Which feature of red blood cells primarily increases the surface area to volume ratio to aid diffusion?

• A. Increases SA:Vol ratio
• B. Increases energy production
• C. Maintains nucleus
• D. Regulates blood pH

Answer: (B)

Red blood cells are shaped as tiny biconcave discs, a design that increases their surface area relative to volume. This extra surface area lets gases cross the cell membrane more quickly, speeding the diffusion of oxygen into and carbon dioxide out of the cell as hemoglobin carries the gases. Energy production isn’t the driver here—mature red blood cells actually lack mitochondria and rely on glycolysis for energy, so diffusion efficiency comes mainly from the increased surface area provided by the biconcave shape rather than metabolic activity. Maintaining a nucleus isn’t the feature that boosts diffusion, and regulating blood pH is a broader function of blood chemistry, not the primary reason for the cell’s shape.