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Carolus Linnaeus

Taxonomy – study of classifying organisms

  • Taxonomists are scientists who study classifying
  • Taxon ( taxa-plural) is a category into which related organisms are placed

Reasons to Classify:

  • Shows evolutionary relationships
  • Accurately & uniformly names organisms
  • Prevents misnomers such as starfish & jellyfish that aren’t really fish
  • Uses same language (Latin) for all names
  • Prevents duplicated names because all names must be approved by International Naming Congresses (International Zoological Congress)
  • Naming rules are followed called the International Code for Binomial Nomenclature

Early Taxonomy:

  • Aristotle was the first taxonomist dividing organisms into land, sea, & air dwellers
  • John Ray was the first to use Latin for naming
  • Linnaeus developed the modern system of naming known as binomial nomenclature, a two-word name (Genus & species)
  • Scientific names should be italicized in print or underlined when writing
  • Always capitalize the genus name, but write the species in lower case
  • The scientific name for man is Homo sapiens
  • The genus name may be abbreviated, but not the species (H. sapiens)

Taxonomic categories:

  • Linnaeus placed organisms into related groups called taxa (taxon-singular) based on their morphology (similar structure & function)
  • The broadest taxon is called the kingdom
  • Linnaeus put all organisms into one of two kingdoms — Plantae or Animalia
  • The other six taxa from broadest to most specific are — Phylum, Class, Order, Family, Genus, & species
  • A sentence to help remember these taxa is — “King Phillip Came Over For Gooseberry Soup.”
  • Each taxa is a proper noun &should be capitalized except species
  • Each level or taxon groups together organisms that share more characteristics than the level above

  • Botanists use the term division instead of phylum for classifying plants
  • Plant species are subdivided into varieties, while bacteria are subdivided into strains

Basis for Modern taxonomy:

  • Modern taxonomists classify organisms based on their evolutionary relationships
  • Homologous structures have the same structure, but different functions & show common ancestry
  • The bones in a bat’s wing, human’s arm, penguin’s flipper are the same (homologous), but the function is different

  • Analogous structures have the same function, but different structures & do not show a close relationship (insect wing & bird’s wing)
  • Similarity in embryo development shows a close relationship (vertebrate embryos all have tail & gill slits)

  • Similarity in DNA & amino acid sequences of proteins show related organisms

Modern Taxonomic System:

  • Modern taxonomy uses six kingdoms — Archaebacteria, Eubacteria, Protista, Fungi, Plantae, & Animalia
  • Archaebacteria & Eubacteria are unicellular prokaryotes lacking a nucleus, while Protista, Fungi, Plantae, & Animalia are all eukaryotes with a nucleus & membrane-bound organelles
  • All members of Plantae & Animalia are multicellular organisms
  • Fungi & Animalia are heterotrophs, while Plantae are all autotrophs capable of making their own food
  • Archaebacteria live in harsh environments like very salty lakes; intestines of mammals; and hot, sulfur springs & may be autotrophs or heterotrophs
  • Eubacteria are true bacteria some of which cause disease
  • Protista are mainly unicellular with a few multicellular organisms and may be autotrophic (Euglena) or heterotrophic (Ameba)
  • Fungi include multicellular mushrooms, mold, unicellular yeast, etc. & are absorptive heterotrophs (digest food & then absorb it)
  • Animalia are ingestive heterotrophs that take in food & then digest it inside their multicellular bodies.
  • Plantae includes all plants & are the only all multicellular, autotrophic kingdom

Phylogeny (evolutionary history):

  • Phylogenetic trees are branching diagrams showing how organisms are related
  • Also called family trees
  • Fossil records help establish relationships on a phylogenetic tree
  • Organizes living things based on their evolution (systematics)
  • Common ancestor is shown at the base of the tree
  • Most modern organisms shown at tips of branches
  • Each time a branch divides into a smaller branch, a new species evolves

  • Cladograms shows how organisms are related based on shared, derived characteristics such as feathers, hair, scales, etc.

Three Domain System:

  • Based on comparing sequences of ribosomal RNA in different organisms to determine ancestry
  • All organisms placed into three broad groups called domains
  • Domain Archaea (kingdom Archaebacteria) contains chemosynthetic bacteria living in harsh environments
  • Domain Bacteria (kingdom Eubacteria) contains all other bacteria including those causing disease
  • Domain Eukarya (kingdoms Protista, Fungi, Plantae, & Animalia) contains all eukaryotic organisms