Classification of Organisms
Biology
Chapter 17
Classifying Organisms
• Taxonomy: the science of describing, naming,
and classifying organisms
– Taxon: a group within a taxonomic system
• Aristotle: classified organisms into two groups
– Plants and animals
• Why isn’t this useful?
Carolus Linnaeus
• Devised system of grouping organisms into
hierarchical categories
– Using form and structure
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Domain
Kingdom
Phylum
Class
Order
Family
Genus
species
Binomial Nomenclature
• Two part naming system (scientific name)
– Use genus and species name
– Written in italics with genus name capitalized
– In Latin because it is an unspoken language, so it
never changes
– Example
• Humans: Homo sapiens
Systematics
• Phylogeny: the evolutionary history of a
species
– Phylogenetic Diagram (phylogenetic tree)
• Looks like a family tree and has branching pattern that
indicates how closely related subset taxa are thought to
be
Cladistics
• Cladistics
– A system the uses shared characteristics and
derived characters as the only criteria for grouping
• Shared character: a feature that all members
in the group have in common
• Derived character: a feature that evolved only
within the group under consideration
Cladistics
• Clad: used to describe a group of organisms
that includes an ancestor and all of its
descendants
• Cladogram: Diagram
• Molecular Cladistics: looks at derived amino
acids at each position in a protein
Three Domains of Life
• Domain Bacteria
– Prokaryotic
– Single-celled
– Have a cell wall
– Heterotrophic and autotrophic
– Ex: bacteria
Three Domains of Life
• Domain Archaea
– Prokaryotic
– Most live in harsh environments
– Have cell walls
– Unicellular
– Heterotrophic and autotrophic
Three Domains of Life
• Domain Eukarya
– Have eukaryotic cells
– Includes kingdoms plants, animals, fungi, and
protists
Domain Eukarya
• Kingdom Protista
– Eukaryotic
– Not plants, animals or fungi
– Most are unicellular
– Some multicellular but lack tissue organization
– Autotrophic or heterotrophic
Domain Eukarya
• Kingdom Fungi
– Eukaryotic
– Heterotrophic
– Unicellular and multicellular
– Absorb their food through extracellular digestion
Domain Eukarya
• Kingdom Plantae
– Eukaryotic
– Muclticellular
– Most are autorophic
Domain Eukarya
• Kingdom Animalia
– Eukaryotic
– Multicellular
– Heterotrophic
– Develop from embryos