Final answer:
Active transport is the method used to move molecules against the concentration gradient, requiring energy from ATP.
Step-by-step explanation:
When molecules must be moved against the concentration gradient, that is from an area of low concentration to an area of high concentration, the method of transport required is active transport. Unlike passive or facilitated diffusion, which occur down a concentration gradient and do not require energy, active transport requires energy to move molecules. The energy for this process is typically provided by ATP (adenosine triphosphate), which is produced by the cell through cellular respiration. In active transport, specific proteins in the cell membrane function as pumps to move substances across the membrane against their concentration gradient, allowing the cell to maintain essential functions like nutrient uptake and waste removal.