Three domain system of classification by Carl Woese
In 1990, American microbiologist Carl Woese suggested that there are two separate groups of prokaryotes i.e., Archaea and Bacteria. On this basis, he classified living organisms into three domains:
- Domain Archaea
- Domain Bacteria
- Domain Eukarya
According to his three-domain system:
- Domain Archaea and Domain Bacteria contain prokaryotes, but they differ in a number of features.
Now biologists believe that Archaea and Bacteria evolved independently from some common ancestor. Molecular evidence suggests that archaea are more closely related to eukaryotes than to bacteria.
In other words, Eukarya evolved from Archaea, after archaea split off from the Bacteria (Figure 1.1).
Domain Archaea
In the five-kingdom system, this domain was included in kingdom Monera.
- The name Archaea comes from the Greek word archaios (“ancient”).
- They are prokaryotes which diverged from bacteria in very ancient times.
- Individual archaeans range from 0.1 μm to over 15 μm in diameter.
- Some form aggregates or filaments up to 200 μm in length.
- They occur in various shapes, such as spherical, rod-shape, spiral, lobed, or rectangular.
Reproduction in Archaea:
- Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding.
- Mitosis and meiosis do not occur in archaea.
How Are Archaea Unique?
Cell Membrane
Their cell membrane contains lipids with ether-linkage between glycerol and fatty acid chains.
Three domain system of classification by Carl Woese In 1990, American microbiologist Carl Woese suggested that there are two separate groups of prokaryotes i.e., Archaea and Bacteria. On this basis, he classified living organisms into three domains: Domain Archaea Domain Bacteria Domain Eukarya According to his three-domain system: Domain Archaea and Domain Bacteria contain prokaryotes, but they differ in a number of features. Now biologists believe that Archaea and Bacteria evolved independently from some common ancestor. Molecular evidence suggests that archaea are more closely related to eukaryotes than to bacteria. In other words, Eukarya evolved from Archaea, after archaea split off from the Bacteria (Figure 1.1). Domain Archaea In the five-kingdom system, this domain was included in kingdom Monera. The name Archaea comes from the Greek word archaios (“ancient”). They are prokaryotes which diverged from bacteria in very ancient times. Individual archaeans range from 0.1 μm to over 15 μm in diameter. Some form aggregates or filaments up to 200 μm in length. They occur in various shapes, such as spherical, rod-shape, spiral, lobed, or rectangular. Reproduction in Archaea: Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding. Mitosis and meiosis do not occur in archaea. How Are Archaea Unique? Cell Membrane Their cell membrane contains lipids with ether-linkage between glycerol and fatty acid chains.