AP BIOLOGY

Detailed explanation-1: -During active transport, substances move against the concentration gradient, from an area of low concentration to an area of high concentration. This process is “active” because it requires the use of energy (usually in the form of ATP). It is the opposite of passive transport.

Detailed explanation-2: -Diffusion. During diffusion, substances move from an area of high concentration to an area of low concentration, until the concentration becomes equal throughout a space. Image showing the process of diffusion across the plasma membrane. Initially, the concentration of molecules is higher on the outside.

Detailed explanation-3: -To move substances against a concentration or electrochemical gradient, a cell must use energy. Active transport mechanisms do just this, expending energy (often in the form of ATP) to maintain the right concentrations of ions and molecules in living cells.