In-Depth Notes on Taxonomy and Classification Systems (Bio Unit 2 Quest 1)

Taxonomic Systems

  • Carl Linnaeus (1707–1778):

    • Swedish botanist
    • Developed our modern biological classification system.
    • Based on physical and structural features of organisms.
    • Emphasized that organisms with more features in common are closely related.

  • Binomial Nomenclature:

    • A naming system for organisms using two Latin words.
    • First part: Genus (capitalized).
    • Second part: Species (lowercase, never used alone).
    • Example:
      • Castor canadensis:
      • Castor: "beaver" (genus)
      • canadensis: "from Canada" (species).
    • Indicates similarities in anatomy, embryology, and evolutionary ancestry.
    • Example of related species:
    • Ursus americanus (North American black bear) and Ursus horribilis (grizzly bear) belong to the same genus (Ursus).

Levels of Classification

  • Seven main levels or taxa (singular: taxon):

    1. Kingdom
    2. Phylum
    3. Class
    4. Order
    5. Family
    6. Genus
    7. Species

  • Kingdoms:

    • Originally comprised only two kingdoms: Plantae and Animalia.
    • Protista was added later for unicellular organisms.
    • Monera introduced for prokaryotes (organisms lacking a true nucleus).

Five-Kingdom Classification System

  • Proposed by Robert Whittaker in 1969:

    • Animalia
    • Plantae
    • Fungi
    • Protista
    • Monera

  • Archaebacteria vs Eubacteria:

    • Archaebacteria:
    • Unique prokaryotic microorganisms that thrive in extreme environments.
    • Possess different ribosomal structures compared to Eubacteria.
    • Eubacteria:
    • True bacteria with peptidoglycan in their cell walls.

Six-Kingdom System

  • Proposed by Carl Woese:
    • Animalia
    • Plantae
    • Fungi
    • Protista
    • Eubacteria
    • Archaebacteria

Phylogeny

  • Definition: The history of the evolution of species or groups of organisms.
  • Represented in diagrams known as phylogenetic trees showing evolutionary relationships.
  • Recent DNA studies indicated that some genes of Archaebacteria are more similar to those in eukaryotes (humans) than to Eubacteria.

Dichotomous Keys

  • Dichotomous key: A tool for identifying organisms through a series of choices.
  • Provides a systematic approach to classification based on distinct characteristics, leading to the identification of an organism.
  • Example: Identification of whale species using body structure as a basis for classification.