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Biological Classification BioEd Online 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 Classification In 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. Scientific Names Carolus von Linnaeus devised the currently used binomial nomeclature. Two-word naming system: Genus Noun, Capitalized, Underlined or Italicized Species Descriptive, Lower Case, Underlined or Italicized Ex.: Genus: Homo or Homo Species: sapiens or sapiens Complete scientific name of species: Homo sapiens or Homo sapiens Abbreviated form: H. sapiens or H. sapiens Carolus von Linnaeus (1707-1778) Swedish scientist who laid foundation for modern taxonomy 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 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 Nomeclature is used to name species using two words, genus and species. Populus tremuloides Quaking Aspen Systematics Evolutionary 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 Phylogenetic Tree: a form of cladogram; nodes represent common ancestors 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 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 4 b) Are margins of the leaf smooth? Go to 5 Kingdoms and Domains The three-domain system Bacteria Archaea Eukarya The six-kingdom system EuBacteria Archaeabact eria Protista Plantae Fungi Animalia Fungi Animalia The traditional (now outdated) five-kingdom system Monera Protista Plantae Kingdom Eubacteria (Domain Bacteria) Prokaryotes whose cell walls contain peptidoglycan, a protein-sugar polymer that is porous and strong All unicellular, mostly heterotrophic, some autotrophic Disease-causing bacteria and many harmless bacteria found in the environment are in this kingdom Kingdom Archaebacteria (Domain Archaea) Prokaryotes, thought to be more ancient than bacteria, no peptidoglycan in cell walls All unicellular, mostly heterotrophic, some autotrophic (including chemotrophic) Called “extremophiles” because they can live in the most extreme environments on earth, such as hot springs, salty lakes, thermal vents on the ocean floor, and the mud of marshes * All bacteria reproduce asexually (binary fission), many also sexually (conjugation) * Kingdom Protista Eukaryotes that differ significantly from each other but do not fit into any other kingdom Unicellular, colonial, or multicellular organisms, but their cells cannot form true tissues/organs Autotrophic or heterotrophic Reproduce sexually and asexually using spores, cysts, gametes Classified into three groups by trophism: fungus-like, plant-like, and animal-like Kingdom Fungi Eukaryotes whose cells can form true tissues / organs Cell walls contain chitin, a rigid polymer that gives structural support All heterotrophic / decomposers – secrete digestive enzymes onto their food and absorb the nutrients (extracellular digestion) Most multicellular, a few unicellular (yeasts); all sessile (cannot move) Reproduce sexually and asexually by spores, fragmentation/regeneration A mushroom is a fungus. Kingdom Plantae Eukaryotes whose cells can form true tissues / organs Autotrophs - form the basis of all land ecosystems – and a few heterotrophs (yes, some plants are parasites!) All multicellular and sessile (cannot move) Reproduce sexually and asexually (spores, seeds, cuttings, etc.) A leaf is a plant organ. Kingdom Animalia Eukaryotes whose cells form true tissues / organs All multicellular All heterotrophic Most motile (can move) Most reproduce sexually, some asexually