18.2.1

3-Domain Classification System

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New Classification Systems

Technological advancements have led to new, more accurate classification systems.

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Technological advancements

  • New technologies have allowed extensive sequencing of the DNA and proteins of organisms.
  • More closely-related organisms have DNA with a more similar base sequence and proteins with a more similar amino acid sequence.
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3-domain system

  • Carl Woese proposed the 3 domain system. This classifies organisms based on chemical analysis.
  • The 3 domains are:
    • Archaea - primitive bacteria.
    • Bacteria - true bacteria.
    • Eukaryota - organisms possessing complex sub-cellular structures (protists, fungi, plants & animals).
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Viruses

  • Viruses are not classified as living so they do not feature in the 3-domain system.
    • Viruses are not seen as living as they rely on other cells to reproduce and have no metabolism.
  • Virus classification is based on their:
    • Nucleic acid (DNA or RNA).
    • Whether these nucleic acids are single- or double-stranded.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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