Classification & Taxonomy

An organized system to classify all living things

Biology is the study of life…

• But how do we know something is “alive”?– Metabolism

• Consume molecules• Produce wastes• Exchange gases

– Reproduction– Cells– DNA

The Need for a Classification System…

• Organizing and categorizing all of the organisms that exist on earth today is quite a task!

A system of classification must be…

- organized and logic

- universal (used by all scientists)

• Our current system breaks down organisms into more & more closely-related groups until only one group is left…the “species”!

Taxonomy…

• Taxonomy is the study, practice, and science of the classificiation of organisms.

Binomial Nomenclature(“to name with 2 names”)

• Each species is named with 2 words– The first word is the “genus”– The second word is the “specific epithet”– When written together, this name is called the

“species”– Ex: Homo sapiens or Homo sapiens

• Homo = genus of humans• sapiens = specific epithet of humans• Note: genus is capitalized, other is not…both

underlined or italicized

Taxons

• Groups of related genera are classified together in the same family

• Groups of related families for an order• This follows the pattern…

Orders Class Phylum Kingdom

• We usually memorize these from the largest to smallest direction:– K P C O F G S

Test Yourself!Name the 7 major taxons in order…

• Kingdom• Phylum• Class• Order• Family• Genus• Species

Dichotomous Keys

• Rules:– Always start at clue set #1– One of the choices must be correct…the other

must be incorrect– Identify the correct one and go where it says– When creating a key, it is better to use

“is…is not” format for clues– Will always have one fewer clue than # of

objects

Dichotomous Key Example

• Example:

• 1. A. contains ink……………..…..go to 2

• B. does not contain ink………..go to 3

• 2. A. point made of metal………..pen

• B. point not made of metal……marker

3. A. made of plastic…..mechanical pencil

B. not made of plastic…...regular pencil

All organisms have been placed into one of 6 kingdoms.

• This is a generally agreed-upon standard, but is subject to change

• We have not always had 6 kingdoms, and some scientists use fewer or more

• What criteria are used to place an organism in a kingdom?

Basic Criteria for Kingdoms(The Big 5!)

• # of Cells– Unicellular or Multicellular

• Type of Cell– Prokaryotic or Eukaryotic

• Cell Wall– Yes or No

• Nutrition– Autotrophic or Heterotrophic

• Motility– Yes or No

Test Yourself!What do the following mean?

• Unicellular• Multicellular• Prokaryotic• Eukaryotic• Autotrophic• Heterotrophic• Motile• Nonmotile• Cell Wall

Bacteria

• K. Archaebacteria– Harsh environments– Methanogens (anerobic)– Thermophiles (high heat)– Halophiles (salt)

• K. Eubacteria– “common” bacteria– Ex: E.coli; Staphylococcus aureus

• The Big 5:– Unicellular– Prokaryotic

– The other 3 traits are variable… examples of bacteria exist for each trait

K. Protista

• The most diverse and oft-changing kingdom!

• The Big 5:– Unicellular***– Eukaryotic– The other 3 traits are

variable…protists of various types exhibit both versions.

K. Fungi

• Often seem plant-like…but cannot make food!

• The Big 5:– Multicellular– Eukaryotic– Cell wall – of chitin– Heterotrophic – absorb food– Nonmotile

K. Plantae

• Usually green due to chlorophyll

• The Big 5:– Multicellular– Eukaryotic– Cell wall – of cellulose– Autotrophic– Nonmotile

K. Animalia

• Large, motile creatures that eat!

• The Big 5:– Multicellular– Eukaryotic– No cell wall– Heterotrophic – ingest

food– Motile

Taxonomic Tree• Cladistics- classification system based on

phylogeny; assumes that as groups of organisms diverge and evolve from a common ancestral group, they retain derived traits.

• Cladogram is the diagram used to represent the phylogeny of a species based on those derived traits.

Taxonomic Tree

Which group of organisms are most closely related?

Butterflies, moths and flies

X Y Z

1. A. Is multicellular………………………………..go to 2 B. Is unicellular……………………….…………go to 3

2. A. Contains chlorophyll; is green…………….ChlorellaB. Contains erythrophyll; is red………………Hemalia

3. A. Cell is oblong with tiny cilia………………...ParameciumB. Cell is blob-like with slender extensions….Amoeba

The End