Explain how the ultrastructure of a pancreatic acinar cell is adapted for the secretion of digestive enzymes.

IB DP Biology Higher Level (2023 syllabus) — B2.3 Cell specialisation · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Abundant rough endoplasmic reticulum (RER) provides the site for synthesis and translation of digestive enzymes, which are secretory proteins.
A prominent Golgi apparatus modifies, packages and directs the enzymes into secretory vesicles.
Zymogen (secretory) granules accumulate at the apical surface, storing inactive enzyme precursors ready for exocytosis.
Numerous mitochondria supply ATP to power the energy‑demanding processes of synthesis, vesicle transport and exocytosis.

Examiner tips

  • Use the word ‘adapted’ to link structure to function. Mention the apical surface to show localisation. Show the flow: RER → Golgi → granules → exocytosis. Include mitochondria as an energy source.

Common mistakes

  • Confusing RER with smooth ER. Forgetting to mention the apical localisation of granules. Omitting the role of mitochondria or the energy requirement of exocytosis.

Mark scheme (4 marks)

  1. Abundant rough endoplasmic reticulum (RER) provides the site for synthesis/translation of digestive enzymes (secretory proteins).
  2. A prominent Golgi apparatus modifies, packages, and directs the enzymes into vesicles for secretion.
  3. Zymogen (secretory) granules accumulate at the apical surface, storing inactive enzyme precursors ready for exocytosis.
  4. Numerous mitochondria supply ATP to power the energy-demanding processes of synthesis, vesicle transport, and exocytosis.

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