Chapter 18
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Why Classify?
◦ Scientists classify organisms into groups in a logical
manner to make it easier to study the diversity of life.
◦ Taxonomy: The discipline of classifying organisms and
assigning each a universally accepted name.
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Assigning Scientific Names
◦ Each species has been assigned a name for classification
purposes.
◦ Binomial Nomenclature: The two part scientific naming
system used in classification.
 The fist name is always capitalized and represents the Genus
of the animal.
 Genus: A group of closely related animals, for example; bears
 The second name is specific to that type of animal.
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Carolus Linnaeus: Developed binomial
nomenclature.
Linnaeus’s hierarchical system of classification
includes seven levels.
The seven layers from smallest to larges are as
follows.
◦ Taxon: A group or level of organization into which
organisms are classified.
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Species  Genus Family  Order  Class
Phylum  Kingdom.
Linnaeus grouped organisms based on physical
similarities and he only had two kingdoms;
Animalia & Plantae.
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Species: A group of similar organisms that
can breed and produce fertile offspring.
Genus: A group of closely related species.
Family: A group of genera that share many
characteristics.
Order: A group of similar families.
Class: A group of similar orders.
Phylum: A group of closely related classes.
Kingdom: Large taxonomic group, consisting
of closely related phyla.
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Dichotomous Key: A key used to identify a
plant or animal in which each stage presents
descriptions of two distinguishing characters,
with a direction to another stage in the key,
until the species is identified.
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Phylogeny: The study of evolutionary
relationships among animals.
Evolutionary Classification: The strategy of
grouping organisms together based on their
evolutionary history.
Biologist group organisms based on evolutionary
descent or phylogeny, not just physical
characteristics.
Derived characters: Characteristics that show up
in recent organism lineage but not in older
organisms.
Cladogram: A diagram that shows evolutionary
relationships.
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There are six (6) kingdoms in modern
classification; Eubacteria, Archaebacteria,
Protista, Fungi, Plantae, and Animalia.
The Three-Domain System:
◦ Modern Biologist have created a new taxonomic
category called domain.
◦ Domain: is a more inclusive category and is larger
than a kingdom.
◦ There are three domains: Eukarya, Bacteria, and
Archaea.
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Eukarya: Eukaryotic, complex, maybe multicellular.
◦ Kingdoms: Protista, Fungi, Plantae, Animalia
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Bacteria: Unicellular, prokaryotic
◦ Kingdom: Eubacteria
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Archaea: Unicellular, prokaryotic, live in
extreme environments.
◦ Kingdom: Archaebacteria
Classification of Living Things
Domain
Bacteria
Archaebacteria
Kingdom
Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
Cell Type
Prokaryotic
Prokaryotic
Eukaryotic
Eukaryotic
Eukaryotic
Eukaryotic
Cell Number
Unicellular
Unicellular
Mostly
Unicellular
Some
Multicellular
Mostly
Multcellular
Some
Unicellular
Multicellular
Multicellular
Mode of
Nutrition
Autotroph &
Heterotroph
Autotroph &
Heterotroph
Autotroph &
Heterotroph
Heterotroph
Autotroph
Heterotroph
Examples
E. Coli
Methanogens
Halophiles
Amoeba
Paramecium
Mold
Mushrooms
Yeast
Mosses
Ferns
Sponges
Mammals
Fish
Streptococcus
Eukarya