So as the red blood cells with the biconcave shape squeeze through the capillaries surrounding our tissues and cells, we basically exchange that oxygen for carbon dioxide. Now, the next important structure point of our red blood cell is the fact that they do not actually have any organelles. So they don't have nuclei, they don't have mitochondria or any other organelle, for that matter. Now, why is that important? What is the relevance of that property? Well, because they don't have any organelles.