Eukaryotic cells are advanced cells that have, at minimum, a cellular membrane surrounding cytoplasm, a cytoskeleton and membrane-covered organelles. More advanced eukaryotic cells also contain a nucleus that protects genetic material.
Eukaryotic cells probably developed around 2 billion years ago. Scientists believe the first eukaryotes were some form of algae. These cells make up every advanced form of earthly life, from mosses and fungus to the human body. Unlike prokaryotic bacteria and even simpler viruses, eukaryotic cells are "factories" of life, with organelles that function to provide cellular energy, eliminate toxins, create proteins and reproduce. By specializing these tasks, the eukaryotic cell was able to function more efficiently than primitive prokaryotes, giving it an evolutionary edge and enabling it to form multicellular life forms.