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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