TAXONOMY

Species of OrganismsSpecies of Organisms

•There are 13 billion known There are 13 billion known species of organismsspecies of organisms

•This is only 5% of all This is only 5% of all organisms that ever lived!!!!!organisms that ever lived!!!!!

•New organisms are still New organisms are still being found and identifiedbeing found and identified

Taxonomy

• Classification:Classification: the arrangement of the arrangement of organisms into orderly groups based organisms into orderly groups based on their similaritieson their similarities

• Taxonomy: the study of classifying organisms

• Taxonomists: scientists who study classifying

• Taxon (taxa-plural): category into which related organisms are placed

Reasons to Classify• Shows evolutionary relationships• Accurately & uniformly names organisms• Prevents misnomers (starfish & jellyfish

aren’t really fish)• Uses same language (Latin) for all names• Prevents duplicated names b/c all names

must be approved by International Naming Congresses (International Zoological Congress)

• Naming rules are followed: International Code for Binomial Nomenclature

Early Taxonomy• Aristotle: Greek philosopher; first to

classify organisms; grouped into plants and animals – then into habitat

• John Ray: first to use Latin for naming• Linnaeus: Swedish botanist; first to classify

based on structure; developed modern system of naming known as binomial nomenclature; Systema Naturae (two-word name: Genus and species); “Father of Taxonomy”

Rules for Naming

• Scientific names should be italicized in print or underlined when written

• Always capitalize the genus name, and lower case species

• Scientific name for man is Homo sapiens

• Genus may be abbreviated, but not the species (H. sapiens)

Taxonomic Categories• Linnaeus placed organisms into related

groups called taxa based on their morphology (similar structure & function)

• The broadest taxon is called the domain – then 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

• “King Phillip Came Over For Gooseberry Soup”

Taxonomic Categories contd.

• Each 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

DomainsDomains• BroadestBroadest, most inclusive taxon, most inclusive taxon• ThreeThree domains domains• Archaea and EubacteriaArchaea and Eubacteria are are

unicellular prokaryotes (no unicellular prokaryotes (no nucleus or membrane-bound nucleus or membrane-bound organelles)organelles)

• EukaryaEukarya are more complex and are more complex and have a nucleus and membrane-have a nucleus and membrane-bound organellesbound organelles

Domain Eukarya is Domain Eukarya is Divided into KingdomsDivided into Kingdoms

•ProtistaProtista (protozoans, algae…) (protozoans, algae…)•FungiFungi (mushrooms, yeasts …) (mushrooms, yeasts …)•PlantaePlantae (multicellular plants) (multicellular plants)•AnimaliaAnimalia (multicellular animals) (multicellular animals)

TaxonsTaxons

•Most Most generagenera contain a contain a number of similar speciesnumber of similar species

•The genus The genus HomoHomo is an is an exception (only contains exception (only contains modern humans)modern humans)

•Classification is based on evolutionary relationshipsevolutionary relationships

Species• What makes a species?

– Common descent: have a common ancestor– Smallest distinct groupings: chromosomal and

molecular characteristics– Reproductive community: must exclude

members of other species; for sexually reproducing populations, interbreeding is critical for maintaining a reproductive community

– Geographic range: distribution through space (cosmopolitan: large area; endemic: restricted distribution)

– Evolutionary duration: distribution through time

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

Homologous Stuctures

Basis for Modern Taxonomy contd.

• 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 or proteins show related organisms

Embryo Development

Modern Taxonomic System

• Modern taxonomy uses six kingdoms Archaebacteria, Eubacteria, Protista, Fungi, Plantae, & Animalia

• Archaebacteria & Eubacteria are unicellular prokaryotes lacking a nucleus

• Protista, Fungi, Plantae, & Animalia are all eukaryotes with a nucleus & membrane-bound organelles

Modern Taxonomic System contd.

• 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 (very salty lakes, intestines of mammals, hot sulphur springs); may be autotrophs or heterotrophs

Modern Taxonomic System contd.

• Eubacteria: true bacteria; some cause disease

• Protista: mainly unicellular; may be autotrophic (Euglena) or heterotrophic (Amoeba)

• Fungi: include multicellular mushrooms, mold, unicellular yeast, etc.; absorptive heterotrophs (digest food & then absorb it)

Modern Taxonomic System contd.

• Animalia: ingestive heterotrophs; multicellular

• Plantae: include all plants; all multicellular; all autotrophs

Phylogeny (Evolutionary History)

• Phylogenetic trees: branching diagrams showing how organisms are related; “family tree”

• Fossil records help establish relationships on a phylogenetic tree

• Organizes living things based on their evolution

• 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

Phylogenetic Tree

Cladograms

• Cladogram: show how organisms are related based on shared, derived characteristics such as feathers, hair, scales, etc.

Cladograms

Dichotomous KeyingDichotomous Keying

•Used to identify organismsUsed to identify organisms•Characteristics given in Characteristics given in pairspairs•Read both characteristicsRead both characteristics

and either go to another set and either go to another set of characteristics of characteristics OROR identify identify the organismthe organism

Example of Example of Dichotomous KeyDichotomous Key

• 1a Tentacles present – Go to 21a Tentacles present – Go to 2• 1b Tentacles absent – Go to 31b Tentacles absent – Go to 3• 2a Eight Tentacles – Octopus2a Eight Tentacles – Octopus• 2b More than 8 tentacles – 32b More than 8 tentacles – 3• 3a Tentacles hang down – go to 43a Tentacles hang down – go to 4• 3b Tentacles upright–Sea 3b Tentacles upright–Sea

AnemoneAnemone• 4a Balloon-shaped body–Jellyfish4a Balloon-shaped body–Jellyfish• 4b Body NOT balloon-shaped - 54b Body NOT balloon-shaped - 5