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Name
Date
XBIO: Classification of Organisms NOTES
Biodiversity - the variety of organisms on the planet
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Over 2 million species have been named and
classified
Throughout history different classification
systems have been used to categorize organisms
Classification systems place species into
categories based on particular characteristics
Taxonomy - the science of describing, naming, and
classifying organisms
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Taxon – a group within a taxonomic system (taxa
= plural)
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Aristotle – 2,400 years ago classified organisms
into 2 taxa:
1. Plants (further grouped on differences
in their stems)
2. Animals (then by whether they lived on
land, in water, or in air)
3. As more organisms were classified this
system became inadequate
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Carolus Linnaeus – grouped organisms into
hierarchical categories based on their form and
structure
 Each category represents a level of
grouping from larger, more general
categories to smaller, more specific
categories
Period
Levels of Classification
BROAD
(larger, more general)
SPECIFIC
(smaller, more specific)
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Binomial nomenclature – “two name naming system” created by Linnaeus
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Organisms named using Genus species or Genus species
Genus is capitalized, species is lowercase
Written in italics or underlined
Also called the scientific name
Examples
o Homo sapiens - Humans
o Canis lupus – Grey wolf
o Felis leo – Lion
o Felis catus – Domestic cat
o Ursus arctos – Brown bear
o Pinus strobus – Eastern white pine
Different Ways to Classify Organisms
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Phylogenetics – the analysis of evolutionary or ancestral relationships among
taxa usually leads to the creation of a phylogenic diagram/tree using:
o
fossils
o
homologous features
o
embryolical evidence
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Cladistics – a system of phylogenetic analysis that uses shared and derived
characters as the ONLY criteria for grouping taxa
o
Shared character – a
feature that all members
of a group have in
common (ex: hair in
mammals, feathers in
birds)
o
Derived character – a
feature that evolved only
within the gropu under
consideration (ex:
feathers in birds)
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Clade – group of organisms that includes an ancestor plus all of its descendants
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Cladogram – phylogenetic tree based on cladistics
Constructing a Cladogram
1.
2.
3.
4.
5.
6.
Make a data table
Chose an out-group (a group that is only distantly related to the other organisms)
Score the characteristics (yes vs. no, 1 vs. 0)
Observe the character that is shared by all organisms = first branch
Continue with the next most commonly shared character = next branch
Continue until all characters are used
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Can be constructed using:
o
Shared/derived characters
o
Molecules (DNA, RNA, amino acids, proteins)
o
Chromosomes
Classification is an on going process
 Will be revised as new information and organisms are discovered
 Will be revised as new technology is created
Modern Classification System
3 Domains – 6 Kingdoms
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Domain Bacteria
o Kingdom Eubacteria
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Domain Archaea
o Kingdom Archaebacteria
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Domain Eukarya
o Kingdom
o Kingdom
o Kingdom
o Kingdom
Protista
Fungi
Plantae
Animalia