Active Transport
The scientific definition of active transport is the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy. In active transport, the cell expends energy in the form of ATP to move a substance against its concentration gradient. It’s a lot more work than passive transport, and the proteins in the bilayer do most of the work during active transport. They pull the substances, usually ions, from areas of lower concentration into areas of higher concentration. This is one of the three membrane proteins used to do active transport, called a carrier protein. An example would be, like a very crowded amusement park, pushing through a lot of people to get from one place to another. Some transporters bind to ATP directly and use the energy of its hydrolysis to drive active transport. Other transporters use the energy already stored in the gradient of a directly –pumped ion. Direct active transport of the ion establishes a concentration gradient. When this is relieved by facilitated diffusion, the energy released can be harnessed to the pumping of some other ion, or molecule.