1 Classification of Life. 2 Why Classify Organisms? To aid them in their study of the large...
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Classification of Life
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Why Classify Organisms?
• To aid them in their study of the large diversity of organisms, biologists classify organisms by naming them and by grouping them in a logical manner.
• Taxonomy is the discipline scientists use to classify and name organisms.
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Binomial Nomenclature
• From the time of Aristotle until the 1700s, all living things were classified into two kingdoms, the plant and animal kingdom.
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• In the 1700s, Carolus Linnaeus, a Swedish botanist, developed a classification system based on
Carolus Linnaeus1707 - 1778
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anatomical similarities and differences.
• Linnaeus developed binomial nomenclature, a two-word naming system.
• The first word is the genus. The genus is always capitalized.
• The second word is the species. The species is written in lowercase.
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• Both the genus and the species are italicized. For example
Homo sapiens (human)
Felix domestica (house cat)
Panthera leo (lion)
Ajuga reptans (ajuga)
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• A taxon is a group or level of organization. Linnaeus used seven taxons:
KingdomPhylumClassOrderFamilyGenus
Species
Incr
easi
ng
sim
ilari
ties
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Problem with Linnaean System
• Due to convergent evolution, organisms that are quite different from each other evolve similar body structures.
• These similarities made it hard for taxonomist to classify many organisms accurately.
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CONVERGENT EVOLUTION
The process by which
unrelated organisms come to
resemble each other.
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• Scientist now understand that organisms share certain traits because of similarities in their evolutionary history.
• Biologist now group organisms into categories based on evolutionary descent rather than on physical similarities.
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• This evolutionary classification uses cladograms to show what characteristics organisms have in common.
• Scientists use cladograms to understand how things are similar and different.
• See page 452 and handout provided.
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A Cladogram
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Similarities in DNA and RNA
• The similarities of genes in DNA and RNA are now used to help determine classification.
• See handout provided.
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Activity: The Six-Kingdom Classification System
• The current classification system now has six kingdoms and three domains.
• Refer to the classification handout provided.
• Record a brief description of each domain and each kingdom on the handout.
• See page 458 in your textbook for descriptions.
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ACTIVITIES
“Amino Acid Activity”
“Using and Constructing a Classification Key”
“How to Read a Cladogram”
“Investigating Common Functions Among Diverse Organisms”
“Introduction to Viruses” – How do viruses fit into the classification scheme?