Three Domains of Classification – Class 11 | Chapter – 2 | Short Notes Series PDF

Three Domains of Classification: All organisms are now classified into three major domains. The Three Domain System, developed by Carl Woese in 1990, is a system for classifying biological organisms

Before Woese’s discovery of archaea as distinct from bacteria in 1977, scientists believed there were only two types of life: eukarya and bacteria.

Three Domains of Classification

The highest ranking previously used had been “kingdom,” based on the Five Kingdom system adopted in the late 1960s. This classification system model is based on principles developed by Swedish scientist Carolus Linnaeus, whose hierarchical system groups organisms based on common physical characteristics.

Archaea:

1. The domain Archaea contains organisms that included early prokaryotes that live in extreme environments called archaebacteria.
2. It includes the kingdom Archaebacteria.
3. Examples: Sulfolobus tokodaii, Thermosphaera aggregans.

Bacteria:

1. The domain Bacteria contained typical prokaryotes that lack membrane-bound cell organelles.
2. It includes the kingdom Eubacteria.
3. Examples: Escherichia coli, Lactobacillus acidophilus

Eukarya:

• The domain Eukarya contains eukaryotic organisms. It includes the kingdoms Protista, Fungi, Plantae and Animalia.
• Examples are All eukaryotic organisms like chloroplast and mitochondria.

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