In contrast to this structural complexity, there is less diversity in the actual cell chemistry. All eucaryotes respire using , although yeast and some other eucaryotes can get along with glycolysis alone when is unavailable.

All eucaryotes have mitochondria, with obviously homologous enzymes for use in the citric acid cycle and respiration. Photosynthetic eucaryotes all have Photocenters I and II, and obtain reducing equivalents by decomposing water and releasing . (Among procaryotes, only blue-green algae have two-center photosynthesis using )

The differences between any procaryote and any eucaryote are far greater than between the most diverse of the eucaryotes: fungi and primates, redwood and dragonfly.