Active transport is different from passive transport in that during active transport, molecules move against the concentration gradient, which means they move from a low-concentration area to a high-concentration area. On the other hand, passive transport moves with the concentration gradient.
Concentration gradient is the difference of concentration between an area of high concentration and an area of low concentration. This concentration gradient is found in body cells, and it is much higher on the inside of a cell than the outside.
However, when molecules are carried out of a cell, when it’s burned-out, it moves from a higher- to a lower-concentration gradient. This process uses passive transport.
Passive transport is unlike active transport in that the process does not need a source of chemical energy to move the carrier and its substances. However, active transport requires this chemcial energy, which often comes from Adenosine Triphosphate, or ATP, used in cells as a sort of currency for energy transfers. This energy is needed to carry molecules from a high-concentration gradient to a lower-concentration gradient.
Both active and passive transport play an important role in ensuring that molecules are carried to where they are needed within the body. This process occurs in all living organisms.