Biology 20 – Unit B: Classifying and Naming Organisms

Classifying and Naming Organisms

The Classification of Organisms

  • Taxonomy: The practice of classifying living things. It is useful for scientists to classify organisms into groups.

Historical Classification

  • Aristotle:
    • The first to attempt to classify life.
    • In his time, about 1000 species had been identified.
    • He placed them into two groups: plants and animals.
    • He called each group a kingdom, later known as Kingdom Plantae and Kingdom Animalia.
    • He further grouped them according to size and habitat (land, air, water).

Six Kingdoms of Life

  • Today, living things are organized into six kingdoms.
Kingdom Archaea (or Archaebacteria)
  • Single-celled organisms lacking a nucleus (prokaryotes).
  • Bacteria capable of living in extreme environments (extremophiles).
  • Examples:
    • Salt lakes
    • Hot springs
    • Underwater thermal hot vents
  • Example Species:
    • Methanococcus jannaschii
    • Extreme halophiles
Kingdom Bacteria (or Eubacteria)
  • Single-celled organisms lacking a nucleus.
  • Very diverse.
  • Can exist in a wide range of habitats.
  • Examples:
    • Streptococcus pyogenes
    • Cyanobacteria
Kingdom Protista
  • Have nuclei (eukaryotes).
  • Can be unicellular or multicellular.
  • Some can photosynthesize, while others need to eat.
  • Some decompose and then absorb their food. *Examples:
    • Euglena
    • Trypanosoma (causes African Sleeping Sickness)
Kingdom Fungi
  • Obtain food by secreting digestive enzymes and then absorbing the digested molecules.
  • Do not have chloroplasts; do not photosynthesize.
  • Both multicellular and unicellular fungi.
  • Examples:
    • Bioluminescent fungi (Brazil)
    • Maiden’s Veil Fungi
Kingdom Plantae
  • Organisms that photosynthesize.
  • Do not move and are multicellular.
  • Examples:
    • Aloe Vera
    • Palm Tree
Kingdom Animalia
  • Ingest their food.
  • Most are motile.
  • Example:
    • Star-nosed mole

The Three Domains of Life

  • A level above kingdoms called domains.
  • Three domains: Bacteria, Archaea, and Eukarya.
  • Based on the cellular composition of organisms.

Levels of Classification

  • Carolus Linnaeus (1707-1778): Further subdivided each kingdom into smaller groups.
  • Classification Levels:
    • Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
  • Example (Humans):
    • Eukarya, Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, sapiens
  • Mnemonic:
    • Dashing King Philip Came Over For Good spaghetti

Binomial Nomenclature

  • Linnaeus's simplification: A two-name system.
    • The first name is the organism's genus, and the second is its species.
    • The first letter of the genus is capitalized, but the species is lower case.
    • Both are italicized or underlined.
    • Example: Homo sapiens
    • Latin is used to name the species (universal scientific language).

Dichotomous Keys

  • Dichotomous key: Classification manuals to identify organisms.
  • Arranged in steps with two statements for each step.
  • Always begin by choosing from the first pair of descriptions and then following the key from there.