How is passive transport different then active transport?

An example of passive transport would be the process of osmosis (water diffusing between a membrane-- from an area of high concentration to an area of low concentration). It is known as passive transport because no energy is needed in order to move the water across the membrane. When no energy is needed to move the substance it is considered passive transport. On the other hand, when energy IS needed to transport molecules or substances across a membrane it is referred to as active transport. An example of this would be a calcium pump located in the lipid bilayer of a plasma membrane which can transport potassium (K+) ions across it. Energy is needed in order to move those potassium ions across the membrane, and therefore is referred to as active transport.