DigestionAQA A-Level Biology: Subtopic test

1. 1
   A person eats a meal of bread, which is rich in starch. The starch is digested during passage through the gut and the products are absorbed across the epithelium of the small intestine.

   (a)

   Which enzyme hydrolyses starch to maltose?

   [1 mark]

   • AMaltase
   • BLipase
   • CAmylase
   • DEndopeptidase

   (b)

   Where is the enzyme maltase found?

   [1 mark]

   • ADissolved in saliva
   • BIn the cell surface membrane of the epithelial cells lining the small intestine
   • CDissolved in pancreatic juice
   • DDissolved in bile

   (c)

   Explain why the maltose formed from starch must be hydrolysed further before it can be absorbed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A person eats a meal containing a large amount of fat. The fat is digested in the small intestine by lipase from the pancreas, with the help of bile, which is made in the liver, stored in the gall bladder and released into the small intestine.

   (a)

   Which are the products of the hydrolysis of triglycerides by lipase?

   [1 mark]

   • AGlycerol and amino acids
   • BGlucose and fatty acids
   • CMaltose and glycerol
   • DMonoglycerides and fatty acids

   (b)

   What is the role of bile salts in lipid digestion?

   [1 mark]

   • AThey emulsify lipids into smaller droplets
   • BThey hydrolyse the ester bonds in triglycerides
   • CThey change the tertiary structure of lipase so it works faster
   • DThey hydrolyse peptide bonds in lipoproteins

   (c)

   Explain how bile salts increase the rate of digestion of the fat.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Proteins in food are digested in the stomach and the small intestine by a series of enzymes. A dietary protein contains a single polypeptide chain of 90 amino acids.

   (a)

   Describe the roles of endopeptidases, exopeptidases and membrane-bound dipeptidases in the digestion of the protein.

   [3 marks]

   (b)

   An endopeptidase hydrolyses the polypeptide at five different peptide bonds. Calculate the number of shorter polypeptides produced and explain how this increases the rate at which exopeptidases release amino acids.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital studies digestion in the small intestine. One patient has chronic pancreatitis, in which the pancreas secretes much less pancreatic juice. In the laboratory, a student also investigates how bile salts affect the rate at which lipase digests the fat in milk.

   (a)

   Pancreatic juice contains amylase, lipase and peptidases. The patient with chronic pancreatitis has pale, fatty stools and has lost weight. Explain the effects of the reduced pancreatic secretion on the digestion of carbohydrates, lipids and proteins.

   [6 marks]

   (b)

   In the investigation, the pH of a mixture of milk and lipase fell from 8.0 to 6.0 in 4 minutes with bile salts, and from 8.0 to 7.5 in 4 minutes without bile salts. Calculate the rate of change of pH in each mixture and explain the difference.

   [6 marks]

   Total for question 4: 12 marks

End of questions