OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How does the flexibility of red blood cells assist their function?

1. Allows them to hold more oxygen

2. Helps them to pass through capillaries

3. Increases their lifespan

4. Enhances their ability to absorb nutrients

The correct answer is: Helps them to pass through capillaries

The flexibility of red blood cells is crucial for their function, particularly because it enables them to pass through narrow capillaries. Capillaries are tiny blood vessels that are often only slightly wider than a red blood cell itself. As red blood cells navigate the circulatory system, they must squeeze through these small vessels, which can be challenging given their relatively large size compared to the diameter of capillaries. Their biconcave shape, combined with their flexible cell membrane, allows them to deform and bend without breaking, facilitating smooth passage even in the smallest blood vessels. This flexibility is essential for ensuring that oxygen, which red blood cells transport from the lungs to tissues, can be delivered efficiently throughout the body. If red blood cells were rigid, they would struggle to maneuver through capillaries, leading to inadequate oxygen delivery and potential blockages in the microcirculation. Consequently, the ability to pass through capillaries unhindered is a key factor in the effectiveness of red blood cells in maintaining proper oxygen supply to various tissues.