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Lesson: Chapter 13 — The Living World

13.1. The three domains 1 of 5

Three domains of life

Various scientists have put forward classification systems from history to the present day. Two of them are still accepted.

Robert Whittaker, 1969

Put forward the five kingdom classification, which is accepted to this day.

Carl Woese, 1990

Introduced the domain as a level above the kingdoms, and put forward the three domain classification.

The three domains

  1. Domain Archaea
  2. Domain Bacteria
  3. Domain Eukarya

Figure to be added

Figure 13.3 — the three domain classification: Archaea and Bacteria branching off first, with Protista, Fungi, Plantae and Animalia sitting inside Eukarya.

What does the dividing is a cell, not a habit

The chief thing separating the three domains is the nucleus. Archaea and Bacteria are prokaryotic — no organised nucleus. Eukarya are eukaryotic — an organised nucleus is present.

Which raises a question: if Archaea and Bacteria are both prokaryotic, what separates them? The next two pages are about that.