What type of transport involves particles moving from an area of lower concentration to an area of higher concentration?

Active transport is a process in which particles move against their concentration gradient, meaning they travel from an area of lower concentration to an area of higher concentration. This movement requires energy, usually in the form of ATP, because it is working against the natural tendency for molecules to diffuse from areas of high concentration to low concentration.

In contrast, passive transport, facilitated diffusion, and simple diffusion all allow substances to move from areas of higher concentration to areas of lower concentration without the use of energy. Therefore, active transport is the correct answer for scenarios involving movement against the concentration gradient.