Classification of Organisms

Chapter 17Modern Biology c2009

1http://en.wikipedia.org/wiki/Pangolin

Classification

• Estimates range from 10 million (to as many as 50 million) species living presently on our planet (only a small fraction of the number that have ever existed in the earth's history) but only around 10% have been classified

• 1,000’s of new species found every year

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Taxonomy• Taxonomy is the biological branch of

classifying or grouping organisms; based on their presumed natural relationship

• a "Taxon" ( taxa - plural) is a category into which related organisms are placed

• Use characteristics of new species compared to similar organisms characteristics

• The way organisms are grouped changes as new information comes in

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So why classify?• organization for study purposes• common names may be misleading (ex:

starfish, jellyfish, prairie dog, groundhog, ringworm, etc)

• scientists need a universal naming system (like metrics)

• shows relationships between organisms (evolutionary path)

• Latin = the universal language of science

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Early Systems of Classification• One of the earliest taxonomic systems was setup by Aristotle around 350 BC, based on his limited observations of organisms.

• In his Scala Naturae ("ladder of life"), he divided creatures up into 2 groups (plants/animals). 

• He further classified animals based on an "either/or" system (blooded -vs- bloodless) and  their means of transportation (air, land, or water). 

• Plants were subdivided based on woody-stemmed or soft-stemmed.

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The Linnaean System• Carolus Linnaeus: (Karl von

Linne)18th century Swedish naturalist; devised system of grouping organisms into hierarchical categories

• Based mostly on form & structure• Originally used 7 levels of

organization:– Kingdom: plant & animals– Phylum (animals); Division (plants)– Class– Order– Family– Genus– species

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TaxonomyCommon Name: Cat, Domestic Shorthair and Longhair

Kingdom: AnimaliaPhylum: ChordataClass: MammaliaOrder: CarnivoraFamily: FelidaeGenus: FelisSpecies: catus

• Today, every living thing has a universal SCIENTIFIC NAME, known as BINOMIAL NOMENCLATURE (2-part name) of Genus & species, which is unique to every living organism.  see examples:

Drosophila melanogaster                     Thamnophis melanogaster

Quercus rubrum               Quercus alba               Acer rubrum

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"Making Order out of Chaos"

SUMMARY:• Species names are Latinized; useful

to scientists around the world• This naming system not only helps to

group things into manageable study categories, it can help to differentiate degree of relationship between organisms. – Phylogeny: evolutionary history of

species or taxonomic group

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Taxon Red Maple White Pine Green Alga

Mountain Lion

Domestic Dog

Grey Wolf Human

KINGDOM Plantae Plantae Protista Animalia Animalia Animalia Animalia

PHYLUM Anthophyta Coniferophyta

Chlorophyta Chordata Chordata Chordata Chordata

CLASS Dicotyledones

Coniferopsida

Chlorophyceae Mammalia Mammalia Mammali

aMammali

a

ORDER Sapindales Coniferales Ulvales Carnivora Carnivora Carnivora Primates

FAMILY Aceraceae Pinaceae Ulvaceae Felidae Canidae Canidae Hominidae

GENUS Acer Pinus Enteromorpha Felis Canis Canis Homo

SPECIES rubrum strobus compressa concolor familiaris lupus sapiens

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The Linnaean System• WITHIN a species, there may also be

BREEDS, RACES, or VARIETIES that show distinctive phenotypes.

• We can also divide the Linnaean categories even further, if needed: subspecies, superclass, subphylum, etc.

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And new things are being discovered all the time!

• Hairy lobster!      ...named Kiwa hirsuto  "The team that found the crustacean said that while legions of new ocean species are discovered each year, it is quite rare to find one that merits a new family.”

• “The family was named Kiwaida, from Kiwa, the goddess of crustaceans in Polynesian mythology. “

(from BBC news story, 2006) What goes into naming a species? (6 minute audio)

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Six-Kingdom System• Although Aristotle classified organisms

as either plants/animals, we now recognize many forms of life are neither.

