Exam qs

• Describe how a molecule of starch is digested into glucose (5 marks)

  • Salivary amylase hydrolyses starch into maltose
  • Pancreas makes pancreatic amylase which further hydrolyses starch into maltose
  • Membrane-bound maltase hydrolyses maltose into glucose
  • Glycosidic bonds are broken
• Explain the advantage of lipid droplet and micelle formation (3)

  • Droplets increase surface area
  • So faster hydrolysis of lipids
  • Micelles carry fatty acids and glycerol to epithelial cell membrane
• The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how (2)

  • exopeptidases hydrolyse peptide bonds at the ends of a protein and endopeptidases hydrolyse internal peptide bonds within a polypeptide.
  • this creates more ‘ends’
• How are Golgi apparatus involved in absorption of lipids?

  • modifies triglycerides
  • combines triglycerides with proteins
  • packages for exocytosis
• Explain how digestion of starch in the gut leads to an increase in the concentration of glucose in the blood. (3)

  • hydrolysed by amylase
  • produces glucose
  • small enough to diffuse across the gut wall into the blood
• Describe the complete digestion of starch by a mammal (4)

  • hydrolysis
  • of glycosidic bonds
  • starch is hydrolysed into maltose by amylase
  • maltose is hydrolysed into glucose by maltase (membrane-bound)
• Describe the processes involved in the absorption and transport of digested food molecules from the ileum into lymph vessels (5)

  • micelles contain bile salts and monoglycerides
  • releases monoglycerides to lining of ileum
  • monoglycerides absorbed by diffusion
  • triglycerides reformed in cells
  • vesicles move to cell membrane
• Describe the role of micelles in the absorption of fats into the cells lining the ileum (3)

  • micelles include bile salts and fatty acids
  • make fatty acids more soluble in water
  • release fatty acids to lining of the ileum
  • maintain high concentration of fatty acids to lining of the ileum
  • fatty acids absorbed by diffusion