Active transport

Sometimes substances need to be moved from where there is there is a low concentration to where there is a high concentration - against the concentration gradient. This allows the cell to take up essential molecules even when they are at low concentration outside.

Because molecules are being moved against the concentration gradient, it requires energy. It is thought that active transport uses the same protein carriers as those involved in facilitated diffusion. The energy used is ATP. Cells which carry out active transport have more mitochondria to produce the ATP needed through respiration.