ClassificationChapter 17, Sections 1 and 4
Why classify?Provides a way to
organize living things
Ensures scientists are using a common language when talking about living things
How are Things Classified?Old way – by physical similaritiesNew way – by molecular (DNA,
RNA, amino acid) similarities Increased understanding about
DNA has caused some revisions
Who & When: Development of Today’s Classification
SystemCarolus
Linnaeus - a Swedish botanist
During mid-1700s
Only 2 kingdoms – plants and animals
Levels of ClassificationFrom broadest
(biggest) group to most specific (smallest): Kingdom Phylum Class Order Family Genus Species
There are many mnemonic devices to help you remember these levels; write down your favorite or make up a new one:
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Rules for Scientific NamingEach species’ name is unique and
usually descriptiveScientific names:
Latin or Latinized wordsGenus and species name
This is called binomial nomenclature (two-name naming)
Genus name is capitalizedSpecies name is all lowercaseBoth words are italicized or
underlined
Two KingdomsUp until the 1950s – 1960s, most
textbooks still only referred to two kingdoms:Plants, which included all bacteria
and fungiAnimals, which included all protozoa
(single-celled, eukaryotic organisms)
Five Kingdoms In 1959, Whittaker developed the
5-Kingdom system
Monera included all of the prokaryotes (cells without nuclei); all others were eukaryotic.
Six KingdomsMore recently,
scientists split the kingdom Monera into two distinct groups (Eubacteria & Archaebacteria), creating 6 Kingdoms
Kingdoms of Life, cont’dThese six
kingdoms have now been grouped under a higher category: domain
There are 3 domains:BacteriaArchaeaEukarya
Characteristic Archae-bacteria Bacteria Protista Fungi Plantae Animalia
Cell Type (prokaryotic or
eukaryotic)Prokaryotic Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
# of cells (uni or multicellular) Unicellular Unicellular Unicellular &
MulticellularUnicellular & Multicellular Multicellular Multicellular
Presence or absence of
nucleus in cellAbsent Absent Present Present Present Present
Presence or absence of cell
wallPresent Present Present in
some Present Present Absent
Cell wall composition
No peptidoglycan Peptidoglycan Varies Chitin cellulose n/a
Mode of nutrition (hetero /
autotrophic)
Autotrophic & heterotrophic
Autotrophic & heterotrophic
Autotrophic & heterotrophic Heterotrophic Autotrophic Heterotrophic
Presence or absence of locomotion
Present in some
Present in some
Present in some Absent Absent Present
Characteristics of Each Kingdom
Dichotomous KeysDichotomous keys are used to
distinguish between organisms that are closely related.
At each step on the key, the user is given two choices. Each alternative leads to another question, until the organism is identified.
Sample Dichotomous Key
Sample Dichotomous Key
This simple example of a dichotomous key shows
how each “question” must be a yes / no
question that divides the organisms into two
groups.