5.1

• Diversity of Life


  The study of the variety of living organisms and how they are classified
• Aristotle's classification system

  First to classify organisms almost 2000 years ago<|>Divided organisms into plants and animals<|>Classified animals into land dwellers, water dwellers, and air dwellers<|>Classified plants into herbs, shrubs, and trees
• Flaws of Aristotle's classification system?

• Linnean classification system

  Placed organisms in groups based on structural similarity<|>Assigned scientific names using binomial nomenclature
• Two-kingdom system


  Divided all organisms into plant and animal kingdoms<|>Each kingdom was further subdivided into smaller groups like phyla and classes
• Limitations of the two-kingdom system:
• Three-kingdom system


  Kingdoms: Protista, Plantae, Animalia<|>Based on morphological complexities, tissue systems, division of labor, and mode of nutrition
• Four-kingdom system


  Added kingdom Monera for prokaryotic protists (bacteria and blue-green algae)<|>Retained eukaryotic protists (algae, fungi, protozoa) in kingdom Protoctista
• Reason for challenge in classifying unicellular organisms:
• Five-kingdom system


  Evidence that all living things fall into three broad groups
• Three-domain system / Six-kingdom system


  Domains are taxonomic levels higher than kingdoms<|>Domains: Bacteria, Archaea, Eukarya<|>Kingdoms: Eubacteria, Archaebacteria, Protista, Plantae, Fungi, Animalia
• Reason for domains as higher taxonomic level:
• Differences between the three domains

  Bacteria: prokaryotic, Archaea: prokaryotic, Eukarya: eukaryotic
• Eight-kingdom system


  Protista kingdom was too diverse, so it was further divided into better-defined kingdoms
• Kingdoms in the eight-kingdom system

  • Archaebacteria
  • Eubacteria
  • Protozoa
  • Animalia
  • Plantae
  • Fungi
  • Chromista
  • Archezoa
• Kingdom Monera (Archaebacteria, Bacteria, Cyanobacteria)


  • Smallest organisms, no nuclear membrane or membrane-bound organelles
  • Photosynthetic pigments in chromatophores, respiratory enzymes in mesosomes
  • Absorptive, chemosynthetic, photoheterotrophic, or photoautotrophic nutrition
  • Cell walls made of peptidoglycan or protein
  • Flagella lack 9+2 arrangement, ribosomes 70S
  • Asexual reproduction, parasexual recombination
• Distribution of monerans:
• Kingdom Protista


  • Eukaryotic, unicellular or colonial, no tissue/organ differentiation
  • Aquatic, photosynthetic (phytoplankton) or non-photosynthetic (zooplankton)
  • Absorptive, photosynthetic, or ingestive nutrition
  • Possess membrane-bound organelles like mitochondria, lysosomes, centrioles
  • Genetic material in true nucleus, 11-stranded flagella with 9+2 arrangement
  • Reproduce sexually and asexually
• Kingdom Fungi


  • Ubiquitous, highly adaptable, heterotrophic and absorptive
  • Filamentous vegetative body (hyphae) with cell walls made of chitin
  • No root-shoot differentiation or specialized transport vessels
  • Reproduce asexually and sexually using spores
  • Store glycogen as reserve food material
• Economic importance of fungi:
• Kingdom Plantae


  • Primarily autotrophic, some heterotrophic or saprophytic
  • Multicellular organisms with walled and vacuolate eukaryotic cells
  • Autotrophic through photosynthesis using chlorophyll pigments
• Heterotrophic


  Absorb food from the environment, extracellular digestion
• Vegetative body of fungi


  • Filamentous, hypha, thread-like, branched, cell wall
• Vegetative body of fungi is never differentiated into root, shoot, and specialized vessels for internal transport of nutrients
• Cell wall of fungi is mainly constituted of chitin
• Reproduction of fungi


  Usually asexual and sexual by means of asexual and sexual spores
• Reserve food material in fungi

  Glycogen (animal starch)
• Kingdom Plantae (Macroalgae and Plants) are primarily autotrophic, some heterotrophic, a few saprophytic
• Organisms in Kingdom Plantae

  • Multicellular (except some algae; plant-like protists) with walled and frequently vacuolate eukaryotic cells
  • Autotrophic by means of photosynthesis; photosynthetic pigments are chlorophylls present in plastids (chloroplasts)
  • Reproduction primarily sexual, with haploid and diploid stages alternating with each other (alternation of generations)
  • Food reserve is usually starch and fat
  • Growth is usually indefinite; growing points are well-defined
• Individuals in Kingdom Animalia

  • Multicellular with wall-less eukaryotic cells
  • Multi-cellularity accompanied by cellular tissue and organ-system levels of an organization with complex cell junctions
  • Nutrition is primarily ingestive with digestion in an internal cavity, but some forms are absorptive and some lack a digestive cavity
  • Reproduction mainly sexual with meiosis forming gametes; haploid stages other than gametes almost lacking above lowest phyla
  • Zygote develops into an embryo
  • Animals are motile or mobile (except sponges)
  • Tissues and organ system complexity
• Phylogeny


  The evolutionary history of an organism
• Phylogenetic tree


  A type of family tree that depicts the evolutionary relationships between various groupings of species
• Evidences used for modern taxonomy

  • Morphology (Structural Similarities)
  • Cellular Organization
  • Evolutionary Relationships
  • Biochemical similarities
  • Genetic similarities
  • Embryological similarities
• Dichotomous key


  A useful scientific tool for identifying various organisms based on their observable characteristics, made up of a series of statements, each with two options, that guide users to the proper identification
• Linnaeus proposed the 2-Kingdom system of classification
• Microscopic observations and other modern techniques added up to the knowledge, thus, modifying the early classification systems
• A dichotomous key is a scientific tool made up of a series of statements, each with two options, that guide users to the proper identification
• Embryological similarity evidence investigates the features of embryos and their development, and how their resemblances across species indicate relatedness
• Molecular clocks


  Used to plot the period and time that organisms are related by the identification of repeating occurrences of mutations present in the genes