Which type of transport requires a membrane protein?

The type of transport that requires a membrane protein is facilitated diffusion. This process involves the movement of molecules across a cell membrane down their concentration gradient, but unlike simple diffusion, facilitated diffusion cannot occur directly through the lipid bilayer. Instead, it relies on specific transport proteins embedded in the membrane. These proteins act as channels or carriers that help polar or charged substances that cannot easily cross the hydrophobic lipid bilayer move into or out of the cell.

Facilitated diffusion is crucial for the transport of ions, glucose, and other essential molecules, allowing cells to maintain homeostasis and regulate their internal environments effectively. This transport method is energy-efficient since it does not require ATP; the molecules will move along their concentration gradient.

Other transport mechanisms, such as simple diffusion, filtration, and osmosis, do not necessarily involve membrane proteins. Simple diffusion allows small nonpolar molecules (like oxygen) to pass directly through the membrane. Filtration is driven by pressure differences and does not rely on protein assistance. Osmosis, while it does involve water movement, can occur through both protein channels (aquaporins) and directly through the bilayer, but it does not require proteins in all cases. Thus, facilitated diffusion is distinct in its dependence on membrane proteins for