Classification

Classification of Organisms

Learning Goals:

  • Describe how organisms are classified based on characteristics.

  • Explain the three-domain system.

  • Use an evolutionary tree to describe relationships between organisms.

1. Linnaean Classification System

  • Developed by Carl Linnaeus in the 1700s.

  • Based on observable physical characteristics.

  • Organisms grouped into hierarchical categories:

Kingdom → Phylum → Class → Order → Family → Genus → Species
Mnemonic: King Phillip Came Over For Good Soup

  • Binomial naming system:

    • Each organism has a Genus name + Species name (e.g., Equus quagga, Ursus maritimus).

    • This name is unique to each species.

2. Advances Beyond Linnaeus

  • Modern classification uses:

    • Microscopes to study internal structures.

    • Biochemistry and DNA analysis to compare similarity between species.

3. Three-Domain System (Woese)

  • Developed using biochemical data (e.g., DNA, RNA).

  • Domains:

    1. Archaea – primitive bacteria, often in extreme environments (hot springs, salt lakes).

    2. Bacteria – true bacteria, e.g., gut bacteria in humans.

    3. Eukaryota – organisms with complex cells, includes:

      • Animals

      • Plants

      • Fungi

      • Protists (e.g., amoeba)

4. Evolutionary Trees

  • Show relationships between species.

  • Use data from:

    • Living organisms (DNA, characteristics).

    • Fossils for extinct species.

  • Interpretation:

    • Closely related species share a recent common ancestor.

    • More distantly related species share an earlier common ancestor.

✅ Key Points

  • Classification organizes the diversity of life.

  • Binomial nomenclature ensures a unique, standardized name for every species.

  • Three-domain system reflects evolutionary relationships.

  • Evolutionary trees visualize relatedness and ancestry.