Which statement is true about active transport?

Active transport is a process that requires energy to move substances across a cell membrane against their concentration gradient. This means that molecules are transported from an area of lower concentration to an area of higher concentration, which is the opposite direction of what would occur naturally via passive transport mechanisms like diffusion. The energy used in active transport typically comes from ATP (adenosine triphosphate), which is the primary energy currency of the cell.

The requirement of energy is a defining characteristic of active transport, as opposed to passive transport methods, which do not require energy and occur solely based on the concentration gradient. Such energy-dependent mechanisms are crucial for maintaining cellular homeostasis and allowing cells to uptake necessary nutrients and expel waste products, even when those substances are in lower concentrations outside the cell.