Answer:
Energy (in the form of ATP)
Explanation:
The main difference between active transport and passive transport is that active transport needs the energy to work. Active transport also moves molecules against the concentration gradient, kinda like a pump. This pump will need energy in the form of adenosine triphosphate (ATP) to keep it working. Adenosine triphosphate will be broken down into adenosine diphosphate (ADP). The energy from the breakdown reaction will be used by the pump.
