- Active transport - the movement of moleules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier proteins
Active transport allows cells to exchange molecules against a concentration gradient, metabolic energy is required for this. Once inside the molecules are prevented from leaking back out by the barrier of the cell surface membrane's bi-layer. This means a different environment is maintained on either side of the membrane.
Active transport is different from passive forms of transport in the following ways:
- Metabolic energy in the form of ATP is needed
- Materials are moved against a concentration gradient, i.e. from lower to higher
- Carrier protein molecules which act as 'pumps' are involved
- The process is very selective, with specific substances being transpored. The carrier proteins accept the molecule to be moved and the molecule enters the cell as a result of a change in shape of the carrier protein
Active transport uses ATP in one of two ways:
- By using ATP directly to move molecules
- By using a concentration gradient that has already been set up by direct active transport. Also known as co-transport.
Direct active transport of a single molecule or ion:
- Carrier proteins span the cell-surface membrane and accept the molecules or ions to be transported on one side of it
- The molecules or ions bind to receptors on the channels of the carrier…