What kind of transport requires energy to move substances across a cell membrane?

Active transport is the process that requires energy to move substances across a cell membrane. This is because it involves the movement of molecules against their concentration gradient, meaning that substances are moved from an area of lower concentration to an area of higher concentration. This process is essential for maintaining the proper concentrations of ions and other molecules within the cell, which is crucial for various cellular functions.

Energy is typically supplied in the form of ATP (adenosine triphosphate) during active transport. The cell effectively uses this energy to power transport proteins, such as pumps, which help in the movement of substances.

In contrast, processes like passive transport, facilitated diffusion, and osmosis do not require energy as they move substances along their concentration gradient—from areas of higher concentration to areas of lower concentration—thereby utilizing the natural kinetic energy of the molecules. This distinction is key to understanding how different transport mechanisms operate within biological systems.