# Explain how the components of blood are adapted to carry out their functions in the transport of oxygen and defence against pathogens.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.2 Heart, blood and blood vessels · Explain · 5 marks

> Blood is a tissue made up of several components, each with a specific function in the body.

## Mark scheme (5 marks)

1. Red blood cells contain haemoglobin which combines with oxygen to form oxyhaemoglobin
2. Red blood cells have no nucleus, allowing more space for haemoglobin / to carry more oxygen
3. Red blood cells have a biconcave shape, which increases surface area for gas exchange / diffusion of oxygen
4. White blood cells defend against pathogens by engulfing them (phagocytosis) or by producing antibodies
5. Plasma transports dissolved substances including carbon dioxide / glucose / hormones / urea around the body

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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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