What type of transport involves moving substances against their concentration gradient?

Active transport is the process that involves moving substances against their concentration gradient, meaning that molecules are moved from an area of lower concentration to an area of higher concentration. This type of transport requires energy, typically in the form of ATP, because it is working against the natural flow of diffusion, which tends to move substances from areas of higher concentration to areas of lower concentration.

In contrast, facilitated diffusion, passive transport, and simple diffusion all rely on the natural tendency of particles to move from higher to lower concentrations without the input of additional energy. These processes help to maintain equilibrium in a cell but do not involve the movement against a concentration gradient. Active transport is essential for various cellular functions, such as nutrient uptake and waste removal.