Mediated transport is the transport of molecules across the membrane with the help of a carrier. The molecule transported may be large and water soluble. The carriers have the capacity to bind either a single molecule or a group of similar molecules. This process is known as specificity. Similar molecules bind to the same carrier. Transport systems are of two kinds, namely active transport and passive transport. Passive transport does not require energy, whereas active transport requires energy. An example is the movement of Na⁺, K⁺-ATPase pump, which move in opposite directions across the membrane.