The distinction between prokaryotes and eukaryotes is the deepest division in the realm of life on Earth. Together, they include every life form ever discovered. Though the two groups share a common ancestry, there are basic differences between them. Eukaryotes have nucleated cells and identifiable cell structures called organelles, while prokaryotes are more variable in their cellular structure and lack a discrete nucleus, according to About.com.
The three domains into which life is divided are Eukaryota, Archaea and Eubacteria. Archaea and Eubacteria are both prokaryotes. Eukaryota includes all plants, animals and fungi. Every large life form on Earth is a eukaryote, and the bulk of Earth's microbes are prokaryotes. Despite the physical size of eukaryotic organisms, the biochemical diversity of this domain is limited. Almost all eukaryotes derive energy either directly or indirectly from the sun. Plants photosynthesize, animals eat plants or plant-eating animals, and fungi efficiently decompose the remains of the other two kingdoms, explains the College of Computer, Mathematical and Natural Sciences.
Prokaryotes have evolved not just photosynthesis, primarily among the cyanobacteria, but decomposition and even the ability to extract chemical energy from rocks and geothermal vents. Such eukaryotes that are able to live near these environments do so mainly by subsisting on a food chain with either bacteria or archaea at the bottom of it.