Chapter 15: Biological Classification

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Chapter 15 Biological Classification
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What is this?
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These are some of the common names for this
animal. Scientists have assigned it a single
scientific name Porcellio scaber
Sow bug
Wood louse
Potato bug
Pill bug
Roly-poly
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The Importance of Scientific Names

• Each kind of organism on Earth is assigned a
  unique two-word scientific name
• Binomial nomenclature
• All biologists, regardless of their native
  language, use scientific names when speaking or
  writing about organisms
• Most organisms also have common names
• Using scientific names enables scientists to
  exchange information about an organism and to be
  certain that they are referring to the same
  living thing

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Whats in a Scientific Name?

• First word describes the organism in a general
  way
• The second word identifies the exact kind of
  living thing
• The first word of a scientific name is the name
  of the genus to which the organism belongs
• Group of animals that share major characteristics
• The second word in a scientific name identifies
  one particular kind of organism within the genus
• Scientists call each different kind of organism a
  species
• The correct name for an organism must include
  BOTH parts of its scientific name

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Comparison of Red Oak and Willow Oak
Red Oak Willow Oak
Genus Name Quercus Quercus
Scientific Name Quercus rubra Quercus phellos
Traits Acorns about 25mm long Common in open Northeastern forests tolerant of city soot and cold temperatures Lobed leaves Acorns about 15mm long Popular shade tree found in the South grows well in rich, moist soil Unlobed, narrow leaves
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Scientific Names Must Conform to a Set of Rules

• All scientific names must consist of Latin words
• Two different organisms cannot be assigned the
  same name
• Organisms in different genera cannot have the
  same genus name
• When choosing a name for a species, biologists
  often pick a name that describes the appearance
  or distribution of an organism

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The second word of a scientific name is often
descriptive of an organism or its distribution.
The green anole lizard Anolis carolinensis and
the chickadee Parus carolinensis are both found
in North Carolina and South Carolina.
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Tyrannosaurus rex, which means tyrant-lizard-king
, was named for its enormous teeth and
tremendous size. This dinosaur measured about 50
feet in length.
The frog Rhinoderma darwinii was named to honor
Charles Darwin.
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Why are Scientific Names in Latin?

• In the Middle Ages, when scientists began to name
  organism, Latin was used in academic circles
• Scientists and other scholars found it easier to
  communicate with each other in Latin
• Latin was the language of the scholar and was
  used for all spoken and written communication
• Easier to still use Latin than to rename all 1.4
  million known organisms
• Latin is a universal language

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Linnaeus Devised the Two-Name System

• The modern system of naming organisms was
  developed by Swedish botanist Carl Linnaeus
• In Linnaeuss day, organisms were given very long
  Latin names (sometimes more than 15 words), which
  were often changed according to the whims of
  particular scientists
• Linnaeus assigned a standard, two-word Latin name
  to each organism known in his time

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Writing a Scientific Name is Simple

• When you write a scientific name, always
  capitalize the genus name
• Begin the second word with a lowercase letter
• Both parts of a scientific name are underlined or
  written in italics
• Homo sapiens
• Homo sapiens
• After the first use of the full scientific name,
  the genus name can be abbreviated as a single
  letter if the meaning is clear
• H. sapiens

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Classification of Living Things

• The Greek philosopher Aristotle grouped animals
  by their physical similarities
• Today biologists classify organisms based on
  their physical, genetic, biochemical, and
  behavioral similarities
• The classification of organisms is based on
  decisions made by many scientists using available
  information

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Classification of Living Things

• The science of classifying living things is
  called taxonomy
• Taxonomists are scientists who examine, classify,
  and argue about where organisms fit in a group
• In a hierarchal system of classification, species
  are assigned to genera, genera are assigned to
  families, and families are assigned to groups of
  increasing size

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Organisms are Classified by Similarity

• In biological classification, organisms are
  assigned to a group because they share
  distinctive characteristics with other members of
  that group
• The biological hierarchy of classification has
  seven different levels
• Kingdom, phylum, class, order, family, genus, and
  species

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Organisms are Classified by Similarity

• The smallest group in biological classification
  is the species
• Similar species are collected into a genus
• Similar genera are united into a family
• Families that are alike are combined into an
  order
• Similar orders are collected into a class
• Classes are united into a phylum
• Finally, similar phyla are collected into a
  kingdom
• The more classification categories two species
  share, the more traits they have in common

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Kingdom
Phylum
Class
Order
Family
Genus
Species
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Biological Classification

• Kristy
• Poured
• Coffee
• On
• Freds
• Green
• Shirt

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

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Classification and Evolution

• The biological hierarchy of classification is
  based on the fact that different degrees of
  similarity exist among organisms
• For Darwin, classification provided strong
  evidence supporting evolution
• Organisms are similar because they descended from
  a common ancestor
• The more similarities two organisms share, the
  more recently they shared a common ancestor
• Thus, the more classification categories two
  organisms share, the more closely related they are

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Similarity Does not Guarantee Close Relationship

• Compare the two ocean-dwelling animals seen here
• Both have stream-lined bodies, paddle-like fins,
  and flattened tails
• Would you say these organisms are closely related?

