Chapter 18
Classification

Taxonomy - the science
of classifying organisms
and giving them a
universally accepted
name.
Aristotle (384 - 322BC)
Aristotle’s Groups
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He divided all living things into 2 major
groups
1. Plants
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classified by size and structure
2. Animals
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classified by habitat (where they lived)
HISTORY: Aristotle
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Problems with his system:
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Frogs live in both water and on land
HISTORY: Aristotle
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Problems with his system:
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Bats, birds and flying insects were
grouped together
HISTORY:
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Carolus Linnaeusdeveloped the
modern system of
classification
Father of Taxonomy
Carolus Linnaeus (1707-1778)
MODERN CLASSIFICATION SYSTEM
 Organisms are grouped together on
the basis of:

Similarity in structure
Panthera leo
Felis rufus
Felis domesticus
Similarity in structure
Canis lupus
Similarity in structure
Canis latrans
Similarity in structure
Canis domesticus
Organisms are grouped together on the
basis of:

Similarity of embryonic development
Organisms are grouped together on the
basis of:

Similarity in evolutionary history
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Phylogeny: the evolutionary history
of a species based on comparing
relationships between species using the
fossil record
Organisms are grouped together on the
basis of:

Similarity in behavior
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Classification is based on close
evolutionary relationships of
organisms.
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Organisms classified in the same taxa
(pl.) (taxon, sing.) share a common
ancestry. They have evolved from the
same common ancestral organism.
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Binomial nomenclature - classification
system developed by Carolus Linnaeus
that assigns each organism a two-part
name.
-Scientific name is ALWAYS in italics.
-Scientific name is ALWAYS in Latin.
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-First word- CAPITALIZED, second
word- lowercase
The first word is the genus in which the
animal belongs to and the second word is
the species in which the animal belongs
to.
-Example- Homo sapiens (Humans)
Binomial Nomenclature
Scientific Name:
Rudbeckia hirta
Common Name:
Gloriosa daisy
or Black-eyed Susan
Binomial Nomenclature
Scientific Name:
Pinus virginianis
Common Name:
Virginia Pine
Binomial Nomenclature
Scientific Name:
Harmonia axyridis
Common Name:
Asian Ladybug
Binomial Nomenclature
Scientific Name:
Ophiophagus
hannah
Common Name:
King Cobra
Species

Organisms that belong to the same
species can mate AND produce FERTILE
offspring.

Horses and donkeys can mate.

They produce a mule.
 Mules
+
are INFERTILE
=

Lions and tigers can mate.

They produce a liger.
 Ligers
+
are INFERTILE
=
Why use scientific names?

Common names do not indicate how
organisms are related or classified.

Common names can be misleading.
(e.g., seahorse, weeping willow)

Organisms with more than one
common name leads to mass
confusion.
Why Latin?
 Latin is no longer spoken, and
therefore, does not change as spoken
languages do.
 So, scientific names remain the same
forever.
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Linnaeus's System of Classification
-hierarchical
Kingdom
Phylum
Class
Order
Family
Genus
Species
-Each of these levels is called a taxon (taxa)
Kingdom
Phylum
Class
Order
Family
Genus
Species
K__________ p__________ c_________
o___________ f________ g_________
s________.
Kings play chess on fine gold sets.
K__________ p__________ c_________
o___________ f________ g_________
s________.
King Phillip came over for great soup.
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-The kingdom is the largest of Linnaeus's
taxonomic categories.
(Linnaeus named two kingdomsAnimalia and Plantae)
-His system was based on visible
similarities and differences
Can you think of any problems with this?

All organisms, living or extinct, are
descendants of the first cells. Because
they all share a common ancestor, all
organisms are related to one another, no
matter how different they seem.

Relationships among taxa can be
illustrated on a family, or phylogenetic
tree.
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-The tips of the branches represent the
most modern organisms to evolve.
-The base represents common ancestors
from which the organisms at the tip
evolved.
-Each time a branch divides, it show the
emergence of a new ancestral species.
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Cladistic analysis - scientific search for
ancestral relationships among species.
Cladogram - phylogenetic trees
constructed from a two-way branch
points that show the evolutionary
relationships among a group of
organisms.
Derived characters - homologous
characteristics that unite the organisms in
a group.
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When a scientist is in the field and finds
an organism they do not recognize,
he/she uses a dichotomous key to
identify it.
This key is a list of observable traits that
eventually lead you to the name of the
organism.
The observations are presented as choices.
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Kingdoms and Domains
Six kingdom system of classification:
-Bacteria (Eubacteria)
-Archaebacteria
-Protist
-Fungi
-Plant
-Animal
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Domain Bacteria
-polymerases are small and simple
-cell walls contain peptidoglycan
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Domain Archaea
comes from a Greek work meaning
"ancient"
live in extreme environments
polymerases are complex and similar to
eukaryotes
cell wall does not contain peptidoglycan
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Domain Eukarya
all organisms have a nucleus (eukaryotes)
Protist, Fungi, Plant, and Animal.