Describe the roles of the stomach in the digestion of food.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The stomach carries out physical digestion by churning and muscular contractions, which mix the food with gastric juice and increase its surface area for enzyme action. Gastric juice contains the protease enzyme pepsin, which chemically digests proteins into peptides and amino acids. Hydrochloric acid in the juice provides an acidic pH (≈2) that optimises pepsin activity and also kills harmful microorganisms in the food.
Examiner tips
- Use the term ‘churning’ or ‘muscular contractions’ for mechanical digestion.
- Mention both pepsin and hydrochloric acid and their dual roles (enzyme activity and defence).
- Show the link between increased surface area and enzyme efficiency.
- Keep the answer concise – 4 points only.
Common mistakes
- Confusing pepsin with other proteases or omitting the acidic pH requirement.
- Failing to state that the stomach’s mechanical action increases surface area for chemical digestion.
- Using vague terms like ‘mixing’ without specifying churning or muscular contractions.
Mark scheme (4 marks)
- The stomach carries out physical (mechanical) digestion by churning / muscular contractions mixing the food
- Physical digestion increases the surface area of food for enzyme action / chemical digestion
- Gastric juice / protease enzymes are secreted in the stomach to chemically digest proteins (to amino acids)
- Hydrochloric acid in gastric juice provides an optimum (acidic) pH for protease / pepsin activity AND / OR kills harmful microorganisms in food
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →