Final answer:
Red blood cells are responsible for delivering oxygen to the body's cells and removing carbon dioxide. Their biconcave shape and lack of a nucleus allow for increased oxygen transport efficiency.
Step-by-step explanation:
The main purpose of red blood cells (erythrocytes) is B. they are responsible for the delivery of oxygen to the cells. Red blood cells achieve this by containing a protein called hemoglobin, which has the ability to bind to oxygen in the lungs and transport it through the bloodstream to the body's cells. Once at the cells, hemoglobin releases the oxygen, which enters the cells to support their metabolic activity. Additionally, red blood cells also help remove carbon dioxide, a waste product of cellular metabolism, by carrying it from the cells to the lungs, where it is exhaled.
The structure of red blood cells enhances their oxygen-carrying capacity. Their biconcave shape increases the surface area for oxygen absorption and release. Moreover, the lack of a nucleus and organelles in mature red blood cells in mammals creates more space for hemoglobin, enabling them to transport more oxygen.