What type of transport requires energy in the form of ATP?

Active transport is a process that requires the utilization of energy in the form of ATP to move substances across a cell membrane against their concentration gradient. This means that substances are transported from an area of lower concentration to an area of higher concentration, which is not a spontaneous process and therefore requires energy input.

In contrast, facilitated diffusion, simple diffusion, and osmosis do not require energy because they rely on the natural movement of molecules from high to low concentration. In facilitated diffusion, carrier proteins assist the movement of substances across the membrane, while simple diffusion involves the direct passage of molecules through the lipid bilayer, and osmosis is specifically the diffusion of water through a semipermeable membrane. All of these processes are driven by concentration gradients and do not necessitate ATP. Thus, active transport is unique in its requirement for energy to transport substances against their natural flow.