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Chapter 20 Classification of Living Things


Chapter 20 Classification of Living Things Taxonomy Science of Classification Branch of biology concerned with identifying, describing and naming organisms. – PowerPoint PPT presentation

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Title: Chapter 20 Classification of Living Things

Chapter 20 Classification of Living Things
Taxonomy Science of Classification
  • Branch of biology concerned with identifying,
    describing and naming organisms.
  • Ideally, classification is based on our
    understanding of how organisms are related to one
    another through evolution
  • Not an artificial system

Taxonomy - History
  • Began with Greeks and Romans
  • Aristotle - first taxonomic system
  • Plants trees, shrubs, and herbs
  • Animals air-dwellers, water-dwellers,
  • System flawed because scientifically valid
    characteristics were often not used in
    determining the categories.

Carolus Linnaeus (Sweedish botanist) father of
modern taxonomy (1707- 1778)
  • Eliminated use of common names
  • Used Latin as a basis for nomenclature
  • Created "binomial nomenclature" identifying each
    organism by a two-part name

Linneaus, contd
  • Used morphological (form structure)
    characteristics as a basis for classification
  • Linnaeus considered each species to have a unique
    structure that made it distinct

Species name Scientific name
  • e.g. Magnolia grandiflora underlined
  • Magnolia grandiflora italicized
  • genus - Magnolia
  • specific epithet - grandiflora
  • species - Magnolia grandiflora M. grandiflora

  • Created seven taxa for classification purposes
  • Kingdom..most inclusive
  • Phylum
  • Class
  • Order
    Classification Family
  • Genus
  • Species.least inclusive
  • Taxon a group of organisms that fills a
    particular category of classification

Hierarchy of taxa for Callinectes sapidus
Callinectes (Gk. Beautiful swimmer) sapidus (L.
  • Domain Eukarya (Eucaryota)
  • Kingdom Animalia
  • Phylum Arthropoda
  • Class Malacostraca
  • Order Decapoda Atlantic Blue Crab
  • Family Portunidae
  • Genus Callinectes
  • Species Callinectes sapidus

Classification of organisms
  • Additional levels of classification can be added
    by adding super-, sub-, or infra- (e.g.,
  • Taxonomists lumpers or splitters

Classification of organisms
  • the higher the classification category, the more
    inclusive it is
  • A character is any structural, chromosomal, or
    molecular feature that distinguishes one group
    from another.
  • members of a kingdom share general characters
    members of a species share quite specific

  • The Linnaean system of classification is still
    in use today.
  • Linnaeus was devoutly religious, but his
    taxonomic system was later to be used to
    demonstrate the phylogenetic (evolutionary)
    relationships among living organisms.
  • Linnaeus Latinized his own name from
  • Carl von Linne

Some points about species
  • The biological definition of a species states a
    group of organisms capable of interbreeding and
    producing fertile offspring they share the same
    gene pool.
  • Distinguishing species on the basis of
    reproductive isolation can also be a problem.
  • Some species do not reproduce sexually.
  • Some species hybridize where their geographic
    ranges overlap.
  • Reproductive isolation can be difficult to
  • When a species has a wide geographic range,
    variant types may tend to interbreed where they
    overlap these populations are called subspecies,
    and are designated by a three-part name.

Genus name may include more than one species or
Ursus americanus
Ursus maritimus
Ursus thibetanus
binomial and trinomial
Ursus arctos mittendorfii
Ursus arctos horribilis
Classification - an ongoing process
  • there are estimated to be between 3 and 30
    million species living on earth
  • we have currently named one million species of
    animals and a half million plant and
    microorganismic species
  • some groups, such as birds, are nearly all known
    some insect groups are mostly unknown 

Major kingdoms of life
  • Work of R.H. Whittaker (1969)
  • Five are generally recognized based on
  • Cell type
  • Organization
  • Nutrition

Five Kingdoms of Life (KEY)
  • 1. Cell type
  • A. Prokaryotic (P) - primitive, lack
    membrane-bound internal organelles
  • B. Eukaryotic (E) - true nucleus, membrane-bound
  • 2. Cells
  • Unicellular (U)
  • Colonial (C)
  • Multicellular (M)
  • 3. Nutrition
  • A. Autotrophic (A) - Source of carbon is simple,
    such as carbon dioxide (CO2)
  • B. Heterotrophic (H) - Source of carbon is
    complex, such as
  • carbohydrates, proteins, lipids, or
    nucleic acids

(1) Monera Bacteria P U H
Blue-green algae P U, C A
(2) Protista Protozoa E U H
Algae E U,C A
Seaweeds E M A
(3) Fungi Mushrooms E M H
Yeasts E U H
(4) Plantae Mosses, Liverworts, Ferns, Gymnosperms, Angiosperms E M A
(5) Animalia Sponges, Cnidaria, Worms, Arthropods, Molluscs, Echinoderms, Chordates E M H
Kingdoms of Life
  • Many modern taxonomic systems split bacteria
    (Monera) into several different kingdoms.
  • Generally,
  • protists are considered to have evolved from
    monerans, and
  • the fungi, plants, and animals evolved from
    protists via three separate lineages.

