The Tree of Life

Chapter 26

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Why classify organisms?1. Order and organization

2. Common names confusing• Ex. Jellyfish, starfish, etc.

3. Common names vary from place to place• Ex. Cougar, puma, mountain lion

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Aristotle divided organisms into two groups:

Plants Animals1.)herbs 1.)air2.)shrubs 2.)sea3.)trees 3.)land

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Linneaus: founder of modern taxonomy• Classified organisms based on

structural features• Binomial Nomenclature: each species

is given a two-word Latin name1st word = genus

2nd word = species

Ex: canis familiarisfelis domesticus homo sapiens

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The Linnaean Hierarchy Taxa are based on shared characteristics

-Domain (most shared)

-Kingdom

-Phylum

-Class

-Order

-Family

-Genus

-Species (least shared)

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Classification of Organisms

Taxonomy: the science of classifying living things

-A classification level is called a taxon

- taxonomic key: used to identify species, by following a series of choices between characteristics

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Grouping Organisms

3 domains:

-Bacteria

-Archaea

-Eukarya

Archaea and Eukarya are more closely related to each other than to bacteria

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Domain: Bacteriakingdom: Eubacteria

• Unicellular

• Prokaryotic, Cell walls with peptidoglycan

• Some heterotrophic, some autotrophic

• Most abundant organisms on Earth

• Ex: E. coli, Streptococcus, many diseases

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Domain: Archaeakingdom: archaebacteria

• Unicellular

• Prokaryotic, Cell walls lack peptidoglycan

• Most heterotrophic, some autotrophs

• Includes methanogens, extremophiles

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Eukarya

• Eukaryotes appeared about 2.5 BYA

• Key characteristics:– Complex cell organization– Multicellular– Sexual reproduction

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Mitochondria and chloroplasts most likely gained entry by endosymbiosis

-Mitochondria were derived from purple nonsulfur bacteria

-Chloroplasts from cyanobacteria

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Eukaryote Kingdoms

1. Protista• Unicellular (some multi)• Most are heterotrophic• Ex: simple algae, giant kelp,

amoeba, paramecium(Catchall for eukaryotes that

are not plant, fungus or animal)

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2. Fungi• Multicellular (some uni)• Heterotrophic by absorption• Ex: yeast, mold, mushrooms,

athlete’s foot

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3. Plants• Multicellular• Autotrophic• Ex: trees, ferns, tulips,

some algae

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Land plants arose from an ancestral green alga, and only once during evolution

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4. Animals• Multicellular• Heterotrophic by ingestion• Ex: insects, worms, vertebrates

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Molecular systematics is leading to a revision of evolutionary relationships among animals

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Viruses

Are not organisms and so cannot be placed in any of the kingdoms

Are literally “parasitic” chemicals

-DNA or RNA wrapped in protein

Can only reproduce within living cells

Vary greatly in appearance and size