Unit 2 The Classification of Living Things

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Unit 2 - The Classification of Living Things
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The Diversity of Life

• Biologists have identified about 1.5 million
  organisms.
• Thousands more remain to be found.
• Great variation in organisms exists.

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Diversity continued

• Some organisms are clearly plant or animal.
• Other organisms are more difficult to classify.
• Thus we need a classification system!

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Plant and Animal Characteristics

• As previously discussed, it is relatively simple
  to distinguish plants from animals.
• See handout.

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Classification Categories

• The categories used by biologists to classify an
  organism are Kingdom, Phylum,Class, Order,
  Family, Genus, and Species.
• See Table 6.1 on page 95.

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Nomenclature

• Nomenclature is a system for naming organisms.
• Linnaeus developed the binomial system of
  nomenclature.

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Nomenclature continued

• Binomial means two names.
• The names must be in Latin.
• The first name is the Genus and the second name
  is the Species.
• For example for a human it is Homo sapiens and
  for the frog Rana pipiens.

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Modern Taxonomy

• In the mid 1800s the common belief was that
  species did not change.
• Biologists collected single specimens that were
  used to represent all species of that one
  organism.
• They called these type specimens.
• Variations were ignored.
• Later in 1859 it was noted that over long periods
  of time a species will change in response to the
  environment.

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Species

• The term species refers to a similar population
  of organisms that can interbreed in nature.
• Over time, species may interbreed, evolve and
  form new species.
• This phenomenon further supports the need for a
  classification system.

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Classification of Living Organisms Handout

• This handout, shows us that we have two broad
  categories of living things
• Prokaryotes and Eukaryotes

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The Prokaryotes

• Cells are called prokaryotic.
• Lack a nucleus.
• Lack membrane bound organelles.
• Ribosomes are smaller than those in eukaryotic
  cells.
• DNA lacks histones (Special protein)
• Flagella are twisted strands of protein.

Ex. Bacteria
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Eukaryotes

• Cells are called eukaryotic
• Cells have a well defined nucleus, with DNA
  containing histones.
• Membrane bound organelles are present(mitochondria
  , etc.)
• Flagella have microtubules in the 92 pattern.

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Three Domain System

• Latest system to classify living things.
• Developed in the last 20 years by microbiologists
  who believe that microbes dominate the diversity
  of life on Earth.
• This system is based on gene studies and in
  particular on rRNA, which is found in all living
  things.

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Three Domain System continued

• The three domains include 2 groups for bacteria
  and 1 for the rest of the living things.
• 1. Archaea Bacteria includes ancient bacteria
  that can be found in very harsh environments.
• Ex. Methane producers, salt lovers,and heat
  lovers.

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Three Domain System continued

• 2. Eubacteria This domain includes the true
  bacteria that are found in various environments
  such as E.coli that is found in the intestines of
  warm blooded animals. Blue - green algae are
  also included in this group.
• 3. Eucharya All remaining organisms. Cells have
  distinct nuclei and organelles.