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Both bacteria and Archaea were classified in a similar domain previously called Archaebacteria. However, at present, they are categorized into distinct domains. The three-domain concept was proposed by Carl Woese in which all the organisms were classified into three domains called Archaea, Bacteria, and Eukarya.

Bacteria and Archaea vary in the characteristic of membrane and cell wall and their composition of lipid. The differences between the Archaea and Bacteria are:

1. The cell wall of Archaea is offour types, that is, it can be composed of polysaccharides, pseudopeptidoglycan, surface-layer proteins, or glycoproteins. On the other hand, the cell wall of bacteria is formed of peptidoglycan.

2. The cell membrane of Archaea can be a lipid bilayer or monolayer. It comprisesphytanyl (hydrocarbon). The cell membrane of bacteria is a bilayer of lipids. It comprisesfatty acids.

3. The flagella of Archaea have evolved fromtype IV pili, while the flagella of bacteria have evolved fromtype III pili.