Co-Transport

Question 1

Where does the absorption of the products of digestion occur in

Answer 1

The ileum of the small intestine

Question 2

Where are the microvilli found

Answer 2

The epithelial cells lining the small ileum

Question 3

What adaptations for transport does the small intestine have

Answer 3

• Microvilli provide a large surface area for the insertion of carrier proteins through which diffusion, facilitated diffusion and active transport can take place
• Capillaries contain flowing blood which maintains the concentration gradient
• Walls of the villi are one cell thick so there is a shorter diffusion pathway

Question 4

What is the significance of the epithelial cells containing lots of mitochondria

Answer 4

Mitochondria synthesises ATP, so they are well adapted for active transport, since it requires a lot of ATP

Question 5

Describe how glucose and amino acids can diffuse into the blood

Answer 5

- Carbohydrates and proteins are continually broken down into glucose and amino acids within the ileum
- This means there is a high concentration gradient of glucose and amino acids in the ileum
- Therefore, glucose and amino acids can diffuse into the blood

Question 6

What is the limitation of relying on diffusion alone to transport the products of digestion?

Answer 6

Equilibrium

Question 7

Define Co-Transport

Answer 7

Absorption occur against a concentration gradient

Question 8

Describe the process of Co-Transport

Answer 8

• Sodium ions are actively transported out of epithelia cells by the sodium-potassium pump into the blood.
• This maintains a higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells.
• Sodium ions move via facilitated diffusion int
  the epithelial cells through a co-transport protein. As sodium ions diffuse through, the carrier changes shape allowing amino acids or glucose into the cell.
• Glucose or amino acids then move from the epithelial cell into the capillary by facilitated diffusion

Question 9

Explain how the structure of the epithelial cells is adapted for their function

Answer 9

• Many mitochondria to produce lots of ATP for active transport
• Microvilli to increase surface area increasing
  rate of exchange
• Numerous transport proteins across the
  membrane to increase rate of exchange