Direct active transport

• Carrier proteins span the plasma membrane, and have receptor sites that can bind to a specific molecule/ion on the outside of the cell.
• On the inside of a cell/organelle, ATP binds to the carrier protein, causing it to split into ADP and Pi. This causes the carrier protein to change shape and open to the other side of the membrane, whilst releasing the molecule/ion.
• The Pi is then released from the protein which causes the protein to revert to its original shape, so the process can be repeated. The Pi then recombines with the ADP to form ATP during respiration.