3.3.3 Digestion and absorption

Question 1

What is the function of amylase in digestion?

Answer 1

Amylase catalyses the conversion of starch into the smaller sugar maltose.

Question 2

Describe the role of bile salts in lipid digestion.

Answer 2

Bile salts emulsify lipids (they cause the lipids to form small droplets).

Question 3

Some people suffer from lactose intolerance. This can be caused by an inability to break down lactose in the upper small intestine.
Suggest which disaccharidase enzyme is deficient or missing in people who are lactose-intolerant.
[1 mark]

Answer 3

Lactase

Question 4

Some people suffer from lactose intolerance. This can be caused by an inability to break down lactose in the upper small intestine.
How are the digestion products of lactose absorbed across the epithelial cells of the ileum?
[2 marks]

Answer 4

• The digestion products of lactose/glucose and galactose are absorbed across the epithelial cells of the ileum by active transport with sodium ions…
• …via a co-transporter protein.

Question 5

What two major types of enzymes break down proteins?

Answer 5

Endopeptidases and Exopeptidases

Question 6

What are the functions of endopeptidases in digestion?

Answer 6

Endopeptidases act to hydrolyse peptide bonds within a protein.

Question 7

What are the functions of exopeptidases in digestion?

Answer 7

• Exopeptidases act to hydrolyse peptide bonds at the ends of protein molecules.
• They remove single amino acids from proteins.

Question 8

Where are products of digestion absorbed?

Answer 8

The products of digestion are absorbed across the ileum epithelium into the bloodstream.

Question 9

How are the digestion products of lipids absorbed across the epithelial cells of the ileum?

Answer 9

• Micelles help to move monoglycerides and fatty acids towards the epithelium where they get absorbed.
• Monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane.

Question 10

How are the digestion products of proteins absorbed across the epithelial cells of the ileum?

Answer 10

• Sodium ions are actively transported out of the epithelial cells into the ileum itself.
• They then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membranes, carrying the amino acids with them.

Question 11

Why are large molecules broken down into smaller molecules during digestion?

Answer 11

Large molecules must be broken down into smaller, soluble molecules so they can be absorbed into the bloodstream.

Question 12

What type of reaction breaks down food during digestion?

Answer 12

Hydrolysis reactions break bonds.

Question 13

State the name of the process by which fatty acids and glycerol enter the intestinal epithelial cell.
[1 mark]

Answer 13

Diffusion

Question 14

Explain the advantages of lipid droplet and micelle formation.
[3 marks]

Answer 14

• 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 15

Suggest how the Golgi apparatus is involved in the absorption of lipids.
[3 marks]

Answer 15

• Modifies/processes triglycerides;
• Combines triglycerides with proteins;
• Packaged for release/exocytosis;
  OR
• Forms vesicles;

Question 16

List three organelles that you would expect to be numerous and/or well developed in an epithelial cell of the ileum, giving a reason for your choice in each case.

Answer 16

• Endoplasmic reticulum to re-synthesise triglycerides from monoglycerides and fatty acids.
• Golgi apparatus to form chylomicrons from triglycerides, cholesterol and lipoproteins.
• Mitochondria to provide ATP required for the co-transport of glucose and amino acid molecules.

Question 17

Name the other chemical that moves across epithelial cells with glucose molecules during co-transport.

Answer 17

Sodium ions

Question 18

In addition to having microvilli, state one other feature of the epithelial cells of the ileum that would increase the rate of absorption of amino acids.

Answer 18

An increase in the number/density of protein channels and carrier proteins.