One of the most important roles of cell membranes is to control what substances enter and leave the cell. Describe the difference and a briefly outline the mechanism for passive and active transport of molecules over cell membranes.

Passive transport requires no energy and is dependent on concentration difference gradient of intra and extracellular spaces. Channel protein can be opened or closed to allow or stop the free flow of molecules such as glucose to flow from an area of high concentration to an area of low. an example of this is Na+ ions in the Neuron. The action potential opens the voltage sensitive ion channel and Na+ ions flow from [high] extracellularly in to the cell.Active transport is ATP dependant. Energy must be released from the hydrolysis of ATP to ADP + Pi in order to move molecules against their concentration gradient. for example the NaKATPase transporter found in almost all cell types.