Explain how the ultrastructure of a goblet cell in the intestinal epithelium is adapted for the secretion of mucus.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Goblet cells are unicellular glands interspersed among the columnar epithelial cells lining the small intestine. They continuously synthesise and secrete mucus glycoproteins (mucins) onto the epithelial surface.
Model answer (4 marks)
Goblet cells have an extensive rough endoplasmic reticulum, providing a large membrane surface for ribosome‑bound synthesis of mucin glycoproteins.
They contain a prominent Golgi apparatus that glycosylates and packages the mucins into secretory vesicles.
Numerous large mucus granules are present in the apical cytoplasm, ready for rapid exocytosis onto the epithelial surface.
A high number of mitochondria supply the ATP required for synthesis, modification and the exocytotic process.
They contain a prominent Golgi apparatus that glycosylates and packages the mucins into secretory vesicles.
Numerous large mucus granules are present in the apical cytoplasm, ready for rapid exocytosis onto the epithelial surface.
A high number of mitochondria supply the ATP required for synthesis, modification and the exocytotic process.
Examiner tips
- Use the word "abundant" or "extensive" for rER, "prominent" for Golgi, "numerous" for mucus granules, and mention "mitochondria" for ATP supply.
- Show the link between structure and function – e.g. rER for synthesis, Golgi for processing, granules for storage, mitochondria for energy.
- Keep the answer concise, 4 points, no extra wording.
Common mistakes
- Confusing smooth ER with rough ER; forgetting to mention ribosomes.
- Omitting the Golgi apparatus or describing it as small.
- Failing to mention mitochondria or the energy requirement.
Mark scheme (4 marks)
- Abundant rough endoplasmic reticulum (rER) provides an extensive membrane system for the synthesis of mucin glycoproteins by membrane-bound ribosomes.
- A large, well-developed Golgi apparatus processes and glycosylates the mucin proteins, packaging them into secretory vesicles for export.
- Numerous large mucus (secretory) granules / vesicles in the apical cytoplasm store mucin ready for rapid exocytosis onto the epithelial surface.
- Many mitochondria supply the ATP needed to drive active synthesis, protein modification, and the exocytotic secretion of mucus.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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