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Chapter 20 Classification of Living Things

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  1. Chapter 20Classification of Living Things

  2. Taxonomy – Science of Classification • Branch of biology concerned with identifying, describing and naming organisms. • Ideally, classification is based on our understanding of how organisms are related to one another through evolution • Not an artificial system

  3. Taxonomy - History • Began with Greeks and Romans • Aristotle - first taxonomic system • Plants: trees, shrubs, and herbs • Animals: air-dwellers, water-dwellers, land-dwellers • System flawed because scientifically valid characteristics were often not used in determining the categories.

  4. Carolus Linnaeus (Sweedish botanist)father of modern taxonomy (1707- 1778) • Eliminated use of common names • Used Latin as a basis for nomenclature • Created "binomial nomenclature" identifying each organism by a two-part name

  5. Linneaus, cont’d • Used morphological (form & structure) characteristics as a basis for classification • Linnaeus considered each species to have a unique structure that made it distinct

  6. Species name = Scientific name • e.g. Magnoliagrandifloraunderlined Magnolia grandiflora italicized • genus - Magnolia • specific epithet - grandiflora • species - Magnolia grandiflora M. grandiflora

  7. Created seven taxa for classification purposes: Kingdom………………………………..most inclusive Phylum Class Order “Classification Family Hierarchy” Genus Species…………….least inclusive • Taxon – a group of organisms that fills a particular category of classification

  8. Hierarchy of taxa for Callinectes sapidus Callinectes (Gk. Beautiful swimmer) sapidus (L. savory) Domain Eukarya (Eucaryota) Kingdom Animalia Phylum Arthropoda Class Malacostraca Order DecapodaAtlanticBlue Crab Family Portunidae Genus Callinectes Species Callinectes sapidus

  9. Classification of organisms • Additional levels of classification can be added by adding super-, sub-, or infra- (e.g., sub-order) – • Taxonomists – ‘lumpers’ or ‘splitters’

  10. Classification of organisms • the higher the classification category, the more inclusive it is • A character is any structural, chromosomal, or molecular feature that distinguishes one group from another. • members of a kingdom share generalcharacters; members of a species share quite specificcharacters

  11. * The Linnaean system of classification is still in use today. • * Linnaeus was devoutly religious, but his taxonomic system was later to be used to demonstrate the phylogenetic (evolutionary) relationships among living organisms. • * Linnaeus Latinized his own name from Carl von Linne’

  12. Some points about species • The biological definition of a species states a group of organisms capable of interbreeding and producing fertile offspring; they share the same gene pool. Distinguishing species on the basis of reproductive isolation can also be a problem. Some species do not reproduce sexually. Some species hybridize where their geographic ranges overlap. Reproductive isolation can be difficult to observe. • When a species has a wide geographic range, variant types may tend to interbreed where they overlap; these populations are called subspecies, and are designated by a three-part name.

  13. Genus name may include more than one species or sub-species Ursus americanus Ursus maritimus Ursus thibetanus binomial and trinomial Ursus arctos mittendorfii Ursus arctos horribilis

  14. Classification - an ongoing process • there are estimated to be between 3 and 30 million species living on earth • we have currently named one million species of animals and a half million plant and microorganismic species • some groups, such as birds, are nearly all known; some insect groups are mostly unknown

  15. Major kingdoms of life • Work of R.H. Whittaker (1969) • Five are generally recognized based on • Cell type • Organization • Nutrition

  16. Five Kingdoms of Life (KEY) • 1. Cell type: • A. Prokaryotic (P) - primitive, lack membrane-bound internal organelles • B. Eukaryotic (E) - true nucleus, membrane-bound organelles • 2. # Cells: • Unicellular (U) • Colonial (C) • Multicellular (M) • 3. Nutrition: • A. Autotrophic (A) - Source of carbon is simple, such as carbon dioxide (CO2) • B. Heterotrophic (H) - Source of carbon is complex, such as carbohydrates, proteins, lipids, or nucleic acids

  17. Kingdoms of Life • Many modern taxonomic systems split bacteria (Monera) into several different kingdoms. • Generally, • protists are considered to have evolved from monerans, and • the fungi, plants, and animals evolved from protists via three separate lineages.

  18. A higher category, the domain, has been proposed to be added to these 7 categories • Three-Domain System • sequencing of rRNA suggests all organisms evolved along three distinct lineages: domains • Bacteria • Archaea • Eukarya

  19. Three Domains 1. the bacteria diverged first; archaea and eukarya are more closely related than either is to bacteria       2. the archaea live in extreme environments: methanogens in anaerobic swamps, halophiles in salt lakes, and thermoacidophiles in hot acidic environments      the archaea cell wall is diverse but not the same as the bacterial cell wall       3. the eukarya contains unicellular to multicellular organisms, always with a membrane-bound nucleus 

  20. eukarya archaea bacteria

  21. Phylogenetic (Evolutionary) Trees • Systematics is the study of the diversity of organisms using information from cellular to population levels • (Cell, tissue, organ, organism, population) • A goal of systematics is to determine phylogeny • Phylogeny is the evolutionary history of a group of organisms • Evolution is a core theme of biology. • Evolution - the process by which life on earth has changed over time.

