Chapter 18 Classification Why Classify Human nature we
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Chapter 18 Classification
Why Classify? ? • Human nature- we love to put things in their place! • Organization • Identification • Less Confusion • Show Relationships
Taxonomy • The branch of biology that names and groups organisms according to their characteristics and evolutionary history. • Classify the thousands of new species discovered each year. • 1. 5 million so far • ? ? millions yet to be discovered.
• Biologists use the characteristics of newly discovered species to classify it with organisms having similar characteristics. • The way we group organisms today continues to change and reflect the evolutionary history of organisms.
Early Systems of Classification • Aristotle • Linnaeus
Aristotle • Greek Philosopher 384 -322 BC • First classified organisms more than 2000 yrs ago as either plants or animals. –Animals: land dwellers, water dwellers, or air dwellers. –Plants: three categories based on differences in their stems.
Carolus Linnaeus • Father of Taxonomy • Swedish naturalist • 1707 -1778 • 100 years before Darwin!
• 1735 – published Systema Naturae. • Devised a system of grouping organisms into hierarchical categories. • Used an organism’s morphology (form and structure) – it’s appearance
Levels of Classification Kingdom Phylum or Division Class Order Family Genus Species
• Under the modern Linnaean system, the classification of an organism places the organism within a nested hierarchy of taxa. (taxon – singular)
Binomial Nomenclature • Scientific Name has two parts. – 1 st part is the genus – 2 nd part is the species which is the identifier or descriptive word. • Genus name is capitalized and both names are underlined or written in italics.
• Latin used by all scientists as a standard. • Linnaeus classified 1000’s of organisms. • Versions of his system are still used today.
Scientific Names • May describe the organism, suggest geographic range, or honor a person • Homo sapiens (homo = man sapiens = wise) • Chaos chaos (amoeba never appear the same shape)
Linnaea borealis (Linnaeus’ favorite, borealis = northern)
• Lupinus texensis • Texas bluebonnet
Phylogeny • Phylogeny is evolutionary history • Much of Linnaeus’ work in classification is relevant even in the context of phylogeny because morphological features are largely influenced by genes and are clues of common ancestry.
Evolutionary Classification • Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities • Phylogeny – the study of evolutionary relationships
Modern taxonomic placement involves: • Morphology • Chromosomal characteristics • Nucleotide and amino acid sequences (chromosomes) • Embryological development • Information from the fossil record.
Phylogenetic tree • Family tree that shows the evolutionary relationships thought to exist among groups of organisms. • Represents a hypothesis and is based on several lines of evidence. • Subject to change as new information arises.
Interpreting a Phylogenetic Tree • Organism at base of tree is common ancestor to all the others in the tree. • Branch points indicate the evolution of some characteristic that splits a group into two groups. • Groups shown at tips of branches include organisms that have evolved most recently.
Molecular Clocks • This model uses comparisons of DNA, RNA and proteins to estimate the length of time that two species have been evolving independently. • The degree of dissimilarity is, in turn and indication of how long ago the two species shared a common ancestor.
DNA comparisons (Artic bluegrass)
DNA banding patterns
Cladistics • Relatively new system of phylogenetic classification. • Uses certain features of organisms called shared derived characteristics to establish evolutionary relationships.
• Derived character: feature that apparently evolved only within the group under consideration. Example: feathers in birds are inherited from a common ancestor.
To interpret a cladogram: • Begin at the bottom and move up the axis that shows branch points. • Groups and derived characteristics appeared in the order shown. • Example: all groups branching above “lungs” have lungs. Those below do not.
Two Modern Systems of Classification • Six Kingdom System • Three Domain System
Six Kingdom System • • • Kingdom Archaebacteria Kingdom Eubacteria Kingdom Protists Kingdom Fungi Kingdom Plantae Kingdom Animalia
Kingdom Archeabacteria • • Prokaryotic Unicellular Cell walls (without peptidoglycan) Autotroph or heterotroph
Kingdom Archaebacteria • Some autotrophic – produce food by chemosynthesis and methane waste. • “archae” = ancient • May be directly descended from and very similar to first organisms on Earth
• Can withstand extreme conditions –Thermophiles (heat) –Halophiles (salt) –Methanogens (methane gas) • Many live in harsh environments – sulfurous hot springs, salty lakes, anaerobic environments, intestines of animals.
Kingdom Eubacteria • • • “eu” = true Prokaryotic Unicellular Cell walls (with peptidoglycan) Autotroph or heterotroph
• Bacteria that affect your life: tooth decay, turn milk to yogurt, food poisoning, illness • Most use oxygen, but a few cannot live in O 2 • Both Eubacteria and archaebacteria make up the greatest number of living things on Earth.
• Eubacteria and archaebacteria reproduce by binary fission but do have methods of genetic recombination to allow evolution to occur. • Short generation times (30 minutes) allow rapid evolutionary response to environmental change. Example: antibiotic resistant bacterial infection.
Kingdom Protista • Eukaryotic • Cell walls of cellulose • Mostly single-celled organisms, but some multicellular but lack specialized tissues • Autotrophic and heterotrophic • Include Protozoa and Algae
• Many species distantly related. • Broad kingdom contains all eukaryotes that are not plants, animals, or fungi. 50, 000 species. • Sexual cycles of many are unknown but thought to have some process of genetic recombination.
Kingdom Fungi • • • Unicellular and multicellular Eukaryotic Cell walls of chitin Heterotrophic Absorb nutrients rather than ingesting • 100, 000 species – mushrooms, yeast, mildews, and molds.
• Sexual cycles not known for many fungi. It is likely that all species have some way of promoting genetic recombination.
Kingdom Plantae • Multicellular plants • All except for a few parasitic forms are autotrophic and use photosynthesis as a source of energy • Eukaryotic • Most live on land • Sessile – don’t move around
• Most have a sexual cycle based on meiosis • 350, 000 species identified including mosses, ferns, conifers, flowering plants.
Kingdom Animalia • Eukaryotic • Heterotrophs • Multicellular • No cell walls • Most have symmetrical body organization • Move about their environment • Have a sexual cycle based on meiosis • About 1, 000 species
Three Domain System • Molecular biology has led to an alternative to the 6 kingdom system • Comparing sequences of ribosomal RNA in many organisms. Estimated how long ago pairs of organisms shared a common ancestor.
• Phylogenetic tree drawn from this data shows that living things seem to fall naturally into 3 broad groups or domains.
The Three Domains (and the kingdoms they include) • Bacteria (Eubacteria) • Archaea (Archaebacteria) • Eukarya (Eukaryotes): includes Protista, Fungi, Plantae, Animalia
Conclusions from the Three Domain System • All eukaryotes have true nuclei with linear chromosomes and membrane-bound organelles. • The most variation in Eukarya is among protists.
• When considered from the perspective of the complete diversity of life on Earth, the fungi, plants, and animals are quite similar to each other.