Biological Classification

• Introduction & History

  • Aristotle's Classification
    • Plants (Trees, Shrubs, Herbs)
    • Animals (Red blood cells present/absent)
  • Two-Kingdom System
    • Proposed by Carolus Linnaeus
    • Plantae and Animalia
    • Limitations (Didn't distinguish eukaryotes/prokaryotes, unicellular/multicellular)
  • Five-Kingdom Classification
    • Proposed by R.H. Whittaker (1969)
    • Criteria: Cell structure, thallus organization, mode of nutrition, reproduction, phylogenetic relationships

• Kingdom Monera

  • General Characteristics
    • Sole members are bacteria
    • Prokaryotic, unicellular
    • Lack true nucleus and membrane-bound organelles
  • Shapes of Bacteria
    • Coccus (Spherical)
    • Bacillus (Rod-shaped)
    • Vibrio (Comma-shaped)
    • Spirillum (Spiral)
  • Archaebacteria
    • Live in extreme habitats
    • Halophiles (Salty areas)
    • Thermoacidophiles (Hot springs)
    • Methanogens (Marshy areas, biogas production)
  • Eubacteria (True Bacteria)
    • Rigid cell wall, often flagellated
    • Cyanobacteria (Blue-green algae, photosynthetic, possess heterocysts for nitrogen fixation)
    • Chemosynthetic Autotrophs (Recycle nutrients like nitrogen, iron, sulfur)
    • Heterotrophic Bacteria (Decomposers, pathogenics, useful in curd/antibiotics)
  • Mycoplasma
    • Completely lack cell wall
    • Smallest living cells known
    • Pathogenic in plants and animals

• Kingdom Protista

  • General Characteristics
    • Single-celled eukaryotes
    • Primarily aquatic
  • Chrysophytes
    • Diatoms and golden algae (desmids)
    • Cell walls form overlapping shells (diatomaceous earth)
    • Chief producers in oceans
  • Dinoflagellates
    • Mostly marine, photosynthetic
    • Stiff cellulosic plates
    • Cause red tides (e.g., Gonyaulax)
  • Euglenoids
    • Fresh water, stagnant water
    • Protein-rich layer called pellicle (instead of cell wall)
    • Mixotrophic (photosynthetic in sunlight, heterotrophic in dark)
  • Slime Moulds
    • Saprophytic protists
    • Form aggregation called plasmodium under favorable conditions
  • Protozoans
    • Heterotrophs (predators or parasites)
    • Amoeboid (e.g., Amoeba, Entamoeba)
    • Flagellated (e.g., Trypanosoma)
    • Ciliated (e.g., Paramecium)
    • Sporozoans (e.g., Plasmodium)

• Kingdom Fungi

  • General Characteristics
    • Heterotrophic, cosmopolitan
    • Body consists of long, slender threads called hyphae (network = mycelium)
    • Cell wall made of chitin and polysaccharides
    • Saprophytic, parasitic, or symbiotic (Mycorrhiza, Lichens)
  • Reproduction
    • Vegetative: Fragmentation, fission, budding
    • Asexual: Conidia, sporangiospores, zoospores
    • Sexual: Oospores, ascospores, basidiospores
    • Sexual cycle steps: Plasmogamy $\rightarrow$ Karyogamy $\rightarrow$ Meiosis
  • Classes of Fungi
    • Phycomycetes
      • Aquatic, aseptate and multinucleate hyphae (coenocytic)
      • Example: Mucor, Rhizopus (bread mould)
    • Ascomycetes (Sac Fungi)
      • Branched and septate hyphae
      • Spores produced endogenously in ascii
      • Example: Aspergillus, Claviceps, Neurospora, Yeast
    • Basidiomycetes (Club Fungi)
      • Branched and septate hyphae
      • Spores produced exogenously on basidium
      • Example: Mushrooms, Ustilago (smut), Puccinia (rust)
    • Deuteromycetes (Fungi Imperfecti)
      • Only asexual/vegetative phases known
      • Example: Alternaria, Colletotrichum, Trichoderma

• Kingdom Plantae

  • General Characteristics
    • Eukaryotic, chlorophyll-containing organisms (plants)
    • Autotrophic (mostly)
    • Alternation of generation (sporophytic and gametophytic phases)
  • Groups
    • Algae, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms

• Kingdom Animalia

  • General Characteristics
    • Eukaryotic, multicellular, heterotrophic
    • Lack cell walls
    • Directly or indirectly dependent on plants for food
    • Holozoic nutrition (ingestion of food)
    • Definite growth pattern into adults

• Viruses, Viroids, Prions & Lichens (Acellular/Sub-viral Agents)

  • Viruses
    • Non-cellular, inert outside host cell, obligate parasites
    • Discovered by D.J. Ivanowsky (Term Virus given by M.W. Beijerinck)
    • Structure: Protein coat (capsid) made of capsomeres enclosing genetic material (DNA or RNA)
    • Diseases: Mumps, smallpox, herpes, influenza, AIDS
  • Viroids
    • Discovered by T.O. Diener (1971)
    • Free infectious RNA (lack protein coat)
    • Smaller than viruses (e.g., Potato spindle tuber disease)
  • Prions
    • Abnormally folded protein infectious agents
    • Neurological diseases (e.g., BSE / Mad cow disease, Cr-Jacob disease)
  • Lichens
    • Symbiotic associations between algae (phycobiont) and fungi (mycobiont)
    • Algae prepare food; fungi provide shelter and absorb minerals
    • Excellent pollution indicators (do not grow in polluted areas)