How is a red blood cell well suited to the transport oxygen

Q:

How is a red blood cell well suited to the transport of oxygen?

A:

At the level of the cell, red blood cells lack organelles, cell nuclei, and mitochondria. This means that they cannot produce RNA and cannot replicate themselves; however, it also means that they do not need to consume as much oxygen as other cells and as such they are able to carry oxygen to other cells. In addition, the red blood cell's concave "donut" shape allows it to maximize oxygen transfer with other tissue, and the red blood cell is highly flexible, which allows it to pass through small capillaries in and out of the lungs to collect oxygen.

Another chief aspect of the red blood cell's ability to transport oxygen is at the molecular level. The key is the molecule hemoglobin, a highly specialized, three-dimensional protein. This molecule is also responsible for red blood cells' red color. Hemoglobin uses ionized (charged) iron to bind oxygen atoms. Each hemoglobin molecule is able to bind up to four oxygen molecules (`O_2`) via four specialized heme complexes.