Explain how the structural features of the peroxisome are suited to its function in the detoxification of hydrogen peroxide and the oxidation of fatty acids.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Peroxisomes are bounded by a single membrane that keeps the toxic contents, such as hydrogen peroxide, inside the organelle and prevents it from damaging the cytosol.
The membrane contains catalase, an enzyme that rapidly decomposes hydrogen peroxide into water and oxygen, thereby detoxifying the cell.
Inside the peroxisome are oxidase enzymes that carry out beta‑oxidation of fatty acids. This reaction breaks fatty acids into acetyl‑CoA and produces hydrogen peroxide as a by‑product.
Thus, the single‑membrane compartmentalisation isolates the reactive oxygen species and other toxic intermediates from sensitive cellular components (e.g. DNA, other organelles), protecting cellular integrity.
The membrane contains catalase, an enzyme that rapidly decomposes hydrogen peroxide into water and oxygen, thereby detoxifying the cell.
Inside the peroxisome are oxidase enzymes that carry out beta‑oxidation of fatty acids. This reaction breaks fatty acids into acetyl‑CoA and produces hydrogen peroxide as a by‑product.
Thus, the single‑membrane compartmentalisation isolates the reactive oxygen species and other toxic intermediates from sensitive cellular components (e.g. DNA, other organelles), protecting cellular integrity.
Examiner tips
- Mention the single membrane and its role in containing toxic contents; cite catalase and oxidase enzymes; link beta‑oxidation to H₂O₂ production; explain isolation of ROS protects DNA and organelles.
Common mistakes
- Failing to state that the peroxisome has only one membrane; not naming catalase or oxidase; confusing peroxisomes with mitochondria; omitting the protective aspect of compartmentalisation.
Mark scheme (4 marks)
- Peroxisomes are bounded by a single membrane that contains the toxic contents / prevents hydrogen peroxide from leaking into the cytosol.
- Peroxisomes contain catalase, which breaks down hydrogen peroxide to water and oxygen, detoxifying the cell.
- Peroxisomes contain oxidase enzymes that carry out beta-oxidation of fatty acids, breaking them down into acetyl-CoA / generating hydrogen peroxide as a by-product of this process.
- Compartmentalisation within the peroxisome ensures that reactive oxygen species / toxic intermediates are isolated from sensitive cell components such as DNA or other organelles, protecting cellular integrity.
Key terms in this question
peroxisome · hydrogen peroxide
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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