Which type of cellular transport occurs against the concentration gradient?

Active transport is the type of cellular transport that occurs against the concentration gradient, meaning 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 molecules inside and outside of cells, which is critical for various cellular functions.

Active transport requires energy, typically in the form of ATP, because it is working against the natural tendency of molecules to diffuse from areas of high concentration to areas of low concentration. This is different from passive transport methods such as facilitated diffusion and osmosis, which occur without the input of metabolic energy and move substances along their concentration gradients, thereby maintaining equilibrium.