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

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

## Mark scheme (4 marks)

1. Lysosomes are surrounded by a single phospholipid bilayer membrane, which isolates hydrolytic enzymes from the rest of the cytoplasm / prevents self-digestion of the cell.
2. Lysosomes contain hydrolytic (digestive) enzymes / hydrolases, which catalyse the breakdown of macromolecules such as proteins, lipids, carbohydrates and nucleic acids.
3. The interior of the lysosome is maintained at an acidic pH (approximately pH 4.5–5), which is the optimum pH for lysosomal hydrolases to function / proton pumps in the membrane actively transport H⁺ ions into the lysosome to maintain this low pH.
4. Lysosomes can fuse with vesicles containing engulfed material (phagosomes / endosomes) or with damaged organelles, delivering enzymes directly to the substrate for digestion / allowing recycling of cellular components.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-9eb7fe83) · Published by Druglandscape Ltd.