What process involves the use of membrane proteins to help move substances along a concentration gradient?

Facilitated diffusion is the correct process that involves the use of membrane proteins to help move substances along a concentration gradient. In facilitated diffusion, specific proteins embedded in the cell membrane act as channels or carriers, allowing certain molecules, such as glucose or ions, to cross the membrane more easily than they would on their own. This process is essential for transporting substances that are too large or polar to pass through the lipid bilayer directly.

The characteristic that distinguishes facilitated diffusion from other forms of transport is its reliance on membrane proteins while still moving substances down their concentration gradient, meaning it does not require an input of energy. This ensures that as molecules move from areas of higher concentration to lower concentration, they are guided by these proteins, ensuring efficient transport across membranes.

In contrast, processes like passive transport include a broader category that encompasses both facilitated diffusion and simple diffusion, while active transport refers to the movement of substances against their concentration gradient, which requires energy. Simple diffusion involves the direct movement of small or nonpolar molecules across the lipid bilayer without the assistance of proteins. Therefore, understanding facilitated diffusion is critical as it highlights the specific role of membrane proteins in aiding the transport of substances in line with their concentration gradients without expending energy.