What is the term for the energy-requiring process that moves substances against their concentration gradient?

The term for the energy-requiring process that moves substances against their concentration gradient is active transport. This process involves the use of ATP or another energy source to transport molecules from an area of lower concentration to an area of higher concentration, essentially working against the natural tendency of molecules to move towards equilibrium. Active transport is crucial for maintaining the proper concentrations of ions and other substances within cells, which is vital for various cellular functions, including nerve impulse transmission and muscle contraction.

Facilitated diffusion, in contrast, is a passive process that relies on specific transport proteins to help molecules move down their concentration gradient, meaning no energy is used. Osmosis is specifically the movement of water across a selectively permeable membrane and also occurs down its concentration gradient. Endocytosis involves the cell membrane engulfing substances to bring them into the cell, but this process is more about the bulk transport of larger molecules or particles rather than directly moving substances against their concentration gradient. Thus, active transport stands out as the correct term for the energy-dependent movement against concentration gradients.