The cellular structure of a Kryptonian is similar to that of humans. However, a certain chemical makeup in the ribosomes (organelles responsible for protein synthesis) is capable of absorbing solar energy and storing it. Once the ribosomes achieve saturation levels of this radiation, they begin to re-radiate the energy in the form of a bioelectric forcefield. Each individual cell within the field's radius becomes reinforced in such a way that the cells are not only protected from external harm, but internal forces as well. It is this last which is key to Superman's great powers. Since the individual cells are wholly invulnerable, they are capable of operating at levels of efficiency that would destroy normal humanoid cells. These "super-cells" lend an enhancing effect to all bodily systems