A higher category, the domain, has been proposed
to be added to these 7 categories
  • Three-Domain System
  • sequencing of rRNA suggests all organisms evolved
    along three distinct lineages domains
  • Bacteria
  • Archaea
  • Eukarya

Three Domains
  • 1. the bacteria diverged first archaea and
    eukarya are more closely related than either is
    to bacteria
  •       2. the archaea live in extreme
    environments methanogens in anaerobic swamps,
    halophiles in salt lakes, and thermoacidophiles
    in hot acidic environments
  •      the archaea cell wall is diverse but
    not the same as the bacterial cell wall
  •       3. the eukarya contains unicellular to
    multicellular organisms, always with a
    membrane-bound nucleus 

Phylogenetic (Evolutionary) Trees
  • Systematics is the study of the diversity of
    organisms using information from cellular to
    population levels
  • (Cell, tissue, organ, organism, population)
  • A goal of systematics is to determine phylogeny
  • Phylogeny is the evolutionary history of a group
    of organisms
  • Evolution is a core theme of biology.
  • Evolution - the process by which life on earth
    has changed over time.

Phylogenetic (Evolutionary) Trees
  • a phylogenetic tree indicates common ancestors
    and lines of descent or lineages
  • an ancestral (primitive) character is a trait
    that is present in a common ancestor and all
    species in its lines of descent
  • a derived character is present only in a
    specific line of descent
  • Different lineages diverging from a common
    ancestor have ancestral characteristicstraits
    shared by the ancestor and the species in its
    lines of descent.

Simple phylogenetic tree
(skeletal differences)
(tree climbing)
All give birth to live young
(placental mammal)
highly branched
hollow horns male/female
solid horns (antlers) male only
even-toed hoofs
Classification and Phylogeny
Tracing Phylogeny
  • Systematists use various methods used to discover
    evolutionary relationships between species.
  • If you can determine common ancestors, then you
    know how evolution occurred and you can classify
    organisms correctly.

Fossil Record
  •       because fossils can be dated, fossils can
    establish the age of a species
  •       most organisms decay and the chances of
    becoming a fossil are low

Homology morphological data
  •       Homology is a character similarity that is
    due to having a common ancestor (anatomical and
    embryological features)
  •       homologous structures are related to each
    other through common descent but may differ in
    structure and function (e.g., the forelimbs of a
    horse and the wings of a bat)
  •       analogous structures have the same
    function but are not derived from the same organ
    in a common ancestor (e.g., the wings of an
    insect and the wings of a bat)
  •       convergent evolution is acquisition of
    similar traits in distantly related lines of
    descent as a result of adaptation to similar
    environmental conditions
  •   --both spurges and cacti are adapted to a
    hot, dry environment and are both similar, but
    details of flower structure indicate these two
    groups are not closely related
  •       parallel evolution produces similar
    characters in related lineages without occurring
    in a common ancestor

Molecular Data
  •       Speciation (new species) occurs when
    mutations bring about changes in base pair
    sequences of DNA
  •       Protein Comparisons
  •        earlier studies used immunological
    reactions to antibodies, made by injecting a
    rabbit with cells of one species, to determine
    the relatedness of two species
  •        we now use amino acid sequences to
    determine the differences in proteins between two
  •        cytochrome c is a protein found in all
    aerobic organisms the amino acid differences in
    cytochrome c between chickens and humans is 13
    but between chickens and ducks is only 3
  •        since the number of universal proteins is
    limited, most new studies use differences in RNA
    and DNA.

RNA and DNA Comparisons
  •       all cells have ribosomes for protein
    synthesis comparing rRNA base pair sequences
    provides a reliable indicator of similarity
    between organisms
  •       Chimpanzees and Humans
  •        DNA DNA hybridization shows chimpanzees
    closer to humans than to other apes
  •        yet humans are kept in a separate family
    and chimpanzees are with the ape family due to
    differences in adaptation to the environment
  •       Mitochondria DNA (mtDNA) changes ten times
    faster than nuclear DNA
  •        mtDNA is often used for closely related

Phenogram DNA data
  • Length of branches
  • indicates the relative
  • number of nucleotide
  • pair differences among
  • species shown.

Molecular Clocks
  •       When nucleic acid changes are not tied to
    adaptation - the fairly constant changes provide
    a "molecular clock to indicate relatedness and
    evolutionary time
  •       the fossil record can then be used to
    calibrate the clock and confirm the hypothesis
    drawn from molecular data

Systematics today 3 main schools
  • 1. Cladistic Systematics (Willi Hennig)
  •       cladistics analyzes primitive and derived
    characters and constructs cladograms on the basis
    of shared derived characters (homologies)
  •       cladogram a diagram showing relationships
    among species based on shared, derived characters
  •       a clade is an evolutionary branch - that
    includes a common ancestor and all its descendent
    species (monophyletic taxon)
  • outgroup - taxon (taxa) that define the
    primitive characters of the study group study
    group taxa placed in a clade
  •       Parsimony
  •        cladists are guided by principle of
    parsimony the minimum number of assumptions is
    most logical that is, the fewest number of
    shared derived character are left unexplained

Charcters of taxa being compared
Cladogram w/ 3 clades
monophyletic taxon
Common ancestor notochord in embryo
Notochord- shared ancestral character Others are
shared derived characters
Systematics today
  • 2. Phenetic Systematics
  •       phenetic systematists cluster species on
    the basis of the number of shared similarities,
    regardless of whether they might be convergent,
    parallel, or depend on one another
  •       results of their analysis are depicted in a
  •       phenograms vary for the same group of
    organisms, depending on how the data are
    collected and handled

Systematics today
  • 3. Traditional Systematics
  •       traditional systematics stresses common
    ancestry and the degree of structural
    (anatomical) difference among divergent groups in
    order to construct phylogenetic trees
  •        a monophyletic group does not include all
    groups from all ancestors (as a clade does)
  •       cladists would not use "reptiles" because
    it does not include all organisms derived from

Traditional vs. cladistic systematics
Hair/ mammary glands
scaly skin
Traditional view
Cladistic view
Common ancestor-egg layer