In what type of transport does a molecule move against its gradient using energy?

Active transport is the process in which molecules move against their concentration gradient, which means they are moving from an area of lower concentration to an area of higher concentration. This movement requires energy, typically derived from ATP, because it is against the natural tendency of molecules to spread out evenly.

In contrast, diffusion happens spontaneously and moves molecules down their concentration gradient without the need for energy input. Facilitated diffusion also allows substances to cross membranes with the help of transport proteins, but it still occurs down their concentration gradient, thus not requiring energy. Secondary active transport does involve the use of energy, but it relies on the gradient established by primary active transport to move other substances against their gradient.

Active transport is crucial for many cellular processes, such as maintaining proper ion concentrations and nutrient uptake, demonstrating the importance of energy in moving substances where they are needed most within the cell.