# Explain how B lymphocytes and T lymphocytes differ in their roles during the adaptive immune response.

> IB DP Biology Standard Level (2023 syllabus) — C3.2 Defence against disease · Explain · 4 marks

## Mark scheme (4 marks)

1. B lymphocytes produce / secrete antibodies (as plasma cells)
2. T lymphocytes do not produce antibodies; instead, T helper cells activate other immune cells (B cells and cytotoxic T cells) / coordinate the immune response
3. Cytotoxic T lymphocytes directly kill infected / abnormal cells (e.g. virus-infected cells or tumour cells) by inducing apoptosis / cell lysis
4. B lymphocytes respond to antigens that are free / extracellular, whereas T lymphocytes respond to antigens presented on cell surfaces (via MHC / major histocompatibility complex proteins)

## Key terms

- [B lymphocyte](https://www.gradenine.co.uk/glossary/b-lymphocyte)
- [T lymphocyte](https://www.gradenine.co.uk/glossary/t-lymphocyte)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-b-lymphocytes-and-t-fd6e1e26) · Published by Druglandscape Ltd.