Active transport differs from diffusion in that it requires energy to complete its task. It is powered by the splitting of ATP or by concentration gradients maintained by various pumps (e.g., the sodium-potassium pump). Active transport processes don't need a natural gradient, and can transport materials against gradients.
There are two types of active transport:
- Primary - directly uses energy to transport molecules across a membrane (1)
- Secondary - there is no direct coupling of ATP
- instead, the electrochemical potential difference created by pumping ions out of cells is used. The two main forms of this are counter- and co-transport. (1)