Moving against a concentration gradient
Active transport: the movement of molecules or ions across a cell membrane from a lower concentration to a higher concentration using carrier proteins and energy from ATP hydrolysis.
Active transport allows cells to transfer substances against their concentration gradients. The net direction is therefore opposite to diffusion, where particles move overall from higher to lower concentration.
Carrier proteins perform the transport. Different carriers are specific to particular molecules or ions.
Uses of active transport
- Kidney tubule cells recover useful filtered solutes and return them to the blood.
- Cells of the digestive tract take up certain molecules produced by digestion.
- Sugars made in leaves can be transferred into phloem for transport elsewhere in the plant.
- Root hair cells can build up mineral ions absorbed from the soil.
Concentration
A substance can be transferred from where its concentration is lower to where it is higher.
ATP
ATP is hydrolysed to ADP and inorganic phosphate. The released energy enables the carrier protein to adopt a different conformation.