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Chapter 18
Classification
Of
Living Things
Finding Order in Diversity
• There are millions of different species on
Earth. To study this great diversity of
organisms, scientists must give each
organism a name & organize them into
groups in meaningful ways.
• Taxonomy is the discipline of naming and
classify organisms.
• Taxonomic names are universally
accepted. Common names for organisms
vary by regions (i.e. cat vs. gato), so a
worldwide acceptance of a single species
name had to occur.
• A good classification system groups
together organisms that are similar to each
other than they are to other organisms.
Carolus Linnaeus
• Scientist in the 1700s who developed
binomial nomenclature.
• Binomial nomenclature is a two-word
naming system that assigns every living
species a two-part name.
• Ex. Ursus maritimus is the species name
for the polar bear. Homo sapiens is the
species name for humans.
• The first part of the name refers to the genus
that a species belongs to and the genus plus
the second part of the name refers to the
species name.
• Ex. All bears belong to the genus Ursus, but only
the polar bear’s species name is
Ursus maritimus.
• Add to notes- First name is always capitalized and
the second name is always lower case; if not
italic the name must be underlined.
• There are 7 different levels (taxons) to Linnaeus’
classification system:
Kingdom
Broadest
Phylum
Class
Order
Family
Genus
Species
Most specific
• Originally, Linnaeus named two kingdoms
(Plantae and Animalia) of all living things,
but later scientists added more.
Modern Evolutionary Classification
• Early classification systems were based
only on visible similarities.
• Biologists now group living things
according to evolutionary relationships.
• Many biologists now use a method called
cladistic analysis, which is based on
derived characteristics. Derived
characters are new traits that arise as a
group evolves over time, so they are found
in closely related species, but not in their
distant ancestors.
• Derived characters can be used to
construct a cladogram, which is a diagram
that shows the evolutionary relationships
among a group of organisms kind of like a
family tree.
Kingdoms and Domains
• As biologists learned more about the
natural world, they learned that Linnaeus’
two kingdoms, Animalia and Plantae, did
NOT accurately represent all living things
on Earth.
• Microorganisms, like bacteria, were
discovered and placed into two kingdoms
called Archeabacteria and Eubacteria.
Protists were seperated and placed into
kingdom Protista and mushrooms, yeaast
and molds were placed into the kingdom
Fungi.
5- Kingdom System of
Classification
• By the 1990s, a six-kingdom system of
classification was proposed. From the most
simple to the most complex they are:
Eubacteria
SIMPLE
Archaebacteria
Protista
Fungi
Plantae
Animalia
COMPLEX
• Recently, scientists have added a new
taxon called the domain, which exists
above the kingdom level of classification.
• The three domains are: Bacteria, Archae
and Eukarya.
• The domain Bacteria contains single-celled,
prokaryotic organisms whose cell walls DO
contain a substance called peptidoglycan.
• The domain Archae contains single-celled,
prokaryotic organisms whose cell walls do NOT
contain the substance peptidoglycan.
• The domain Eukarya contains all organisms that
are Eukaryotic (have nuclei).
»
gram “+” stain appear purple or
brown; thick cell wall
»
gram “-” stain appear pink or
red; thin cell wall or no
wall
Bacteria
Domains
Eukarya
Archae
Archaebacteria
Kingdoms
Eubacteria
Protista, Fungi,
Plantae &
Animalia
Remember the 8 taxonomic levels
of classification
Kingdom
Did King Phillip Cut Onions For Good Soup?
Characteristics
Unicellular, prokaryotic bacteria, whose cell walls contain peptidoglycan; known to
cause disease; fall under Domain Bacteria
Archaebacteria
Protista
Unicellular, prokaryotic bacteria that live in harsh conditions; cell walls DO NOT
contain peptidoglycan; fall under domain Archae
Very diverse group of mostly microscopic, aquatic organisms; in Domain Eukarya
Heterotrophic, eukaryotic organisms that secrete enzymes in order to feed; in
Domain Eukarya
Plantae
Photosynthetic, eukaryotic organisms that are autotrophic; in Domain Eukarya
Very diverse group; all animals are eukaryotic and heterotrophic and exist nearly
every part of the planet; fall under Domain Eukarya
The End
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