And this is another byproduct of the fact that they do not have any organelle. They are extremely specialized to carry out one purpose, and that is to actually carry those oxygen molecules from one cell to a different cell in our body. Now, let's move on to leukocytes. Now, our red blood cells make up the predominant portion of the cells of our blood. Leukocytes only make up about 1% of the cells of our blood. But when we have some type of infection, this number can greatly increase.