Cells: Transport Across Membranes - Active Transport

Question 1

What is active transport?

Answer 1

• Active transport uses energy to move molecules and ions across plasma membranes against a concentration gradient
• Or from an area of lower concentration to an area of higher concentration

Question 2

What types of molecules are involved in active transport?

Answer 2

• Carrier proteins
• Co-transporters
• ATP

Question 3

What do carrier proteins do?

Answer 3

• A molecule attaches to a carrier protein
• The protein changes shape
• This moves the molecule across the membrane, releasing it on the other side

Question 4

How is ATP involved in active transport in carrier proteins?

Answer 4

• ATP will bind to the protein and will be hydrolysed into ADP and Pi
• This releases energy so the solutes can be transported against their concentration gradient

Question 5

What are co-transporters?

Answer 5

• Co-transporters are a type of carrier protein
• They bind two molecules at a time
• The concentration gradient of one molecule is used to move the other molecule against its own concentration gradient
• Uses one molecule moving down its concentration gradient to move another molecule against its own concentration gradient

Question 6

Describe the co-transport of glucose and sodium ions in the ileum

Answer 6

• Sodium ions are actively transported out of the epithelial cell into the blood
• This reduces the sodium ion concentration in the epithelial cell
• Sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell
• The sodium ions diffuse through a co-transported protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient
• Glucose then moves by faciliated diffusion from epithelial cell to the blood

Question 7

Factors Affecting the Rate of Active Transport

Answer 7

• Speed of individual carrier proteins
- The faster they work, the faster the rate of active transport

• The number of carrier proteins present
- The more proteins there are, the faster the rate of active transport

• The rate of respiration in the cell and the availability of ATP
- If respiration is slow, ATP will be produced slower, so active transport will occur slower