Bacteria and archaea are microorganisms of prokaryotic morphology. The cells of these organisms do not have a nucleus or membranous organelles inside. However, both are so different that they form completely separate domains, the Bacteria Domain and the Archaeal Domain.
Archaea were formerly known as Archaebacteria and were considered a group of bacteria, albeit with different biochemical characteristics that made them form a kingdom of their own, the Monera Kingdom within the Prokaryota superrealm.
It was later discovered, thanks to studies of genetic material, that the evolution of archaebacteria and bacteria was independent, so the archaea could no longer be considered as a group of bacteria. Thus was born the current classification of three domains: Archea, Bacteria S eukarya.
Archaea and bacteria are morphologically very similar, but archaea are closer to eukaryotes, especially some genes and metabolic pathways of transcription and translation.
Some notable differences:no spore-reproducing archaea species are known, unlike the Bacteria and Eukarya domains. Nor any where there is sexual reproduction. They reproduce mainly by binary fission, budding or fragmentation. Another unique biochemical feature of archaea is a lipid ethers of its cytoplasmic membrane which is not observed in the other domains. Archaea can inhabit a wide spectrum of environments, many of them being extremophiles, loving extreme environments in temperature, pH or salinity. But they were found in almost any habitat, being very numerous in the oceans, so much so that among the plankton archaea one of the most numerous organisms on the planet can be found. In the human intestine, as part of the flora, there are methanogenic archaea, organisms that require a strictly anaerobic environment and that produce methane, the main component of natural gas, which is why it is believed to play a very important role in the degradation of organic matter in nature. Another characteristic that differentiates an archaea from a bacterium is in the photosynthetic metabolic pathways. There are bacteria and eukaryotes that can perform oxygenated photosynthesis; however, there are archaea capable of photosynthesis but not oxygenated that do not produce Otwo. Most photosynthetic archaea are photoheterotrophs. There are also archaea that fix atmospheric CO2s, although they do not use solar energy to do so.