Active transport

Question 1

Define 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 + carrier proteins

Question 2

In active transport, what is ATP used to do?

Answer 2

• Directly move molecules
• Individually move molecules using a concentration grad. which has already been set up by (direct) active transport - this is known as co-transport

Question 3

How does active transport differ from passive forms of transport?

Answer 3

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

Question 4

Why will carrier proteins only transport particular substances across the membrane?

Answer 4

Carrier proteins have a specific tertiary structure. They have binding sites - these are different to the active site of enzymes.
(* Synoptic link - carrier proteins in active + co-transport linked to protein structure)

Question 5

Describe the active transport of a single molecule/ion

Answer 5

• Carrier proteins span the plasma membrane + bind to the molecule/ion to be transported on one side of it
• The molecule/ion binds to receptor sites on carrier protein
• On the inside of cell/organelle, ATP binds to protein, causing it to split into ADP + a phosphate molecule
• As a result, protein molecule changes shape + opens to the opposite side of the membrane
• Phosphate molecule is released from the protein which causes the protein to revert to its original shape, ready for process to be repeated
• Phosphate molecule then recombines with the ADP to form ATP during respiration

Question 6

What is the difference between facilitated diffusion + active transport?

Answer 6

Both use carrier proteins but:

• Facilitated diffusion occurs down a concentration gradient, while active transport occurs against a concentration gradient
• This means facil. diffusion does not require metabolic energy, while active transport does
• Metabolic energy is provided in the form of ATP

Question 7

Give an example of active transport where the molecule/ion is moved into a cell/organelle at the same time as a different one is being removed from it

Answer 7

Sodium-potassium pump:

• Na+ ions are actively removed from the cell/organelle while K+ ions are actively taken in from surroundings (K+ pumped in & Na+ pumped out)
• This creates concentration gradients across the membrane
• This process is essential to a no. of important processes in the organism, including the creation of a nerve impulse

Question 8

Describe how a sodium-potassium pump works

Answer 8

• Molecules bind to carrier protein + ATP attaches to the membrane protein on the inside of cell/organelle
• Binding of phosphate ion to protein causes the protein to change shape so that access for the molecules is open to the inside of the membrane but closed on the outside