Topic 2---B: Cell Membranes- 4. Active Transport

Question 1

What is active transport ?

Answer 1

• Its the transport of molecules or ions across a cell membrane from a low to high concentration (against a concentration gradient).
• Carrier proteins and co-transporters are involved.
• Active process

Question 2

Differences between active transport and faciliated diffusion?

Answer 2

• Active transport usually moves solutes from a low to high concentration but in faciliated diffusion they always move from a high to a low concentration.
• Active transport requires energy (active process) but faciliated diffusion does not (passive process).
• Active transport doesn’t use channel proteins.

Question 3

Carrier proteins

Answer 3

• The process is pretty similar to faciliated diffusion.
• Molecule attatches to a carrier protein.
• Protein changes shape.
• This moves the molecules across the membrane, releasing it on the other side.

Question 4

ATP (active transport)

Answer 4

• This is a (molecule produced by repiration)
• It’s a common source of energy in the cell so it’s important for active transport.
• ATP undergoes a hydrolysis reaction, splitting into ADP and pi (inorganic phosphate)
• This releases energy so that solutes can be transported.

Question 5

Co-transporters

Answer 5

• It’s a type of carrier protein.
• They bind two molecules at a time.
• The concentration gradient of one molecules is used to move the other molecule against it’s own concentration gradient.

Question 6

Stages of active transport

Answer 6

• Molecules or ions bind with specific carrier proteins.
• ATP binds to the carrier protein and splits into ADP and phosphate releasing energy.
• This causes the carrier protein to change shape and allow the molecule or ion to cross the membrane.
• Phosphate is released from the protein causing it to revert to it’s original shape.

Question 7

What is co-transport?

Answer 7

• It uses a concentration gradient set up by active transport of another molecule or ion.

Question 8

Co- transport stages

Answer 8

1. Sodium ions are actively transported out of the epithelial cells in the ilieum into the blood by the sodium-potassium pump.
   This creates a concentration gradient- there is now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.
2. This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell down their concentration gradient. They do this via the sodium-glucose co-transporter proteins.
   - The co-transporter carries glucose into the cell with sodium so the concentration of glucose in the cell increases.
3. Glucose diffuses out of the cell into the blood down it’s concentration gradient through a protein channel by faciliated diffusion.

Question 9

Factors affecting the rate of active transport?

Answer 9

• The number of carrier proteins present- the more proteins there are the faster the rate of active transport.
• The speed of individual carrier proteins- the faster they work the faster the rate of active transport.
• The rate of respiration in the cell and the availability of ATP