Describe the roles of the stomach and the pancreas in the digestion of proteins.

Pearson Edexcel International GCSE Biology (4BI1) — 2.6 Nutrition: humans · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The stomach secretes the protease pepsin, which hydrolyses protein chains into smaller peptides and amino acids. Pepsin works best in the acidic environment of the stomach, where the low pH activates the enzyme. The pancreas also produces proteases (trypsin, chymotrypsin and carboxypeptidase) and releases them into the duodenum. In the small intestine these pancreatic enzymes further break down the peptides into free amino acids for absorption.

Examiner tips

  • Mention both pepsin and pancreatic proteases, and note the acidic pH for pepsin.
  • Show the sequence: stomach → pepsin → acidic environment → pancreas → duodenum.
  • Use the exact terms ‘protease’, ‘pepsin’, ‘pancreas’, ‘duodenum’ and ‘low pH’.
  • Keep the answer short – one sentence per point to fit 4 marks.

Common mistakes

  • Confusing pepsin with trypsin or vice‑versa.
  • Omitting the acidic environment as the reason for pepsin activity.
  • Writing that the pancreas releases enzymes into the stomach instead of the duodenum.

Mark scheme (4 marks)

  1. The stomach produces protease (pepsin / gastric protease).
  2. Protease breaks down proteins into amino acids.
  3. The pancreas also produces protease and releases / secretes it into the small intestine (duodenum).
  4. The stomach provides an acidic environment / low pH that is the optimum for protease activity in the stomach.

Key terms in this question

stomach · pancreas

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