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

Which adaptation helps red blood cells absorb and release oxygen effectively?

1. Presence of a nucleus

2. Biconcave disc shape

3. High iron content

4. Flexible structure

The correct answer is: Biconcave disc shape

The biconcave disc shape of red blood cells is a crucial adaptation that enhances their ability to absorb and release oxygen efficiently. This unique shape increases the surface area-to-volume ratio, allowing for more hemoglobin to be exposed to the surrounding plasma, facilitating oxygen binding. Additionally, the biconcave form aids in the movement of red blood cells through the narrowest capillaries, ensuring that they can navigate the bloodstream effectively. This shape allows the cells to deform as they travel through these small vessels, ensuring that they can reach tissues where oxygen is required. Moreover, the thinness of the cell wall in this shape allows for rapid diffusion of oxygen in and out of the cell. While factors like iron content and flexibility also contribute to oxygen transportation, the biconcave shape is fundamental to the primary function of red blood cells in oxygen delivery throughout the body. The presence of a nucleus is not applicable, as mature red blood cells lack a nucleus to maximize space for hemoglobin. Flexibility does support their movement, but without the optimal shape, their efficiency in gas exchange would be compromised.