Explain how glucose moves from a high concentration in the small intestine into an epithelial cell, and then how it moves from a low concentration inside the epithelial cell into the bloodstream against a concentration gradient.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Glucose is absorbed in the small intestine. The concentration of glucose inside the epithelial cells lining the small intestine is lower than in the intestinal lumen, but higher than in the blood capillaries nearby.
Model answer (5 marks)
Glucose moves from the small intestine into the epithelial cell by diffusion, because it moves from a high concentration in the lumen to a lower concentration in the cell, i.e. down a concentration gradient.
Glucose then moves from the epithelial cell into the bloodstream against a concentration gradient by active transport. Active transport requires energy, which is supplied by ATP produced in respiration, and uses carrier proteins in the cell membrane to move glucose into the blood.
Glucose then moves from the epithelial cell into the bloodstream against a concentration gradient by active transport. Active transport requires energy, which is supplied by ATP produced in respiration, and uses carrier proteins in the cell membrane to move glucose into the blood.
Examiner tips
- Use the word ‘diffusion’ for the first part and ‘active transport’ for the second. Mention the concentration gradient and the need for ATP. Include carrier proteins as the mechanism. Keep the answer concise and to the point.
Common mistakes
- Confusing diffusion with active transport for the first step. Forgetting to state that active transport requires ATP. Omitting the role of carrier proteins in active transport.
Mark scheme (5 marks)
- Glucose moves from the small intestine into the epithelial cell by diffusion
- Diffusion occurs because glucose moves from a high concentration (in the lumen) to a low concentration (in the epithelial cell) / down a concentration gradient
- Glucose moves from the epithelial cell into the blood against a concentration gradient by active transport
- Active transport requires energy (from respiration / ATP)
- Active transport uses carrier proteins (in the cell membrane) to move glucose
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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