# Describe the roles of the four main components of blood in the human body.

> Eduqas A-Level Biology — 2.1 Classification and biodiversity · Describe · 5 marks

> Blood is a specialised tissue that transports substances, protects the body against infection and helps repair damage to blood vessels.

## Mark scheme (5 marks)

1. Plasma transports substances such as nutrients, hormones, urea or antibodies (any one acceptable example)
2. Red blood cells contain haemoglobin which binds to / carries oxygen around the body
3. White blood cells defend against infection / fight pathogens
4. Platelets are involved in blood clotting when a blood vessel is damaged
5. Blood clotting (by platelets) allows the vessel to heal AND/OR prevents pathogens entering the bloodstream through the wound

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-roles-of-the-four-c68f63d6) · Published by Druglandscape Ltd.