4.4 Active transport

Question 1

What is active transport

Answer 1

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins

Question 2

What is ATP used for in active transport

Answer 2

1. Directly move molecules
2. Individually move molecules using a concentration gradient which has already been setup by direct active transport. This is co-transport

Question 3

How does active transport differ from passive forms of transport

Answer 3

1. Metabolic energy in the form of ATP is needed
2. Substances are moved against a concentration gradient, that is from a lower to a higher concentration
3. Carrier protein molecules which act as ‘pumps’ are involved
4. The process is very selective, with specific molecules being transported

Question 4

Describe the process of direct active transport of a single molecule

Answer 4

1. The carrier proteins span the plasma membrane and bind to the molecule or ion to be transported on one side of it
2. The molecule or ion binds to receptor sites on the carrier protein
3. On the inside of the cell, ATP binds to the protein causing it to split into ADP and a phosphate molecule. As a result, the protein molecule changes shape and opens to the opposite side of the membrane
4. The molecule or ion is then released to the other side of the membrane
5. The phosphate molecule is released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated. The phosphate molecule then recombines with ADP to form ATP during respiration