Digestion

Question 1

Describe what is meant by diffusion

Answer 1

Digestion is the process in which large insoluble molecules are hydrolysed into smaller soluble molecules which can be absorbed and used by the body.

Question 2

Why do molecules need to be small and soluble

Answer 2

• Small - diffuse across the phospholipid bilayer
• Soluble - dissolve in plasma/tissue fluid for transport

Question 3

Describe how proteins are digested in the human gut.

Answer 3

1. Hydrolysis of peptide bonds;
2. Endopeptidases break polypeptides into smaller peptide chains;
3. Exopeptidases remove terminal amino acids;
4. Dipeptidases hydrolyse / break down dipeptides into amino acids.

Question 4

Describe the role of the enzymes of the digestive system in the complete breakdown of starch.

Answer 4

Amylase
(Starch) to maltose
Maltase; Maltose to glucose; Hydrolysis;
(Of) glycosidic bond;

Question 5

Explain how digestion of starch in the gut (small intestine) leads to an increase in the concentration of glucose in the blood. Details of co-transport are not required.

Answer 5

1. Hydrolysed by enzymes
2. Produces glucose (in the gut);
3. Small enough to cross the gut wall (into the blood) / monomers / monosaccharides (can) cross the gut wall (into the blood);

Question 6

Coeliac disease is a disease of the human digestive system. In coeliac disease, the microvilli are damaged. Although people with coeliac disease can digest proteins they have low concentrations of amino acids in their blood. Explain why they have low concentrations of amino acids in their blood.

Answer 6

• Reduced surface area; (So) less absorption;
• (Membrane-bound) enzymes less effective; (So) proteins / polypeptides not digested;
• Cell membranes damaged; (So) Fewer / less effective carrier / channel proteins;
• Carrier / channel proteins damaged; (So) less absorption;

Question 7

Suggest and explain why the combined actions of
endopeptidases and exopeptidases are more efficient than exopeptidases on their own.

Answer 7

Endopeptidases hydrolyse the internal peptide bonds, whereas exopeptidases hydrolyse peptide bonds at the end. This increases the surface area by providing more ends for enzymes to act upon

Question 8

H. pylori is a type of bacteria that can cause stomach ulcers. A stomach ulcer is where proteases or stomach acid damages the stomach’s own lining.Suggest and explain which part of the stomach is likely damaged by H. pylori to allow this to happen

Answer 8

• H. pylori damages the epithelial cells
• Therefore less mucus is secreted. - - Therefore there is less protection against the acid, causing the lining to become damaged

Question 9

In biliary obstruction, the ducts that secrete bile into the small intestine are blocked. Explain why people with biliary obstruction cannot absorb their food very well

Answer 9

• Less bile enters the small intestine
• Therefore acid from the stomach is not neutralised
• Therefore, the enzymes secreted by the pancreas and brush border in the small intestines are denatured as the hydrogen bonding in their tertiary structure is overcome
• Therefore, the enzymes’ active sites are no longer complementary to the substrates
• As a result the polymers are not hydrolysed into monomers and so cannot be absorbed as they are too large