Overview
Chapter 2 'Biological Classification' explores the systematic classification of living organisms from Aristotle and Linnaeus to R.H. Whittaker's Five Kingdom System (1969). It details the diagnostic features, cell structure, nutrition, and reproduction of Kingdom Monera (Bacteria, Cyanobacteria, Mycoplasma), Kingdom Protista (Chrysophytes, Dinoflagellates, Euglenoids, Slime Moulds, Protozoans), Kingdom Fungi (Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes), Kingdom Plantae, Kingdom Animalia, and acellular entities (Viruses, Viroids, Prions, and Lichens).
Learning Objectives
- Trace the historical development of classification from Aristotle (2 Kingdoms) to R.H. Whittaker (5 Kingdoms).
- Compare the 5 Kingdoms across Cell Type, Cell Wall, Nuclear Membrane, Body Organisation, and Mode of Nutrition.
- Describe Kingdom Monera including Archaebacteria, Eubacteria, Heterocyst in Anabaena, and Mycoplasma.
- Detail Kingdom Protista categories: Chrysophytes (Diatoms), Dinoflagellates, Euglenoids, Slime Moulds, and Protozoans.
- Differentiate the 4 fungal classes (Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes) by spore formation and mycelium structure.
- Explain the structure and nature of Viruses (TMV, Bacteriophage), Viroids (T.O. Diener), Prions, and Lichens.
Topics in this chapter
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Systems of Classification & R.H. Whittaker's 5 Kingdoms
Fig 2.1 — High-Resolution Educational Poster: Whittaker's Five Kingdom Classification System (Monera, Protista, Fungi, Plantae, Animalia)
Five Kingdom System Criteria
5 Main Criteria used by Whittaker: (1) Cell Structure (Prokaryotic vs Eukaryotic), (2) Body Organisation (Unicellular vs Multicellular), (3) Mode of Nutrition (Autotrophic vs Heterotrophic), (4) Reproduction, (5) Phylogenetic (Evolutionary) Relationships.
Historical Background:
- Aristotle: Earliest scientific attempt. Classified plants into Trees, Shrubs, and Herbs based on simple morphological characters, and animals into two groups: those with red blood (Enaima) and those without red blood (Anaima).
- Linnaeus (Two Kingdom System): Divided all living organisms into Kingdom Plantae and Kingdom Animalia. Limitations: Did not distinguish between prokaryotes vs eukaryotes, unicellular vs multicellular, or photosynthetic (Green Algae) vs non-photosynthetic (Fungi) organisms.
- R.H. Whittaker (1969 - Five Kingdom System): Proposed Monera, Protista, Fungi, Plantae, and Animalia.
| Character | Monera | Protista | Fungi | Plantae | Animalia |
|---|---|---|---|---|---|
| Cell Type | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | Eukaryotic |
| Cell Wall | Non-cellulosic (Peptidoglycan) | Present in some (Silica/Cellulose) | Present (Chitin) | Present (Cellulose) | Absent |
| Nuclear Membrane | Absent | Present | Present | Present | Present |
| Body Organisation | Cellular | Cellular | Multicellular / Loose Tissue | Tissue / Organ | Tissue / Organ / System |
| Nutrition | Autotrophic & Heterotrophic | Autotrophic & Heterotrophic | Heterotrophic (Saprophytic/Parasitic) | Autotrophic (Photosynthetic) | Heterotrophic (Holozoic/Saprophytic) |
- Monera: E. coli, Anabaena, Nostoc, Mycoplasma pneumoniae
- Protista: Amoeba, Paramecium, Diatoms, Euglena, Plasmodium
- Fungi: Rhizopus (Bread Mould), Yeast (Saccharomyces), Agaricus (Mushroom), Penicillium
- \[Three-Domain System (Carl Woese): Domain Archaea\]\[Domain Bacteria\]\[Domain Eukarya (based on 16S rRNA gene sequences)\]
- \[Chitin = Nitrogen-containing polysaccharide polymer composing fungal cell walls\]
Kingdom Monera: Archaebacteria, Eubacteria & Mycoplasma
Fig 2.2 — High-Resolution Educational Poster: Monera Bacteria, Protista, Fungi Classes & Virus Structures
Kingdom Monera Characteristics
Core Monera Facts: Bacteria are the sole members of Kingdom Monera. Prokaryotic, unicellular, with non-cellulosic peptidoglycan cell walls. Mycoplasma lack a cell wall entirely and are the smallest living cells (0.3 μm).
1. Four Basic Shapes of Bacteria:
- Coccus (plural: Cocci): Spherical shape (e.g., Streptococcus).
- Bacillus (plural: Bacilli): Rod-shaped (e.g., Lactobacillus, E. coli).
- Vibrio (plural: Vibrios): Comma-shaped (e.g., Vibrio cholerae).
- Spirillum (plural: Spirilla): Spiral-shaped with flagella (e.g., Spirillum volutans).
2. Archaebacteria (Extreme Environment Bacteria):
Special cell wall structure (branched chain lipids) allows them to survive extreme harsh habitats:
- Halophiles: Live in extreme salty areas (e.g., Halobacterium).
