Explain how glucose is absorbed from the small intestine into the blood when the concentration of glucose in the blood is already higher than in the small intestine.

AQA GCSE Biology (8461) — 4.1.3 Transport in cells · Explain · 4 marks · View as Markdown

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

After digestion, glucose must move from the small intestine into the bloodstream. Sometimes the concentration of glucose inside the intestine is lower than in the blood.

Model answer (4 marks)

Glucose cannot move by simple diffusion because it would have to move against the concentration gradient.

Instead, glucose is taken up by active transport.

Active transport moves glucose from the dilute intestinal lumen into the more concentrated blood, against the gradient.

This process requires energy, which is supplied by ATP produced in cellular respiration.

Examiner tips

  • Use the word ‘active transport’ and explain it moves against the gradient.
  • Mention that glucose cannot diffuse when the blood concentration is higher.
  • State that the energy comes from ATP/respiration.
  • Keep the answer concise and use the exact terminology.

Mark scheme (4 marks)

  1. Glucose cannot move by diffusion (because it would need to move against the concentration gradient)
  2. Active transport is used to move glucose from the small intestine into the blood
  3. Active transport moves substances from a more dilute to a more concentrated solution (against the concentration gradient)
  4. Active transport requires energy from respiration

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