Taxonomy
All Materials © Cmassengale

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