3.3 - Digestion and absorption

Question 1

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5)

Answer 1

• Micelles contain bile salts and fatty acids/monoglycerides
• Make fatty acids/monoglycerides (more) soluble (in water)
  / Bring/release/carry fatty acids/ monoglycerides to cell/lining (of the iluem)
  / Maintain high(er) concentration of fatty acids/ monoglycerides to cell/lining (of the ileum)
• Fatty acids/monoglycerides absorbed by diffusion
• Triglycerides (re)formed (in cells)
  ‘accept chylomicrons form’
• Vesicles move to cell membrane

Question 2

Describe the role of micelles in the absorption of fats into the cells lining the ileum. (3)

Answer 2

• Micelles include bile salts and fatty acids
• Make the fatty acids (more) soluble in water
• Bring/release/carry fatty acids to cell/lining (of the ileum)
• Maintain high(er) concentration of fatty acids to cell/lining (of the ileum)
• Fatty acids (absorbed) by diffusion
  ‘accept fats/lipids for fatty acids’

Question 3

Describe the role of enzymes in the digestion of proteins in a mammal. (4)

Answer 3

• (Reference to) hydrolysis of peptide bonds
• Endopeptidase act in the middle of protein/polypeptide
  /Endopeptidase produces short(er) polypeptides/ increase number of ends
• Exopeptidases act at end of protein/polypeptide
  / Exopeptidase produces dipeptides/amino acids
• Dipeptidase acts on dipeptide/between two amino acids
  /Dipeptidase produces (single) amino acids

Question 4

Explain the advantages of lipid droplet and micelle formation. (3)

Answer 4

• Droplets increase surface areas (for lipase / enzyme action)
• (So) faster hydrolysis / digestion (of triglycerides / lipids)
• Micelles carry fatty acids and glycerol /monoglycerides to/through membrane to (intestinal epithelial) cell

Question 5

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. (3)

Answer 5

• Sodium ions actively transported from ileum cell to blood
• Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose)
• Glucose enters by facilitated diffusion with sodium ions