Domains

Definition

Domains are the highest taxonomic rank in the hierarchical biological classification system. They categorize life into three broad groups: Archaea, Bacteria, and Eukarya.

5 Must Know Facts For Your Next Test

1. The domain system was introduced by Carl Woese in 1990.
2. Archaea and Bacteria are both prokaryotic domains, meaning their cells do not have a nucleus.
3. Eukarya includes all eukaryotic organisms, which have cells with a nucleus.
4. Domains are divided into kingdoms, which are further subdivided into phyla, classes, orders, families, genera, and species.
5. Molecular analysis of ribosomal RNA was crucial in distinguishing between the three domains.

Review Questions

• What are the three domains of life?
• Which domain includes organisms with cells that have a nucleus?
• Who introduced the current domain system?

Related terms

Kingdom:

A rank below domain used to classify organisms into larger groups such as Plantae or Animalia.

Prokaryote: An organism whose cells lack a nucleus and other organelles enclosed within membranes.

Eukaryote: An organism whose cells contain a nucleus and other organelles enclosed within membranes.