates as a transport mechanism is crucial for comprehending cellular functions, especially in contexts such as nutrient uptake and ion regulation.