== Energy  == 

 I have edited the introduction, because previously it said that passive transport does not use any kind of energy. This is not true. Passive transport relies on the kinetic energy of the substance that is being transported. This kinetic energy is what causes it to move around and (by random chance) cross the membrane. The difference is that active transport actually uses the cell's energy (ATP or electrochemical gradient) to pump the substance across the membrane.