Active transport can be defined as the movement of molecules or ions into and out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrierproteins.
In active transport, ATP is used to directly move molecules. It is also used to individually move molecules using a concentration gradient set up by direct active transport (co-transport).
Active transport differs from passive transport in that it requires metabolic ATP energy.
Active transport involves the movement of molecules or ions against the concentrationgradient, whilst passive transportation involves the movement of molecules or ions down the concentrationgradient.
Active transport requires carrier protein molecules which act as 'pumps', whilst passive modes of transport don't.
Active transport is a highly selective process in terms of only specific substances being transported.
Both active transport and facilitated diffusion use carrier proteins, however active transport occurs against the concentration gradient and requires ATP energy, whilst facilitated diffusion occurs down the concentration gradient and doesn't require ATP energy.
In the sodium-potassium pump, sodium ions are actively removed from the cell, whilst potassium ions are actively taken in from the surroundings.
