What characterizes active transport?

Active transport is characterized by the requirement of energy to move molecules against their concentration gradient. This means that substances are transported from an area of lower concentration to an area of higher concentration, which is the opposite direction of what would occur naturally through diffusion. This process is essential for maintaining crucial concentration differences of ions and molecules across cell membranes, which can be critical for various cellular functions.

The energy used in active transport often comes from ATP (adenosine triphosphate), allowing cells to take in nutrients or expel waste products in scenarios where simple diffusion would not suffice. This mechanism is vital for processes such as nutrient absorption in intestinal cells, elimination of waste, and the maintenance of ion gradients in nerve and muscle cells, which are crucial for functions such as signal transmission and muscle contraction.