Title: Taxonomy - BIOLOGY JUNCTION
Headings: Taxonomy
Taxonomy
Taxonomy
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Taxonomy – study of classifying organisms
Reasons to Classify:
Early Taxonomy:
Taxonomic categories:
Basis for Modern taxonomy:
Modern Taxonomic System:
Phylogeny (evolutionary history):
Three Domain System:

Content: 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

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