Explain how the villi of the small intestine are adapted to absorb glucose efficiently into the blood, referring to both diffusion and active transport in your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
1. Glucose diffuses from the intestinal lumen into the epithelial cells of the villi down a concentration gradient.
2. Inside the epithelial cells, glucose is transported into the blood by active transport.
3. This active transport uses carrier proteins and requires ATP produced by cellular respiration.
4. The villi have a large surface area, which increases the rate of diffusion.
5. The villi contain a rich capillary network that keeps the blood glucose concentration low, maintaining the gradient for active transport.
2. Inside the epithelial cells, glucose is transported into the blood by active transport.
3. This active transport uses carrier proteins and requires ATP produced by cellular respiration.
4. The villi have a large surface area, which increases the rate of diffusion.
5. The villi contain a rich capillary network that keeps the blood glucose concentration low, maintaining the gradient for active transport.
Examiner tips
- Use the exact terms ‘diffusion’ and ‘active transport’. Mention carrier proteins and ATP. Show the villi’s large surface area and rich capillary supply. Keep each point brief and separate with numbers.
Common mistakes
- Confusing diffusion for active transport. Forgetting to mention ATP or carrier proteins. Over‑describing villi structure instead of linking it to absorption.
Mark scheme (5 marks)
- Glucose moves by diffusion from the small intestine lumen into the epithelial cells / villus cells down a concentration gradient
- Active transport is used to move glucose from the epithelial cells into the blood / capillaries when the concentration of glucose in the blood is higher than in the cells
- Active transport requires energy (from respiration) / uses carrier proteins
- Villi have a large surface area to increase the rate of absorption / diffusion
- Villi have a rich blood supply / capillary network that maintains a concentration gradient for glucose
Key terms in this question
diffusion · active transport · villi
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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