Describe the process of active transport [4]

Active transport is when a protein moves a certain material across the membrane from a region of lower concentration to a region of higher concentration. This means the substance is absorbed against the concentration gradient and energy is needed for this active transport to work. The energy is usually comes from adenosine triphosphate or ATP, every cell supplies its own ATP by cell respiration. Globular proteins or pump proteins or transporter proteins in membranes carry out the active transport, the membrane must contain a lot of these proteins so that the cell can control the contents of its cytoplasm precisely. An example of active transport is in human nerve cells where potassium ions are pumped in and sodium ions are constantly transported out of the cell by active transport into the external fluid bathing the cell to build up a store of potential energy or an electrical impulse that is used to transmit a nerve impulse.