Final answer:
The advantage of a mature red blood cell having a flattened shape rather than a spherical shape is that it provides more surface area for gas exchange compared to its volume.
Step-by-step explanation:
The advantage of a mature red blood cell having a flattened shape rather than a spherical shape is that it provides more surface area for gas exchange compared to its volume. The biconcave shape of red blood cells optimizes the ratio of surface area to volume, allowing for efficient exchange of respiratory gases. This shape also enables the cells to fold up as they move through narrow blood vessels, ensuring they can reach all cells in the body.