Describe how the small intestine is adapted to absorb the products of digestion efficiently.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The small intestine has a very large surface area, achieved by the presence of villi – finger‑like projections on the inner wall. Each villus contains a dense network of capillaries and a lacteal, providing a rich blood supply. This extensive vascularisation maintains a concentration gradient, so that absorbed molecules such as glucose and amino acids diffuse continuously into the blood.
Examiner tips
- Use the exact terms: villi, capillaries, lacteal, concentration gradient, diffusion.
- Show the chain: large surface area → villi → capillaries → gradient → diffusion.
- Keep answer concise – one sentence per point to hit all four marks.
Common mistakes
- Confusing villi with microvilli or omitting the lacteal.
- Using vague phrases like ‘lots of blood’ instead of ‘dense network of capillaries’.
- Failing to mention the concentration gradient or diffusion as the driving force.
Mark scheme (4 marks)
- The small intestine has a large surface area
- Due to the presence of villi (finger-like projections / folds on the inner wall)
- Villi have a good blood supply / network of capillaries / are well supplied with blood vessels
- This maintains a concentration gradient so that absorbed molecules (e.g. glucose / amino acids) move continuously into the blood by diffusion
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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