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

> WJEC A-Level Biology (Wales) — 2.1 Classification and biodiversity · Describe · 5 marks

> Blood is a vital tissue that carries out several important functions in the human body. It is made up of four main components, each with a specific role.

## Mark scheme (5 marks)

1. Plasma transports substances such as nutrients, hormones, urea or antibodies around the body (accept any one valid example)
2. Red blood cells contain haemoglobin which binds to / carries oxygen to the body's cells
3. White blood cells protect against infection / fight pathogens
4. Platelets are involved in blood clotting / stick together to block a cut/wound
5. Blood clotting (by platelets) prevents pathogens from entering the blood vessel / allows the vessel to heal

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