  22. Phylogenetic (Evolutionary) Trees • a phylogenetic tree indicates common ancestors and lines of descent or lineages an ancestral (primitive) character is a trait that is present in a common ancestor and all species in its lines of descent a derived character is present only in a specific line of descent • Different lineages diverging from a common ancestor have ancestral characteristics—traits shared by the ancestor and the species in its lines of descent.

  23. Simple phylogenetic tree (skeletal differences) (tree climbing)

  24. All give birth to live young (placental mammal)

  25. highly branched palmate hollow horns male/female solid horns (antlers) male only even-toed hoofs Classification and Phylogeny

  26. Tracing Phylogeny • Systematists use various methods used to discover evolutionary relationships between species. • If you can determine common ancestors, then you know how evolution occurred and you can classify organisms correctly.

  27. Fossil Record • because fossils can be dated, fossils can establish the age of a species •       most organisms decay and the chances of becoming a fossil are low

  28. Homology – morphological data • Homology is a character similarity that is due to having a common ancestor (anatomical and embryological features) homologous structures are related to each other through common descent but may differ in structure and function (e.g., the forelimbs of a horse and the wings of a bat) analogous structures have the same function but are not derived from the same organ in a common ancestor (e.g., the wings of an insect and the wings of a bat) • convergent evolution is acquisition of similar traits in distantly related lines of descent as a result of adaptation to similar environmental conditions   --both spurges and cacti are adapted to a hot, dry environment and are both similar, but details of flower structure indicate these two groups are not closely related • parallel evolution produces similar characters in related lineages without occurring in a common ancestor

  29. Molecular Data • Speciation (new species) occurs when mutations bring about changes in base pair sequences of DNA • Protein Comparisons • •       earlier studies used immunological reactions to antibodies, made by injecting a rabbit with cells of one species, to determine the relatedness of two species • •       we now use amino acid sequences to determine the differences in proteins between two species • •       cytochrome c is a protein found in all aerobic organisms; the amino acid differences in cytochrome c between chickens and humans is 13 but between chickens and ducks is only 3 • •       since the number of universal proteins is limited, most new studies use differences in RNA and DNA.

  30. RNA and DNA Comparisons •       all cells have ribosomes for protein synthesis; comparing rRNAbase pairsequences provides a reliable indicator of similarity between organisms •       Chimpanzees and Humans •       DNA DNA hybridization shows chimpanzees closer to humans than to other apes •       yet humans are kept in a separate family and chimpanzees are with the ape family due to differences in adaptation to the environment • Mitochondria DNA (mtDNA) changes ten times faster than nuclear DNA • •       mtDNA is often used for closely related species

  31. Phenogram–DNA data Length of branches indicates the relative number of nucleotide pair differences among species shown.

  32. Molecular Clocks •       When nucleic acid changes are not tied to adaptation - the fairly constant changes provide a "molecular clock“ to indicate relatedness and evolutionary time •       the fossil record can then be used to calibrate the clock and confirm the hypothesis drawn from molecular data

  33. Systematics today – 3 main schools • 1. Cladistic Systematics (Willi Hennig) • cladistics analyzes primitive and derived characters and constructs cladograms on the basis of shared derived characters (homologies) • cladogram: a diagram showing relationships among species based on shared, derived characters •       a clade is an evolutionary branch - that includes a common ancestor and all its descendent species (monophyletic taxon) • outgroup - taxon (taxa) that define the primitive characters of the study group; study group – taxa placed in a clade • Parsimony        cladists are guided by principle of parsimony: the minimum number of assumptions is most logical; that is, the fewest number of shared derived character are left unexplained

  34. Charcters of taxa being compared Cladogram w/ 3 clades monophyletic taxon Common ancestor – notochord in embryo Notochord- shared ancestral character; Others are shared derived characters

  35. Systematics today • 2. Phenetic Systematics •       phenetic systematists cluster species on the basis of the number of shared similarities, regardless of whether they might be convergent, parallel, or depend on one another •       results of their analysis are depicted in a phenogram •       phenograms vary for the same group of organisms, depending on how the data are collected and handled

  36. Systematics today • 3. Traditional Systematics •       traditional systematics stresses common ancestry and the degree of structural (anatomical) difference among divergent groups in order to construct phylogenetic trees • •       a monophyletic groupdoes not include all groups from all ancestors (as a clade does) •       cladists would not use "reptiles" because it does not include all organisms derived from reptiles

  37. Traditional vs. cladistic systematics Hair/ mammary glands scaly skin feathers Traditional view Cladistic view Common ancestor-egg layer