The Tree of Life
Chapter 26
Why classify organisms?
1. Order and organization
2. Common names confusing
• Ex. Jellyfish, starfish, etc.
3. Common names vary from place to
place
• Ex. Cougar, puma, mountain lion
2
Aristotle divided organisms into two
groups:
Plants
1.)herbs
2.)shrubs
3.)trees
Animals
1.)air
2.)sea
3.)land
3
Linneaus: founder of modern taxonomy
• Classified organisms based on
structural features
• Binomial Nomenclature: each species
is given a two-word Latin name
1st word = genus
2nd word = species
Ex: canis familiaris
felis domesticus
homo sapiens
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The Linnaean Hierarchy
Taxa are based on shared characteristics
-Domain (most shared)
-Kingdom
-Phylum
-Class
-Order
-Family
-Genus
-Species (least shared)
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Classification of Organisms
Taxonomy: the science of classifying living
things
-A classification level is called a taxon
- taxonomic key: used to identify
species, by following a series of
choices between characteristics
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Grouping Organisms
3 domains:
-Bacteria
-Archaea
-Eukarya
Archaea and Eukarya are more closely related
to each other than to bacteria
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11
Domain: Bacteria
kingdom: Eubacteria
•
•
•
•
Unicellular
Prokaryotic, Cell walls with peptidoglycan
Some heterotrophic, some autotrophic
Most abundant organisms on Earth
• Ex: E. coli, Streptococcus, many
diseases
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Domain: Archaea
kingdom: archaebacteria
•
•
•
•
Unicellular
Prokaryotic, Cell walls lack peptidoglycan
Most heterotrophic, some autotrophs
Includes methanogens, extremophiles
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Eukarya
• Eukaryotes appeared about 2.5 BYA
• Key characteristics:
– Complex cell organization
– Multicellular
– Sexual reproduction
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Mitochondria and
chloroplasts most
likely gained entry
by endosymbiosis
-Mitochondria were
derived from purple
nonsulfur bacteria
-Chloroplasts from
cyanobacteria
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Eukaryote Kingdoms
1. Protista
• Unicellular (some multi)
• Most are heterotrophic
• Ex: simple algae, giant kelp,
amoeba, paramecium
(Catchall for eukaryotes that
are not plant, fungus or
animal)
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2. Fungi
• Multicellular (some uni)
• Heterotrophic by absorption
• Ex: yeast, mold, mushrooms,
athlete’s foot
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3. Plants
• Multicellular
• Autotrophic
• Ex: trees, ferns, tulips,
some algae
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Land plants arose from an ancestral green
alga, and only once during evolution
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4. Animals
• Multicellular
• Heterotrophic by ingestion
• Ex: insects, worms, vertebrates
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Molecular systematics is leading to a revision
of evolutionary relationships among animals
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Viruses
Are not organisms and so cannot
be placed in any of the kingdoms
Are literally “parasitic” chemicals
-DNA or RNA wrapped in protein
Can only reproduce
within living cells
Vary greatly in
appearance and size
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