Overview
This lecture introduces the topic of biological classification, covering its importance, historical systems, and details up to the five-kingdom classification and characteristics of Kingdom Monera for NEET biology preparation.
Importance of Classification
- Classification helps organize living organisms to make their study manageable.
- Early classifications were based on external features for human benefit, not science.
Historical Approaches to Classification
- Aristotle is credited as the first to attempt scientific classification using morphological traits.
- Aristotle classified plants by height (trees, shrubs, herbs) and animals by presence of red blood cells (RBCs).
- Linnaeus introduced binomial nomenclature, systematics (phylogenetic basis), and two-kingdom classification (Plantae, Animalia), based on cell wall presence.
Limitations of Early Classification Systems
- Two-kingdom system failed to distinguish between prokaryotes/eukaryotes, unicellular/multicellular, and photosynthetic/non-photosynthetic organisms.
- Grouped together widely different organisms (bacteria, fungi, plants) just due to the presence of cell wall.
Modern Classification Systems
- R.H. Whittaker proposed the five-kingdom classification in 1969: Monera, Protista, Fungi, Plantae, Animalia.
- Classification is based on cell type, cell wall, nuclear membrane, mode of nutrition, and body organization (C2 N2 B).
- Carl Woese introduced the three-domain (six-kingdom) system: Bacteria, Archaea, Eukarya.
Five Kingdoms and Their Criteria
- Monera: prokaryotic, unicellular, cell wall (peptidoglycan), autotrophic/heterotrophic, mainly asexual reproduction.
- Protista: unicellular eukaryotes, variable cell wall, mostly aquatic.
- Fungi: eukaryotic, multicellular (except yeast), cell wall (chitin), heterotrophic, saprophytic.
- Plantae: eukaryotic, multicellular, cell wall (cellulose), autotrophic.
- Animalia: eukaryotic, multicellular, no cell wall, heterotrophic.
Kingdom Monera Details
- Includes all prokaryotes (bacteria, cyanobacteria/blue-green algae, archaebacteria).
- Bacteria shapes: coccus (spherical), bacillus (rod), vibrio (comma), spirillum (spiral).
- Bacterial cell wall made of peptidoglycan; may be motile with flagella (flagellin protein).
- Bacteria can be autotrophic (photosynthetic—e.g., cyanobacteria; chemosynthetic) or heterotrophic (parasites, saprophytes).
- Archaebacteria live in extreme conditions: halophiles (salt), thermophiles (heat), methanogens (anaerobic, produce methane).
- Cyanobacteria are photosynthetic, have chlorophyll a, form colonies, and fix nitrogen via heterocysts (e.g., Nostoc, Anabaena).
- Most bacteria reproduce by binary fission; under harsh conditions, spores form; conjugation allows DNA transfer.
- Mycoplasma: smallest living cell, lacks cell wall, survives without oxygen, called "joker" of plant kingdom.
Key Terms & Definitions
- Morphological characters — external features used for classification.
- Prokaryote — cell without a membrane-bound nucleus or organelles (e.g., bacteria).
- Eukaryote — cell with membrane-bound nucleus and organelles.
- Autotroph — organism that produces its own food.
- Heterotroph — organism that depends on others for food.
- Saprophyte — organism feeding on dead matter.
- Parasite — organism living on/in a host, causing harm.
- Archaebacteria — prokaryotes living in extreme environments.
- Cyanobacteria — photosynthetic bacteria, also called blue-green algae.
- Heterocyst — specialized cell in cyanobacteria for nitrogen fixation.
- Mycoplasma — wall-less, oxygen-tolerant tiny prokaryotes.
Action Items / Next Steps
- Revise five-kingdom classification table (criteria and examples).
- Learn bacterial shapes with examples.
- Read NCERT sections on classification and Kingdom Monera.
- Complete homework: write examples for each bacterial shape.
- Next lecture: study Protista and Fungi (Monday, 2:30 PM).