Classification
 The arrangement of organisms into orderly groups based on their similarities
 The branch of biology that involves classifying is called taxonomy
 Taxonomists are scientists that identify & name organisms
Benefits of Classifying
 Accurately & uniformly names organisms
 Uses same language, Latin or some Greek, for all names
Basis for Classification
 Structural similarities, likely evolved from common ancestor Ex: lynxes and
bobcats
 If number & structure of chromosomes are similar, may have common
ancestor Ex: cabbage, cauliflower and kale -> almost identical chromosome
structure
 Similar organisms have similar DNA sequence Ex: giant panda is more closely
related to a bear than the red panda
Classification Groups
 Taxon (taxa-plural) is a category into which related organisms are placed
 There is a hierarchy of groups (taxa) from broadest to most specific
 Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
(Dapper King Phillip Came Over From Germany Singing)
Domains
 Broadest & most inclusive taxon
 3 domains
 Archae & Eubacteria are unicellular prokaryotes (no nucleus or membrane
bound-organelles)
 Eukarya are more complex (have a nucleus & are membrane-bound organelles)
Archaea
 1st cells to evolve
 live in harsh environments
 found in sewage treatment plants, thermal or volcanic vents, hot springs or
geysers that are acid or very salty H2O such as the Dead Sea or the Great
Salt Lake
Eubacteria
 some cause disease
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found in ALL habitats EXCEPT harsh ones
important decomposers for the environment
commercially important in making yogurt, cottage cheese, and buttermilk
Domain Eukarya is divided into Kingdoms
 Protista – Ex: paramecium, slime mold
o Most are unicellular, some multicellular
o Some are autotrophic, while others are heterotrophic
o Aquatic
 Fungi - Ex: mushrooms, yeasts
o Multicellular, except yeast
o Absorptive heterotrophs (digest food outside their body & then
absorb it)
o Cell walls made of chitin
 Plantae (multicellular plants) – Ex: mosses, ferns
o Autotrophic
o Absorb sunlight to make glucose – photosynthesis
o Cell walls made of cellulose
 Animalia (multicellular animals) Ex: fish, reptiles
o Ingestive heterotrophs (consume food & digest it inside their bodies)
o Feed on plants or animals
Taxons
 Most genera contain a number of similar species
 The species homo is an exception (only contains modern humans)
 Classification is based on evolutionary relationships
Cladogram – diagram showing how organisms are related based on shared, derived,
characteristics such as feathers, hair, or scales
Dichotomous Keying
 Used to identify organisms
 Characteristics given in pairs
 Read both characteristics and either go to another set of characteristics
OR identify the organism
Early Taxonomists
 Aristotle was the 1st taxonomist
 He divided organisms into plants and animals
 Further subdivided them by their habitat – land, air, or sea dwellers
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Linnaeus classified organisms by their similar structure
Developed naming system still used today, uses Latin
Called “the Father of Taxonomy”
Developed the modern system of naming known as binomial nomenclature,
genus & species
Standardized Naming System
 Italicized in print
 Capitalize genus, but NOT species
 Underline when writing
Convergent Evolution – different organisms that live in similar environments
become more alike in appearance & behavior Ex: bird wings/insect wings
Coevolution – when 2 species evolve together. There is a mutual evolutionary
influence between 2 species. The species have a symbiotic relationship. Ex: birds &
flowers
Divergent evolution – ancestral species gives rise to a number of new species that
are adapted to different environmental conditions and are less alike. Ex: Darwin’s
finches
Punctuated Equilibrium – some populations don’t change much over time, but have
rapid periods of change in between long stable periods Ex: horseshoe crab haven’t
evolved much but fossil records show short periods of speciation.