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gills obtain oxygen from water belongs to the
class Chondrichthyes skin has placoid
(toothlike) scales skeleton of
cartilage vertical tail fin
breathes air through lungs belongs to the class
Mammalia skin has hair skeleton of
bone horizontal tail fin
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Similarity Does not Guarantee Close Relationship

• Similar appearance does not guarantee common
  ancestry
• Because the number of differences between sharks
  and dolphins far exceeds the number of
  similarities, it is easy to reject the hypothesis
  that these animals are close relatives

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Methods of Taxonomy

• The example of the shark and dolphin illustrates
  the difficulty in determining which similarities
  will be useful when classifying an organism
• There are two alternative methods of choosing
  which similarities are important
• The first method is cladistics

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Taxonomy and Technology

• Biologists have traditionally compared the
  appearances of organisms in order to discover the
  relationships among them
• Biologists also consider the behavioral patterns,
  methods of reproduction, life cycles, and
  development from fertilization to adulthood
• Technological advances have enabled biologists to
  study the genes that produce the traits used to
  classify organisms

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Taxonomy and Technology

• Taxonomists use techniques of molecular biology
  to compare the DNA nucleotide sequences of
  different organisms
• Comparisons of DNA sequences are especially
  important for the taxonomist because mutations
  are random events
• As time passes, more mutations tend to occur in
  the DNA of a particular species
• Thus, DNA acts as a molecular clock

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What Is a Species?

• A species is just a level in the classification
  system to which scientists assign very similar
  organisms
• Over time, species change and give rise to new
  species in a process known as speciation
• Biologists have traditionally defined a species
  as organisms that are able to interbreed with
  each other to produce fertile offspring and that
  usually do not reproduce with members of other
  groups

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What Is a Species?

• This definition works well for most animals
• For example, the horse and the zebra belong to
  different species
• Although they can mate, the resulting offspring,
  the zebroid, is sterile
• Reproductive barriers between species are not
  always perfect
• Hybrids are offspring that result from
  interbreeding by individuals of different species
• Coyotes, dogs, and wolves

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A Species is a Unique Kind of Organism

• A species is basically a unique kind of organism
• Members of a species share at least one inherited
  characteristic not found in other similar
  organisms
• In sexually reproducing species, this distinctive
  characteristic is maintained from generation to
  generation because members of different species
  do not interbreed

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Six Kingdom System

• Biologists used to classify every living thing
  into either kingdom Plantae or kingdom Animalia
• However, numerous living things do not quite fit
  either description
• For example, where would a mushroom fit?
• Since Linnaeuss time, biologists have learned a
  great deal about the structure and function of
  living things

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Six Kingdom System

• This information has enabled them to make
  increasingly precise distinctions among the major
  groups of organisms
• Most biologists now use a six-kingdom system of
  classification
• Archaebacteria
• Eubacteria
• Protista
• Fungi
• Plantae
• Animalia

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Bacteria

• All prokaryotes, also called bacteria, are in the
  kingdoms Archaebacteria or Eubacteria
• The bacteria represent the most ancient groups on
  earth
• They have adapted to almost every environment
• All bacteria lack cell nuclei

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Kingdom Archaebacteria

• The archaebacteria evolved before oxygen filled
  our atmosphere and now are found in extreme
  environments
• Fewer than 100 species have been recognized so
  far
• Archaebacteria are believed to be the ancestors
  of the protists

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Kingdom Eubacteria

• Contains most of the common bacteria that share
  our world
• They are an extremely diverse group, containing
  both autotrophic and heterotrophic forms
• Approximately 5,000 species have been
  characterized so far, but many more exist
• Eubacteria are believed to be the ancestors of
  mitochondria and chloroplasts, organelles within
  eukaryotic cells

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Kingdom Protista

• All the multicellular eukaryotes not classified
  as plants, animals, or fungi are assigned to this
  kingdom
• Protists include protozoa, such as Amoeba and
  Paramecium, and algae, such as seaweeds and kelps
• Slime molds and water molds also belong to this
  kingdom

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Kingdom Fungi

• Mushrooms, yeast, and molds are members of this
  kingdom
• Instead of roots, stems, and leaves, fungi are
  made of thin filaments that penetrate the soil or
  decaying organisms, absorbing nutrients from them
• Fungi do not contain chloroplasts and cannot make
  their own food by photosynthesis

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Kingdom Plantae

• This kingdom includes only terrestrial
  multicellular organisms that use photosynthesis
  to obtain their nutrients
• Nearly all plants occur on dry land, but a few
  grow submerged in fresh water, and a very few
  grow at the edges of the sea
• Plants cells have cell walls
• Because some green algae are so similar to plants
  they have been identified as the ancestral groups
  for this kingdom

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Kingdom Animalia

• The first members of this kingdom evolved in the
  ocean
• The largest number of animal phyla are still
  found only in the sea
• Organisms in kingdom Animalia are multicellular
• Animals do not photosynthesize
• Their cells do not have cell walls
• Nearly all animals have some sort of nervous
  system

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