Explain how the structure of a neutrophil is related to its function in the immune response.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Neutrophils are the most abundant white blood cells in human blood and are typically the first immune cells to arrive at a site of infection.
Model answer (4 marks)
1. The multi‑lobed nucleus gives the neutrophil a flexible shape, enabling it to squeeze through the narrow gaps between endothelial cells (diapedesis) and reach sites of infection.
2. Numerous lysosomes (granules) contain hydrolytic enzymes that destroy engulfed pathogens after phagocytosis.
3. The flexible plasma membrane forms pseudopodia, allowing the neutrophil to engulf bacteria into a phagosome.
4. A high number of mitochondria supplies ATP for the energy‑intensive processes of chemotaxis and phagocytosis.
2. Numerous lysosomes (granules) contain hydrolytic enzymes that destroy engulfed pathogens after phagocytosis.
3. The flexible plasma membrane forms pseudopodia, allowing the neutrophil to engulf bacteria into a phagosome.
4. A high number of mitochondria supplies ATP for the energy‑intensive processes of chemotaxis and phagocytosis.
Examiner tips
- Use the exact terms: multi‑lobed nucleus, diapedesis, lysosomes, pseudopodia, ATP, mitochondria.
- Show the link between structure and function for each point.
- Keep each point concise and separate with numbers or bullet points.
- Avoid unnecessary explanation of unrelated processes.
Common mistakes
- Confusing neutrophils with other white blood cells (e.g., lymphocytes).
- Omitting the role of the nucleus in diapedesis.
- Failing to mention the energy requirement or mitochondria.
Mark scheme (4 marks)
- Neutrophils have a multi-lobed (polymorphic) nucleus, allowing the cell to squeeze through narrow gaps between capillary endothelial cells (diapedesis) to reach infected tissue.
- Neutrophils contain numerous lysosomes (granules) packed with hydrolytic / digestive enzymes, enabling them to destroy pathogens after phagocytosis.
- Neutrophils carry out phagocytosis: the flexible cell surface membrane allows pseudopodia to form, engulfing pathogens into a phagosome.
- Neutrophils have many mitochondria to supply ATP required for the energy-demanding processes of movement (chemotaxis) and phagocytosis.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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