IGCSE Biology glossary
Vein
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Definition
A blood vessel that carries blood towards the heart, usually deoxygenated (except the pulmonary vein). Veins have thinner walls than arteries, a wider lumen, and contain valves to prevent backflow of blood.
What to include in an exam answer
Veins carry blood TO the heart. They have valves to prevent backflow because blood pressure is low. In comparison tables, veins are the ones with valves, wide lumen and thin walls.
Example in context
Explain why veins contain valves but arteries do not (2 marks): Blood pressure in veins is low, so blood may flow backwards. Valves prevent this backflow. Arteries have high blood pressure which keeps blood moving forward, so valves are not needed.
Related syllabus topic
Transport in animals