1.2 Biological Classification

Three Domains of Life

• Domain Bacteria: Prokaryotic cells with peptidoglycan in their cell walls.
• Domain Archaea: Prokaryotic cells without peptidoglycan, often found in extreme environments.
• Domain Eukarya: Eukaryotic cells with a true nucleus and membrane-bound organelles.

Five-Kingdom System

• Kingdom Monera: Unicellular prokaryotes (Bacteria, Archaea).
• Kingdom Protista: Unicellular eukaryotes.
• Kingdom Fungi: Multicellular, heterotrophic, with chitin cell walls.
• Kingdom Plantae: Multicellular, autotrophic, with cellulose cell walls.
• Kingdom Animalia: Multicellular, heterotrophic, without cell walls.

Kingdom Monera

• Characteristics: Prokaryotic, unicellular, diverse nutrition.
• Classification of Bacteria:
  • Shape: Coccus, Bacillus, Spirillum, Vibrio.
  • Nutrition: Autotrophic or Heterotrophic.
  • Respiration: Aerobic or Anaerobic.
• Gram Staining: Differentiates bacteria based on cell wall composition (Gram-positive vs. Gram-negative).

Kingdom Protista

• Characteristics: Eukaryotic, mostly unicellular, diverse.
• Subgroups:
  • Chrysophytes: Diatoms and golden algae.
  • Dinoflagellates: Cause red tides.
  • Euglenoids: Mixotrophic.
  • Slime Moulds: Saprophytic.
  • Protozoans: Amoeboid, Flagellates, Ciliates, Sporozoans.

Kingdom Fungi

• Characteristics: Eukaryotic, heterotrophic, chitin cell walls.
• Reproduction: Asexual (spores) and Sexual (plasmogamy, karyogamy, meiosis).
• Classes:
  • Zygomycetes: Bread molds.
  • Ascomycetes: Sac fungi (yeast, penicillin).
  • Basidiomycetes: Club fungi (mushrooms).
  • Deuteromycetes: Imperfect fungi.

Viruses, Viroids, and Prions

• Viruses:
  • Obligate intracellular parasites.
  • Genetic material (DNA or RNA) in a protein capsid.
  • Link between living and non-living.
• Viroids:
  • Infectious RNA molecules without a capsid.
  • Cause plant diseases.
• Prions:
  • Infectious protein particles.
  • Cause neurodegenerative diseases (e.g., Mad Cow Disease).