• Originally 5 kingdoms, but studies showed two important subtypes of bacteria

• Archaebacteria, Eubacteria (Prokaryotic)

• Protista, Fungi, Plantae, Animalia (Eukaryotic)

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Archaebacteria

• Unicellular prokaryotes• Distinct cell membranes, cell walls,

and rRNA• Most species are autotrophic; use

chemosynthesis (methane waste product), but a few are heterotrophic

• “Extremophiles”, live in harsh conditions (ex: hot springs)

• Archae- “ancient”; similar to first chemotrophic prokaryotes on earth13

Eubacteria

• Eu- “true” bacteria• Unicellular prokaryotes• Some species are heterotrophic, others are

autotrophic (photosynthetic or chemosynthetic)

• Responsible for tooth decay, turn milk into yogurt, & food poisoning, important as decomposers

• Most species use oxygen; few cannot live in presence of oxygen

• Eubacteria & Archaebacteria greatest # of living things on Earth

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Eubacteria• Asexual binary fission but can

recombine genes in some ways (conjugation)

• Rapid response to evolutionary change (mutate) because of short generation times

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Protista• A wide variety of eukaryotic,

mostly single-celled organisms– Membrane-bound nucleus & complex

organelles, linear chromosomes• Euglena & amoebas common

unicellular protists• Seaweed, kelp are examples of

species of multicellular protists (but lack specialized tissues, unlike plants)

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Protista• Euglena

– Feed on other organisms– Chloroplasts & photosynthesis– Not a plant

• Amoebas– Feed on other organisms – Respond to touch & light– Not an animal

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Fungi• Heterotrophic, made up of

eukaryotic cells• Absorbs nutrients from decaying

matter• Cell walls made of chitin • Most are Multicellular: mushrooms,

puffballs, rusts, smuts, mildews, mold• A few species are unicellular: Yeasts

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Plantae• Multicellular, eukaryotic• Autotrophic; a few are also

parasitic or carnivorous• Use photosynthesis as source of

energy• Sexual cycle based on meiosis• Mosses, ferns, conifers, and

flowering plants19

Animalia• Eukaryotic cells,

multicellular, heterotrophic • Symmetrical body organization• Move about environment• Standard sexual cycle, meiosis

for recombination of genes

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Three-Domain System• Carl Woese: compared sequences

of ribosomal RNA in different organisms, estimated how long ago pairs of different organisms shared a common ancestor

• All organisms have ribosomal RNA• Domain: one of three broad

groups that all living things fall into on basis of rRNA analysis

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Three-Domain System• Archae

– Kingdom Archaebacteria

• Bacteria– Kingdom

Eubacteria• Eukarya

– Kingdoms Protists, Fungi, Plants, Animals

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Modern Phylogenetic Taxonomy

• Taxonomists today consider morphology (like Linnaeus did), but also use chromosomal characteristics, nucleotide and amino acid sequences, embryological development

• With consideration of all of this evidence and fossil record, yield reliable info about phylogeny of an organism.

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Systematics• Systematics: organizes tremendous

diversity of living things in the context of evolution

• Classification of organism should reflect their phylogeny

• Hypothesis based on several lines of evidence

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Systematics• Phylogenetic tree: family tree that shows

evolutionary relationships thought to exist among groups of organisms

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Systematics• The greater # of homologous

morphological features two organisms share, more closely related they are thought to be.

• Early patterns in embryological development provide evidence of phylogenetic relationships.

• Differences in animal phyla may appear early.

• Blastula: ball of embryonic cells

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Tree of Life

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Systematics• Blastopore an indentation, develops

on outside of blastula• Anterior/Posterior end of digestive

system; Chordates and Echinoderms• Echinoderms: radially symmetrical

marine invertebrate with an endoskeleton; water-vascular system, tube feet (starfish, sea urchin)

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Systematics• Both share important

characteristics like each cell of early embryo is capable of forming entire organism; Twins, Fruit fly parts

• Molecular clock• Chromosome bands

• Chimpanzee/Humans common ancestor– 25 mya to 5 mya using karyotype and

amino acid sequences in proteins 29

Cladistics• Cladistics: system of phylogenetic

classification using shared derived characters to establish evolutionary relationships

• Derived Character: feature that apparently evolved only within the group under consideration– Birds; feathers (only animals to have

feathers)

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Cladistics• Feathers evolved in bird group &

not inherited from distant ancestor of birds

• Shared derived characters, particularly a group of several; evidence of common ancestry between organisms that share them

• Cladogram

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Cladistics• One of most notable nontraditional

conclusion shows crocodiles, birds, and dinosaurs are more closely related to each other than any one of them is to a snake or lizard

• Reptiles did not all spring from one common ancestor

• Composite of several branches that have occurred during evolution of vertebrates

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