Explain why glucose moves out of the small intestine into the blood after a meal.

WJEC GCSE Biology (Wales) — 1.1.2 Movement of substances · Explain · 4 marks · View as Markdown

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

After a meal, the digestion of carbohydrates produces large amounts of glucose in the small intestine. This glucose needs to reach the body's cells via the bloodstream.

Model answer (4 marks)

Glucose moves out of the small intestine into the blood by diffusion.
The concentration of glucose in the intestinal lumen is higher than in the bloodstream after a meal.
Substances therefore move from the area of higher concentration (intestine) to the area of lower concentration (blood).
Blood flow keeps the concentration gradient, so diffusion continues and glucose enters the circulation.

Examiner tips

  • Use the word ‘diffusion’ and explain the concentration gradient. Mention the role of blood flow to maintain the gradient. Keep the answer short and to the point, matching the four mark points.

Common mistakes

  • Confusing diffusion with active transport. Forgetting to mention the higher concentration in the intestine. Not stating that blood flow maintains the gradient.

Mark scheme (4 marks)

  1. Glucose moves by diffusion
  2. There is a higher concentration of glucose in the small intestine than in the blood
  3. Substances move from an area of higher concentration to an area of lower concentration
  4. Blood flow maintains / keeps the concentration gradient (so diffusion continues)

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