Organisms in the Domains Bacteria and Archaea


Bacteria constitute a large domain of prokaryotic micro organisms, usually a few micrometers in length found in various shapes ranging from spheres, rods and spirals. The Archaea constitute a domain of single- cell micro organisms. The microbes are prokaryotes with no cell nucleus or any other membrane- bound organelles in the cells. Previously before further research, evolutionary history and biochemistry archaea were classified as bacteria and were referred to as archaebacteria.

Their similarities and differences can be analyzed in

  • Size and shape
  • Flagella
  • Reproduction and growth
  • Difference in Cell structure
  • Habitat

Size and shape

The Archaea and bacteria have a similar shape and size. They both are found as rods, spirals, spheres and plates.

Reproduction and growth

Both the Archaea and Bacteria reproduce asexually by a process called binary fission, fragmentation and budding, though the bacteria have a unique ability to form spores that remain over years but is not dormant in Archaea. The process of growth is in three phases; the first phase ie the lag phase when cells adapt to new environment, log phase which involves exponential growth and stationary phase when there are few or no nutrients.


Archaea survive in extreme and harsh conditions like hot spring, salty lakes, digestion guts of ruminants and humans. Bactaria meanwhile are found everywhere in soil, hot springs, organic matter and also radioactive waste.


Archaea came from bacterial type IV pili while bacteria originated from type III secretion system. Bacterial flagellum is stalk hollow like and is made up of sub units that are free to move up the central pole while Archaea flagella subunits are added on to the base.

Difference in cell structure

The cell structure of both is structurally the same with cell wall and use flagella to swim but the Achaea do not have membranes on the interior. Achaea have a slight difference in the fact that their cell wall do not have peptidoglycan and their cell membrane uses ether linked lipids unlike in bacteria that uses ester linked lipids.

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