# Explain how the lymphatic system contributes to the maintenance of tissue fluid balance in the body.

> IB DP Biology Standard Level (2023 syllabus) — B3.2 Transport · Explain · 4 marks

## Mark scheme (4 marks)

1. Capillary blood pressure forces fluid (water, dissolved solutes, small proteins) out of capillaries into the interstitial space, forming tissue fluid
2. Not all tissue fluid is reabsorbed by the capillaries; excess fluid and large proteins that cannot re-enter capillaries are drained into blind-ended lymph capillaries
3. Lymph is transported along lymphatic vessels back towards the heart / returned to the blood at the subclavian veins
4. If lymph drainage fails / is blocked, tissue fluid accumulates causing oedema, demonstrating the essential role of the lymphatic system in maintaining fluid balance

## Key terms

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

## 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-the-lymphatic-system-contributes-4d06176c) · Published by Druglandscape Ltd.