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Classification. Ms. Moore 1/14 /12. Why classify?. To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner. Taxonomy : the discipline where scientists classify organisms and assign each organism a universally accepted name.

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Ms. Moore


why classify
Why classify?
  • To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.
  • Taxonomy: the discipline where scientists classify organisms and assign each organism a universally accepted name
early classification systems
Early Classification Systems
  • 350 B.C. Aristole set up 2 kingdoms:
    • Animal
    • Plant
  • 1600s John Ray recognized 2 kingdoms:
    • Animal
    • Plant




Classified by:

Classified by:

Similarities in body structure

common names misleading
Common Names Misleading
  • John Ray noticed that common names were misleading
  • So, he chose to name them in Latin because all scientists knew Latin and it is not spoken so translation is not a problem.
    • Drawback: names were too long!
    • Example: Carnation = dianthus floribussolitoriissquamiscalycinissubovatisbrevissimiscorolliscrenatis
linnaeus to the rescue
Linnaeus to the Rescue!
  • 1700s Carolus Linnaeus developed a two kingdom system
    • Animal
    • Plant
  • Agreed with Ray and used Latin, but gave every organism a two-part scientific name
    • Genus – Species
    • Ex. Homo sapiens
  • This system of classification is known as binomial nomenclature.
binominal nomenclature
Binominal Nomenclature
  • Genus: group of closely related species
  • Species: unique to each species within the genus




linnaeus s system of classification
Linnaeus’s System of Classification
  • Heirarchial system includes 7 levels/taxons:
    • Species
    • Genus
    • Family
    • Order
    • Class
    • Phylum
    • Kingdom
genus species
Genus species
  • Two smallest categories
    • Examples:

Homo sapien

Canis lupus



family order class phylum kingdom
  • Family: groups of genera
    • Ursidae family of bears
  • Order: broad taxonomic category composed of similar features
    • Canidae (dogs) and Felidae (cats)
  • Class: composed of similar orders
    • Mammalia: warm-blooded, have body hair, produce milk
  • Phylum: includes many different organisms that nevertheless share important characteristics
    • Mammals groups with birds, reptiles, etc in the phylum Chordata (backbone)
  • Kingdom: largest and most inclusive of Linnaeus’s taxonomic categories
    • Animals and Plants
  • Species were grouped together in larger taxa according to visible similarities and differences.
  • How would you have classified dolphins?
  • Evolutionary relationships are important in classification.
evolutionary classification
Evolutionary Classification
  • Phylogeny is the study of evolutionary relationships among organisms.
  • Organisms are now grouped into categories that represent lines of evolutionary descent.
  • Grouping organisms together based on their evolutionary history is called evolutionary classification.
  • Species within a genus are more closely related to one another than to species in another genus. This is because all members of a genus share a recent common ancestor.
using cladograms
Using Cladograms
  • Cladograms are diagrams used to show the relationship among organisms with evolutionary innovations—new characteristics that arise as lineages evolve.
  • Characteristics that appear in recent parts of a lineage, but not in its older members are called derived characters.
  • Just like a family tree shows the relationships among different lineages within a family, cladograms represent a type of evolutionary tree.
dna and rna in classification
DNA and RNA in Classification
  • How can DNA and RNA be used in classification?
  • The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships.
  • Humans and yeast related?
    • Myosin
  • The more similar the DNA of two species, the more recently they shared a common ancestor. The more two species have diverged from each other, the less similar their DNA will be.
the tree of life evolves
The Tree of Life Evolves
  • As biologists learn more about he natural world, they realize that Linnaeus's two kingdoms Plantae and Animalia did not represent the full diversity of life.
three domain system
Three-Domain System
  • Eukarya (eukaryote = nucleus)
    • Protista include organisms that cannot be classified as animals, plants, or fungi.
      • Amoeba, Paramecium, slime molds, giant kelp, algae
    • Fungi members are heterotrophs who usually feed on dead or decaying matter.
      • Mushrooms, yeasts
    • Plantae members are photosynthetic autotrophs and immobile.
      • Mosses, fens, flowering plants
    • Animalia includes multicellular and heterotrophic organisms who have no cell wall.
      • Sponges, worms, insects, fishes, mammals
  • Bacteria (prokaryote = no nucleus)
    • Bacteria are unicellular and prokaryotic. Cell walls contain peptidoglycan.
  • Archaea (prokaryote = no nucleus)
    • Archaea are also unicellular and prokaryotic. Cell walls do not contain peptidoglycan.
    • Members of this domain live in some of the most extreme environments you can imagine—volcanic hot springs, brine pools, etc.