If we had a cubic millimeter of blood, there would be 5x10^6 red blood cells, which is 5 million red blood cells per cubic millimeter of blood. Which means 5 trillion cells in a 5 litre circulatory system.
- The shape is described as a Bioconcave disc. This shape gives you short diffusion distance for oxygen so we get fast diffusion.
- There is no nucleus in the red blood cell, which means more space for haemaglobin and no mitochondria means that the red blood cells will not use up the oxygen it is transporting.
- The presence of haemaglobin - haemaglobin is able to carry oxygen and there are millions of haemaglobin molecules (5x10^6) per cell. Each one carrying 4 oxygen molecules.