# Explain how the structure of the lysosome is related to its function in intracellular digestion.

> IB DP Biology Higher Level (2023 syllabus) — B2.2 Organelles and compartmentalisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Lysosomes are bounded by a single phospholipid bilayer membrane that isolates hydrolytic enzymes from the rest of the cytoplasm, preventing self-digestion of the cell.
2. The interior (lumen) of the lysosome is maintained at an acidic pH (approximately 4.5–5), which is the optimum pH for the hydrolytic enzymes contained within.
3. Lysosomes contain acid hydrolases (e.g. proteases, lipases, nucleases, glycosidases) that can break down all major classes of biological macromolecules.
4. Lysosomes fuse with phagosomes (containing engulfed material) or autophagosomes (containing worn-out organelles), delivering enzymes directly to their substrates to enable digestion and recycling of components.

## Key terms

- [lysosome](https://www.gradenine.co.uk/glossary/lysosome)
- [intracellular digestion](https://www.gradenine.co.uk/glossary/intracellular-digestion)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-8a95cb44) · Published by Druglandscape Ltd.