bioed online biological classification. why do we classify organisms? biologists group organisms to...
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BioEd Online
Biological
Classification
Why Do We Classify Organisms?
Biologists group organisms to organize and communicate information about their diversity, similarities and proposed relationships.
Classification systems change with expanding knowledge about new and well-known organisms.
Approximately 1.75 million species have been classified so far.
Tacitus bellus
History of Classification
Aristotle (2000 + y.a.) classified organisms as either plants (by size) or animals (red-blooded or not).
History of ClassificationIn the 1700s and 1800s: Carolus Linnaeus, a Swedish botanist, used similarities and
differences in morphology and behavior to classify birds. Linnaeus developed the first taxonomy system and made it
possible to include evolutionary principles in classification in the 1800s.
Jean-Baptiste Lamarck, Charles Darwin, and Ernest Haeckel introduced classification systems based on evolutionary relationships to organize biological diversity.
Carolus von Linnaeus(1707-1778)
Swedish scientist who laid foundation for modern taxonomy
Scientific Names
Carolus von Linnaeus devised the currently used binomial nomenclature.
Two-word naming system: Genus
Noun, Capitalized, Underlined or Italicized
Species Descriptive, Lower Case,
Underlined or Italicized
Ex.:Genus: Homo or HomoSpecies: sapiens or sapiensComplete scientific name of species:
Homo sapiens or Homo sapiensAbbreviated form: H. sapiens or H.
sapiens
Hierarchical Classification into Taxa
Taxonomists classify organisms by dividing them into smaller groups based on more specific criteria. A named groups of organisms is a taxon.
Taxonomic categories (taxa): Kingdom King Phylum Philip Class Came Order Over Family For Genus Green Species Spaghetti
Beginning with species, each category becomes progressively more comprehensive. Ex.: while the leopard, tiger and domestic cat all belong to different genera, they are grouped together in the same family.
Modern Classification - Species Concepts
Populus tremuloidesQuaking Aspen
Modern Classification Systems / Disciplines of Biology
Systematics is the branch of biology concerned with the study of biological diversity.
Taxonomy is the part of systematics concerned with identifying, naming, and classifying species based on morphological and behavioral similarities and differences.
Binomial Nomenclature is used to name species using two words, genus and species.
SystematicsEvolutionary Classification of Biodiversity
Systematics is the study of the evolution of biological diversity, and combines data from the following areas:
Fossil record Comparative homologies, morphological
characters (traits) derived from common ancestry
Cladistics, the study of evolutionary relationships between species based on shared characters (inherited traits)
Biochemical characters, such as comparative sequencing of DNA/RNA among organisms
Molecular clocks
Comparing Morphological Characters
A Molecular Clock
The rate at which mutations occur varies depending on:
•Type of mutation•Location of mutation in the genome•Type of protein affected•Population in which the mutation occurs
This inconsistency makes molecular clocks difficult to read.
Molecular clocks are often used along with the fossil record and help determine when a species evolved.
Taxonomic Diagrams based on Phylogeny
Mammals Turtles Lizards and Snakes
Crocodiles Birds Mammals Turtles Lizards and Snakes
Crocodiles Birds
Cladogram:a branched diagram that
shows the proposed phylogeny (evolutionary
history) of a species; nodes represent common ancestors
Phylogenetic Tree:a form of
cladogram; nodes represent common
ancestors
Lily Cladogram
The closer two groups are, the larger the number of characters they share.
Dichotomous Keys Identify Organisms
Dichotomous keys are tools used to identify organisms; field guides contain dichotomous keys.
Dichotomous keys contain pairs of contrasting descriptions - choices between two options.
After each description, the key directs the user to another pair of descriptions or identifies the organism.
Example (identifying a plant using its leaf): 1. a) Is the leaf simple? Go to 2
b) Is the leaf compound? Go to 3
2. a) Are margins of the leaf jagged? Go to 4b) Are margins of the leaf smooth? Go to 5
Kingdoms and Domains
Bacteria Archaea Eukarya
Bacteria Archaea Protista Plantae Fungi Animalia
Monera Protista Plantae Fungi Animalia
The three-domain system
The six-kingdom system
The traditional (now outdated) five-kingdom system
Classification – “All in the Family” at pbs.org