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TRANSCRIPT
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CLASSIFICATION CLASSIFICATION CLASSIFICATION CLASSIFICATION
CHAPTER 17CHAPTER 17CHAPTER 17CHAPTER 17
Classification & Taxonomy
Classification = grouping organisms based on their characteristics
Taxonomy = the science of naming and classifying organisms
Taxon = a particular category of classification
Why do we classify organisms?• To make things easier to find
– There are A LOT of organisms!
• almost 2,000,000 species discovered!
• To show how things are alike
• To accurately name organisms– People would name newly discovered organisms
anything they wanted• some names as long as 13 words!
• Language barriers
– “Buzzard” in U.S. = vulture
– “Buzzard” in England = hawk
• Easier to determine common ancestry
“Old School” Taxonomy
Aristotle• First to classify
organisms
• Divided organisms into
plants & animals
• Plant groups were
based on size
• Animal groups were
based on where they live:
Land Water Air
Linnaeus’ System of Classification (today’s system)
All living things are categorized into 7 levels:
Kingdom ���� most general category w/ the most indiv.
Phylum
Class
Order
Family
Genus
Species ���� most specific category w/ fewest indiv.
Many different
individuals
Fewest individuals
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Human Taxonomy
Kingdom - Animalia
Phylum - Chordata (backbone)
Class - Mammalia (produce milk)
Order - Primates (2 mammary glands)
Family - Hominoidae (walk on 2 feet)
Genus - Homo (tools, language, culture)
Species - sapiens (small bones, large brain)
Taxa
Taxon
Problems w/ Linnaean Taxonomy
– It doesn’t account for molecular evidence
– It’s based only on physical similarities
• Physical similarities are not always the result of evolutionary relationships
• Molecular similarities more accurately show evolutionary relationships.
Problems w/ Linnaean Taxonomy
• Relies only on physical traits to identify
an organism
• Not always accurate in determining
common ancestry
• Some “organisms” can’t be classified
(i.e. Viruses)
Linnaeus’ Naming System
Living things are named according to the rules of binomial nomenclature:
1. Latin words
2. Written in italics or underlined
3. First name = genus,
second name = species
Puma concolor
• A genus includes one or more physically
similar species.– Species in the same genus are thought to
be closely related.
– Genus name is always capitalized.
• A species descriptor is the second part of
a scientific name.
– often describes the traits
– always lowercase
– always follows genusname; never written alone
Barn owl:
Tyto alba
White oak:
Quercus alba
Why Use Scientific Names?
• Latin is a universal language
• They seldom change…less confusion
• Show relationship of a species
Puma concolor
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Modern Taxonomy Rules
• Evolutionary relationship among organisms: common ancestry
• Chromosome structure
• Reproductive potential
• Biochemical makeup
• Embryological development
Animaliapre-1866
Plantaepre-1866
Protista1866
Archea
Bacteria1977
Fungi1959
Once thought of as plants
Until 1866, only 2 Kingdoms existed:
Monera1938
6 Kingdoms of Life
Kingdom Animalia
• Multicellular, eukaryotic heterotrophs
• Lack cell walls
• Cells organized into
tissues & organs
• Mostly sexual
reproduction
6 Kingdoms of Life
Kingdom Plantae
• Multicellular, eukaryotic
autotrophs (photosynthetic)
• Cell walls made of cellulose
• Some sexual
reproduction, some asexual
6 Kingdoms of Life
Kingdom Fungi
• Mostly multicellular (some unicellular),
eukaryotic heterotrophs (decomposers)
• Cell walls made of chitin
• Some sexual
reproduction,
some asexual
6 Kingdoms of Life
Kingdom Protista
• Most unicelluar
(some multicellular) eukaryotes
• Some heterotrophs, some autotrophs
(photosynthetic)
• Resemble plants, animals and fungi
• Some sexual, some asexual
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6 Kingdoms of Life
Kingdom Bacteria (Eubacteria)• Autotrophic
• Unicellular prokaryotes
• Cells walls made of
peptidoglycan
• Asexual reproduction
• Live almost anywhere,
including humans!
6 Kingdoms of Life
Kingdom Archaebacteria• Chemosynthetic autotrophs
• Unicellular prokaryotes
• Cell walls lack peptidoglycan
• Asexual reproduction
• Live in extreme
environments (salty, hot,
deep in the ocean)
Eubacteria
Prokaryotes are difficult to classify because…
• Some can transfer genetic material to
unrelated species
• New species are
“popping up” all the time!!
Dichotomous Keys
• Use to identify organisms that have
already been classified
• Characteristics given in pairs
• Read both characteristics and either go to
another set of characteristics OR identify
the organism
Dichotomous Keys
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Example of Dichotomous Key
1a Tentacles present – Go to 2
1b Tentacles absent – Go to 3
2a Eight Tentacles – Octopus
2b More/less than 8 tentacles-Go to 3
3a Tentacles hang down – go to 4
3b Tentacles upright–Hydra
4a Balloon-shaped body–Jellyfish
4b Body NOT balloon-shaped - 5
Modern Classification(based on evolutionary relationships)
• Phylogeny = evolutionary history of a
species
• Cladistics = classification based on
common ancestry
– Cladogram = diagram that illustrates
evolutionary relationships
Modern Classification
• Relies on homology (physical similarities)
AND molecular evidence (DNA) to trace common ancestry
DNA analysisDNA analysis
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CladogramDiagram showing how organisms are related
based on shared, derived characteristicssuch as feathers, hair, or scales
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Primate Cladogram
Build a Cladogram