Explain why the large surface area of the ileum wall is important for the absorption of the products of digestion.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The ileum is the main site of absorption in the alimentary canal. Its inner wall has many finger-like projections called villi, and each epithelial cell on the surface of a villus has further protrusions called microvilli.
Model answer (4 marks)
A larger surface area allows more molecules to cross the intestinal wall simultaneously, increasing the rate of absorption.
This means digested food can be absorbed more quickly and efficiently.
Consequently sufficient glucose, amino acids, fatty acids and glycerol enter the bloodstream to meet the body's needs.
The nutrients can then be assimilated into cells and used for energy, growth and repair.
This means digested food can be absorbed more quickly and efficiently.
Consequently sufficient glucose, amino acids, fatty acids and glycerol enter the bloodstream to meet the body's needs.
The nutrients can then be assimilated into cells and used for energy, growth and repair.
Examiner tips
- Use the exact wording from the mark scheme, e.g. "larger surface area", "rate of absorption", "sufficient nutrients".
- Show the logical link: surface area → more molecules cross → faster absorption → enough nutrients for metabolism.
- Keep each point brief and to the point – 4 marks, one sentence each.
Common mistakes
- Writing a long paragraph that repeats the same idea instead of separate points.
- Using vague terms like "more nutrients" without specifying the types or the effect on the body.
Mark scheme (4 marks)
- A larger surface area means more molecules can pass through the wall of the intestine at the same time / per unit time.
- This increases the rate of absorption / allows digested food to be absorbed more quickly / efficiently.
- So that sufficient / enough nutrients (glucose, amino acids, fatty acids and glycerol) move into the bloodstream to meet the body's needs.
- So that nutrients can be assimilated into cells and used in metabolic reactions / for energy / growth and repair.
Key terms in this question
absorption · surface area · ileum
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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