Biological Classification

Lecture by Ayushi Agarwal, Botany Expert at Physics Wallah

Introduction

• Continuation of the first chapter, Living World.
• Focus: How organisms are classified after identification.
• Importance: Understanding biodiversity (~17-18 lakh species).
• Usefulness: This knowledge helps in exploiting organisms for food, shelter, and clothing.

Early Classification

Aristotle

• Divided organisms into:
  • Plants
    • Subdivided by size: Herbs, Shrubs, Trees
  • Animals
    • Based on the presence of RBCs: Enema (with RBCs), Anima (without RBCs)

Linnaeus

• First formal classification system: Two Kingdoms
  • Kingdom Plantae
    • Features: Cell wall present, can’t move, non-motile, sedentary
  • Kingdom Animalia
    • Features: No cell wall, can move, motile
• Key Features Considered: Cell wall, ability to eat, ability to move, response to stimuli, contractile vacuole

Debates and Improved Classifications

Issues with Linnaean Classification:

1. Bacteria (prokaryotic) grouped with eukaryotic organisms.
2. Unicellular and multicellular organisms kept together.
3. Autotrophic and heterotrophic organisms grouped together.

Haeckel's Three Kingdom System:

• Third Kingdom: Protista (includes all unicellular eukaryotes)
• Kingdoms: Animalia, Plantae, Protista

Copeland's Four Kingdom Classification:

• Fourth Kingdom: Monera (prokaryotic organisms, e.g., bacteria)
• Kingdoms: Animalia, Plantae, Protista, Monera

Whittaker's Five Kingdom Classification:

• Fifth Kingdom: Fungi (removed from Plantae)
• Features Considered: Mode of nutrition, body organization, cell type, reproduction, nuclear membrane presence, phylogeny
• Kingdoms: Animalia, Plantae, Fungi, Protista, Monera

Woese’s Three Domain System:

• Divided into domains based on 16S rRNA gene sequencing:
  • Archaea: Kingdom Archaebacteria
  • Bacteria: Kingdom Eubacteria
  • Eukarya: Kingdoms Protista, Fungi, Plantae, Animalia

Detailed Study of Kingdoms

Kingdom Monera

• Types: Bacteria (Sole members)
• Cellular Structure: Prokaryotic, no well-defined nucleus, non-membrane-bound organelles.
• Respiration: Obligate aerobes, obligate anaerobes, facultative aerobes, facultative anaerobes.
• Nutrition: Autotrophic (photolithoautotroph, chemolithoautotroph), heterotrophic (majorly decomposers).
• Reproduction: Asexual by fission; no true sexual reproduction.
• Examples: Archaebacteria (Methanogens, Halophiles, Thermoacidophiles), Eubacteria (Mycoplasma, Cyanobacteria)

Kingdom Protista

• General Features: Unicellular eukaryotic organisms, aquatic.
• Reproduction: Both asexual (fission, fragmentation) and sexual (gamete formation, alternation of generations).
• Classification: Based on nutrition
  • Producer Protists: Diatoms, Dinoflagellates, Euglenoids
  • Consumer Protists: Slime Molds
  • Protozoans: Amoeboid, Flagellated, Ciliated, Sporozoans

Kingdom Fungi

• General Features: Multicellular eukaryotic organisms, chitinous cell wall, terrestrial.
• Reproduction: Vegetative (fragmentation), asexual (spores), sexual (gamete formation, zygote).
• Classification: Based on spore formation
  • Phycomycetes (Oomycetes, Zygomycetes)
  • Ascomycetes
  • Basidiomycetes
  • Deuteromycetes (Fungi Imperfecti)

Kingdom Plantae and Animalia

• Plantae and Animalia: Detailed study in separate chapters.

Organisms Outside Five Kingdoms

Viruses

• Not in 5 Kingdoms: Acellular, connecting link between living and non-living.
• Properties: Genetic material (DNA/RNA), mutation, presence of enzymes.
• Types: Tobacco Mosaic Virus (TMV), Bacteriophage.
• Subviral Agents: Viroids, Virusoids, Prions.

Lichens and Mycorrhizae

• Lichens: Mutual association between algae (phycobiont) and fungi (mycobiont). Air pollution indicator.
• Mycorrhizae: Mutual association between fungi and higher plant roots. Helps in absorbing water and minerals.

Conclusion

• Recap: The importance and application of biological classification in understanding biodiversity.
• Next Steps: Dive deeper into the study of each kingdom, focusing on unique characteristics and examples.

Questions

1. Founder of Five Kingdom Classification?
   • Answer: Whittaker
2. Function of heterocysts in cyanobacteria?
   • Answer: Nitrogen Fixation

Stay tuned for the next chapter: Plant Kingdom.