Describe the structural features of villi that make them well adapted for the absorption of digested food in the ileum.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Villi are finger‑shaped projections of the mucosa that
1. increase the surface area of the ileum, allowing more food to be absorbed;
2. have a single‑cell thick epithelium, giving a short diffusion distance for glucose and amino acids;
3. contain a network of blood capillaries that carry absorbed nutrients into the bloodstream;
4. contain a lacteal, a lymph vessel that absorbs fatty acids, glycerol and other lipids.
1. increase the surface area of the ileum, allowing more food to be absorbed;
2. have a single‑cell thick epithelium, giving a short diffusion distance for glucose and amino acids;
3. contain a network of blood capillaries that carry absorbed nutrients into the bloodstream;
4. contain a lacteal, a lymph vessel that absorbs fatty acids, glycerol and other lipids.
Examiner tips
- Use the word "villi" and list the four features; keep each point short and clear.
- Show the link between structure and function (surface area, thin wall, capillaries, lacteal).
Common mistakes
- Confusing villi with microvilli or omitting the lacteal; writing the villi as two‑cell thick instead of single‑cell; not mentioning the blood capillaries.
Mark scheme (4 marks)
- Villi increase the surface area (of the small intestine / ileum) for absorption
- Villi have a thin (single-celled / one-cell thick) wall / epithelium, so substances have a short diffusion distance
- Villi contain a network of blood capillaries (to carry away absorbed glucose and amino acids)
- Villi contain a lacteal (lymph vessel) to absorb fatty acids and glycerol / lipids
Key terms in this question
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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