Biology: classification: domains
Tutoring biology, classification comes up. The tutor mentions domains in biology.
When I was in high school, the classification system in biology started with kingdom, so far as I learned. Nowadays, a level has been introduced above kingdom: the domain.
In biology there are three domains: Archae, Bacteria, and Eukarya (aka Eukaryota). Domains are defined based on cellular differences.
Eukarya includes eukaryotic cells: cells that have a nucleus. The kingdoms Protista, Fungi, Plantae, and Animalia are all under Eukarya. Archae and Bacteria contain one kingdom each: Archae contains Archaebactera, while Bacteria contains Eubacteria. It seems that, because of the specificity of those relationships, some people refer to Archae as Archaebacteria and Bacteria as Eubacteria.
Eubacteria includes “common” bacteria that live where people can; archaebacteria, on the other hand, live in extreme environments thought to be otherwise “unlivable,” such as around volcanic activity, in very salty ponds, or in deep layers of decaying organic material where no oxygen is present.
The classification differences between Eubacteria and Archaebacteria, as I understand, are due to chemical aspects of the cell wall and cell membrane:
- Archaebacteria: no peptidoglycan in cell wall; ether linkage in cell membrane.
- Eubacteria: peptidoglycan in cell wall; ester linkage in cell membrane.
Source:
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.