Explain how the structure of a villus epithelial cell (enterocyte) is adapted for the absorption of digested nutrients from the small intestine.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The apical surface of an enterocyte is covered with numerous microvilli, forming a brush border that increases surface area and provides more sites for transport proteins. Embedded in this membrane are carrier and channel proteins that mediate facilitated diffusion and active transport of digested nutrients such as glucose and amino acids. The cell contains many mitochondria that supply ATP for the active transport processes. The basolateral membrane lies close to the capillaries of the villus, allowing absorbed nutrients to enter the bloodstream (or lacteals for fats) rapidly.
Examiner tips
- Mention microvilli and surface area first; link to transport proteins; note ATP supply; explain proximity to capillaries
- Use terms ‘brush border’, ‘carrier proteins’, ‘active transport’, ‘basolateral membrane’
Common mistakes
- Confusing apical with basolateral membrane; not mentioning mitochondria; using vague terms like ‘lots of transporters’ instead of specific types
Mark scheme (4 marks)
- Microvilli / brush border greatly increases the surface area of the apical membrane
- Large numbers of mitochondria provide ATP for active transport of nutrients (e.g. glucose, amino acids) across the membrane
- Transport proteins (carrier proteins / channel proteins) embedded in the apical membrane allow facilitated diffusion or active transport of specific molecules
- The basal membrane / basolateral membrane is in close proximity to blood capillaries, allowing rapid transfer of absorbed nutrients into the blood / lymph (lacteals for fats)
Key terms in this question
enterocyte
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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