AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Arteries carry blood away from the heart under high pressure, so the blood flows continuously forward — no valves are needed.
Veins carry blood back to the heart under low pressure. Without valves, blood could flow backwards. The valves in veins ensure blood flows only in one direction — towards the heart.
Source: Chapter 5, Section 5.4.1 – The tubes – blood vessels
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The textbook directly states: arteries have thick, elastic walls (to withstand high pressure) while veins have valves because blood is no longer under pressure and needs to be prevented from flowing backwards. Examiners expect both parts — why arteries don't need valves AND why veins do — for full 2 marks. Use keywords: high pressure (arteries) and one direction / prevent backflow (veins).