Active transport uses energy, Passive transport does not.
(I couldn't figure out how to respond to the answer above, which said the answer was Osmosis. I don't think this is true as osmosis involves water, and is much more specific. Passive transport is the correct answer, at least on Edge.)
Passive transport does not require energy for movement in and out of a place or across a membrane e.g a cell.
Osmosis uses passive transport to move materials in and out of a cell by setting up concentration gradient through a distance.
Osmosis can be defined as the movement of molecules or particles of a solution from an area of higher concentration to that of lower concentration through a semi-permeable membrane e.g plasma membrane. As we can see, the difference in concentration is the drive for the transport between the two medium. When the concentration is the same, there won't be any movement again.
