Describe the roles of bile in the chemical digestion of fats in the duodenum.

Cambridge International IGCSE Biology (0610) — 7.4 Chemical digestion · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Bile neutralises the acidic chyme from the stomach, providing a suitable pH for pancreatic lipase to act in the duodenum.
Bile also emulsifies large fat globules into smaller droplets, increasing their surface area.
The larger surface area allows lipase to access more triglyceride molecules, speeding up digestion.

Examiner tips

Use the word ‘neutralises’ and ‘emulsifies’ – examiners look for these terms. Show the link between pH, lipase activity and increased surface area. Keep each point short and to the point to fit the 4‑mark limit.

Common mistakes

Confusing bile with pancreatic enzymes. Forgetting to mention the pH effect or the surface‑area increase. Using vague phrases like ‘helps digestion’ without specifying how.

Mark scheme (4 marks)

Bile neutralises the acidic contents entering the duodenum from the stomach
This provides a suitable / optimum pH for lipase to work in the small intestine
Bile emulsifies fats / oils into smaller droplets
Emulsification increases the surface area of fats for lipase to act upon, speeding up digestion

Key terms in this question

bile · duodenum