OCR GCSE Biology 2025 – 400 Free Practice Questions to Pass the Exam

Veins are characterized by having valves to prevent backflow of blood, which is crucial for maintaining unidirectional flow back to the heart, especially in the limbs where blood must travel against gravity. The presence of these valves is a vital adaptation that assists in ensuring that blood moves efficiently despite the lower pressure in veins compared to arteries.

While arteries must handle higher pressure and thus have thicker walls, veins are equipped to manage the slower flowing blood returning from the body. The valves in veins close when the blood tries to flow backward, thereby preventing any potential pooling or reflux of blood. This mechanism helps maintain the circulation of blood and supports overall cardiovascular health.

Additionally, veins typically carry deoxygenated blood back to the heart (except for the pulmonary veins, which carry oxygenated blood from the lungs), and they often have a larger lumen compared to arteries to accommodate the volume of blood being returned.