- Thermoacidophiles: Live in hot sulphur springs (pH ~2, Temp ~80°C; e.g., Thermoplasma).
- Methanogens: Live in marshy areas and gut of ruminant animals (cows, buffaloes). Produce methane gas (biogas) from animal dung (e.g., Methanobacterium).
3. Eubacteria ('True Bacteria'):
- Possess a rigid cell wall and if motile, a flagellum.
- Cyanobacteria (Blue-Green Algae): Unicellular, colonial or filamentous, freshwater/marine or terrestrial. Photosynthetic autotrophs possessing chlorophyll 'a'. Filamentous forms (Nostoc and Anabaena) have specialized nitrogen-fixing cells called Heterocysts.
- Chemosynthetic Autotrophs: Oxidise inorganic substances (nitrates, nitrites, ammonia) to release energy for ATP production. Play a great role in recycling nitrogen, phosphorus, iron, and sulphur.
4. Mycoplasma (PPLO - Pleuropneumonia Like Organisms):
Organisms that completely lack a cell wall. Smallest known living cells (0.3 μm in length). Can survive without oxygen. Many are pathogenic in animals and plants.
- Heterocyst: Specialized thick-walled cell in Nostoc and Anabaena for nitrogen fixation.
- Mycoplasma: Smallest cell (0.3 μm), lacks cell wall, resistant to penicillin.
- Methanogens: Produce biogas (CH₄) in cattle rumen.
- \[N2 Fixation Equation: N₂ + 8e⁻ + 8H⁺ + 16 ATP → 2 NH₃ + H₂ + 16 ADP + 16 Pi (via Nitrogenase enzyme in Heterocysts)\]
Kingdom Fungi: Classes, Spores & Lichens
Fig 2.2 — High-Resolution Educational Poster: Monera Bacteria, Protista, Fungi Classes & Virus Structures
Kingdom Fungi & Fungal Classes
Fungi Key Features: Achlorophyllous, heterotrophic eukaryotic organisms. Cell wall made of Chitin. Body consists of long, slender thread-like structures called Hyphae (network of hyphae = Mycelium).
4 Main Classes of Fungi:
| Class | Mycelium | Asexual Spores | Sexual Spores | NCERT Examples |
|---|---|---|---|---|
| Phycomycetes | Aseptate & Coenocytic | Zoospores / Aplanospores | Zygospores | Mucor, Rhizopus (Bread mould), Albugo (Mustard parasite) |
| Ascomycetes (Sac Fungi) | Septate & Branched | Conidia (Exogenous) | Ascospores (Endogenous in Asci) | Aspergillus, Claviceps, Neurospora, Yeast (Unicellular) |
| Basidiomycetes (Club Fungi) | Septate & Branched | Absent generally | Basidiospores (Exogenous on Basidium) | Agaricus (Mushroom), Ustilago (Smut), Puccinia (Rust fungus) |
| Deuteromycetes (Imperfect Fungi) | Septate & Branched | Conidia | Absent (Sexual stage unknown) | Alternaria, Colletotrichum, Trichoderma |
- Neurospora is extensively used in biochemical and genetic work.
- Morels and Truffles belong to Ascomycetes and are edible delicacies.
- Lichens: Phycobiont (Algae) + Mycobiont (Fungi). Pollution indicators for SO₂.
- \[Plasmogamy → Karyogamy → Meiosis in zygote → Haploid spores\]
- \[Dikaryon stage (n + n): Two nuclei per cell in Ascomycetes and Basidiomycetes\]
Viruses, Viroids, Prions & Lichens
Fig 2.2 — High-Resolution Educational Poster: Monera Bacteria, Protista, Fungi Classes & Virus Structures
Viruses, Viroids & Prions
NCERT Discovery Milestones: Pasteur/Dmitri Ivanowsky (1892) discovered Virus. M.W. Beijerinek (1898) called it Contagium vivum fluidum (infectious living fluid). W.M. Stanley (1935) crystallized TMV. T.O. Diener (1971) discovered Viroids.
1. Viruses: Non-cellular organisms characterized by having an inert crystalline structure outside the living cell. Obligate intracellular parasites.
- Genetic Material: Contain either RNA or DNA (never both). Plant viruses usually have single-stranded RNA (ssRNA). Animal viruses have ssRNA, dsRNA, or double-stranded DNA (dsDNA). Bacteriophages usually have dsDNA.
- Protein Coat (Capsid): Made of small subunits called Capsomeres.
2. Viroids: Discovered by T.O. Diener in 1971 as a new infectious agent smaller than viruses. Causes Potato Spindle Tuber Disease (PSTD). Consists of free single-stranded RNA; lacks a protein coat.
3. Prions: Abnormally folded protein particles transmitting neurological diseases (BSE / Mad Cow Disease in cattle & Cr-Jacob disease CJD in humans).
- Contagium vivum fluidum: Beijerinek (1898)
- Viroid: Potato Spindle Tuber Disease (PSTD)
- Prion: BSE (Mad Cow Disease) and CJD
- \[Virus = Nucleic Acid (ssRNA / dsRNA / dsDNA) + Capsid\]
- \[Viroid = Free ssRNA without Capsid (T.O\]\[Diener 1971)\]
Related Laws & Principles
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