Define active transport.
The movement of molecules or ions into or out a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
How is ATP used in active transport?
- Directly move molecules.
- Individually move molecules using a concentration gradient that has been set up by direct active transport.(co-transport).
How is it different from passive forms of transport?
- Metabolic energy in the form of ATP is needed.
- Substances are moved against a concentration gradient, from low to high.
- Carrier proteins acting as ‘pumps’ are involved.
- The process is very selective so only specific substances are transported.
How does direct active transport of a single molecule or ion work?
- The carrier protein spans across the plasma membrane and it binds with the molecule or ion that is needed to be transported across.
- The molecule or ion binds to the receptor sites of the carrier protein.
- On the inside of the cell/organelle, ATP will bind with the protein, causing it to split into ADP and a phosphate molecule. This causes the protein to change shape and opens on the other side of the membrane.
- The molecule or ion is released onto the other side.
- The phosphate molecule is released from the protein and this causes the protein to change back into its original shape, ready for the process to be repeated. The phosphate molecule them recombines with the ADP to form ATP during respiration.
What’s the similarities and differences between active transport and facilitated diffusion?
- Both use carrier proteins.
- But facilitated diffusion occurs down the concentration gradient whereas active transport goes against a concentration gradient.
- Facilitated diffusion does not require metabolic energy but active transport does, in forms of ATP.
Can more than one molecule or ion be moved in the same direction at the same time by active transport?
Yes and occasionally, the molecule or ion that moves in is the same molecule or ion that moves out. e.g. sodium-potassium pump.
Briefly explain what happens at the sodium-potassium pump?
- Sodium ions are actively removed from the cell.
- Potassium ions are actively taken in from the surrounding.
