Describe the function of red blood cells and how they are suited to their function.

The primary function of red blood cells (RBCs) is to transport oxygen around the body. They contain haemoglobin, which oxygen attaches to in order to form oxyhaemoglobin. RBCs are very small in size and are flexible, which allows them access through narrow capillaries to deliver oxygen throughout the body. They do not contain nuclei (nor do they contain mitochondria or ER), allowing for more haemoglobin to be packed into the cell and therefore more oxygen to be carried within the cell. The bioconcave shape of RBCs gives them a large surface area to volume ratio, which increases the capacity of oxygen to diffuse into the cell.