Biological Classification
1. History of Biological Classification & Kingdom Monera
A. Evolution of Classification Systems
- Aristotle (Earliest Scientific Basis): Divided plants into Herbs, Shrubs, Trees; Animals into Enaima (with RBCs) and Anaima (without RBCs).
- 2-Kingdom System (Linnaeus): Plantae & Animalia.
• Limitation: Placed Bacteria, Fungi, Algae together; failed to distinguish Prokaryotes vs. Eukaryotes, Unicellular vs. Multicellular, and Photosynthetic vs. Non-photosynthetic (Fungi cell wall made of Chitin vs. Plant cell wall made of Cellulose).
- 3-Kingdom System (Ernst Haeckel): Introduced Kingdom Protista for unicellular organisms.
- 4-Kingdom System (Copeland): Introduced Kingdom Monera for prokaryotes.
- 5-Kingdom System (R.H. Whittaker – 1969): Criteria based on Cell Structure, Body Organisation, Mode of Nutrition, Reproduction, and Phylogenetic Relationships (Monera, Protista, Fungi, Plantae, Animalia).
- 3-Domain System (Carl Woese): Based on 16S rRNA gene sequencing. Divided life into Archaea, Bacteria (Prokaryota), and Eukarya.
B. Kingdom Monera – Archaebacteria vs. Eubacteria
- Bacteria are the sole members of Monera; most abundant micro-organisms. Prokaryotic.
- Archaebacteria (Extremophiles): Survive extreme environments due to branched-chain lipid monolayer cell membranes and pseudo-murein wall.
• Halophiles: Extreme salty conditions.
• Thermoacidophiles: Hot sulfur springs ($80^\circ\text{C}$, acidic pH).
• Methanogens: Marshy areas and gut of ruminant animals (produces Biogas / $\text{CH}_4$).
2. Cyanobacteria, Mycoplasma & Bacterial Nutrition
A. Cyanobacteria (Blue-Green Algae) & Mycoplasma
- BGA / Cyanobacteria: Non-motile, unicellular/colonial/filamentous with rigid cell wall surrounded by gelatinous/mucilaginous sheath.
• Perform oxygenic photosynthesis using Chlorophyll-a, c-Phycocyanin (blue), and c-Phycoerythrin (red). Uses $\text{H}_2\text{O}$ as electron donor to release $\text{O}_2$.
• Heterocysts: Specialized large, thick-walled anaerobic cells for atmospheric Nitrogen fixation ($\text{N}_2 \to \text{NH}_3$) e.g., Anabaena, Nostoc.
• Symbiosis: Anabaena $+$ Azolla (water fern).
- Mycoplasma (PPLO): Smallest living cell ($0.1\text{–}0.3\ \mu\text{m}$); completely lacks cell wall (resistant to penicillin, insensitive to cell-wall targeting antibiotics). Can survive anaerobically. “Jokers of Plant Kingdom”; pathogenic in animals and plants.
B. Nutrition & Reproduction in Bacteria
| Nutritional Type | Mechanism & Electron / Energy Source | Examples |
|---|---|---|
| Photoautotrophic | Oxygenic (BGA uses $\text{H}_2\text{O}$) vs. Anoxygenic (Purple/Green sulfur bacteria use $\text{H}_2\text{S}$ as $\mathbf{e^-}$ donor). | Chromatium, Chlorobium, Anabaena. |
| Chemoautotrophic | Oxidizes inorganic substances ($\text{NH}_3, \text{NO}_2^-, \text{H}_2\text{S}$) to generate ATP. Plays major role in nutrient recycling. | Nitrifying bacteria (Nitrosomonas, Nitrobacter). |
| Heterotrophic | Majority of bacteria. Saprophytes (decomposers) or Parasites. • Symbionts: Rhizobium (in legume root nodules), Frankia (in non-legumes). | Pathogens causing Cholera, Typhoid, Tetanus, Citrus Canker. |
- Reproduction: Primarily asexual via Binary Fission (favourable conditions) or Endospore Formation (unfavourable conditions). Sexual recombination occurs via primitive gene transfer: Transformation, Transduction, Conjugation.
3. Kingdom Protista (Unicellular Eukaryotes)
A. General Characteristics & Chrysophytes
- All single-celled eukaryotes. Forms a link between Monera and complex multicellular kingdoms (Fungi, Plantae, Animalia).
- 1. Chrysophytes (Diatoms & Golden Algae/Desmids): Photosynthetic, microscopic plankton found in fresh and marine water.
• Cell wall forms two thin overlapping shells fitting together like a soap box impregnated with indestructible Silica.
• Accumulation of cell wall deposits over millions of years forms Diatomaceous Earth (used in polishing, filtration of oils & syrups). Diatoms are the chief producers in the oceans.
B. Dinoflagellates, Euglenoids & Slime Moulds
- 2. Dinoflagellates: Mostly marine & photosynthetic. Cells have stiff cellulosic plates. Possess 2 flagella (one longitudinal, one transverse in a furrow between wall plates).
• Rapid multiplication of red dinoflagellates (e.g., Gonyaulax) causes Red Tides and releases toxins (saxitoxin) killing marine aquatic animals/fishes. Bioluminescent species: Noctiluca.
- 3. Euglenoids (e.g., Euglena): Stagnant freshwater. Lack cell wall; instead, possess a protein-rich flexible outer layer called Pellicle.
• Possess 2 flagella (1 short, 1 long). Show Mixotrophic Nutrition (photosynthetic in sunlight, predatory heterotroph in darkness).
- 4. Slime Moulds: Saprophytic protists.
• Favourable Conditions: Form an aggregation called Plasmodium which moves along decaying twigs feeding on organic matter.
• Unfavourable Conditions: Plasmodium differentiates into fruiting bodies bearing spores at tips. Spores possess true resistant cell walls and disperse via air currents.
4. Protozoans & Kingdom Fungi Overview
A. Protozoan Groups (Heterotrophic Protists)
| Group | Locomotory Organelle | Features & Key Examples |
|---|---|---|
| Amoeboid | Pseudopodia (“false feet”) | Freshwater, sea water or moist soil. Marine forms have silica shells. Ex: Amoeba (free-living), Entamoeba histolytica (parasite). |
| Flagellated | Flagella | Free-living or parasitic. Ex: Trypanosoma (causes Sleeping Sickness transmitted by tsetse fly). |
| Ciliated | Thousands of Cilia | Aquatic, actively moving with a cavity (gullet) opening to outside. Shows Nuclear Dimorphism (Macro & Micronucleus). Ex: Paramecium. |
| Sporozoans | ABSENT | Endoparasites with an infectious spore-like stage in life cycle. Ex: Plasmodium (Malarial parasite). |
B. Kingdom Fungi Structure & Spore Types
- Achlorophyllous, heterotrophic (saprophytic/parasitic) eukaryotes. Cell wall made of Chitin and glucans; reserve food is Glycogen and oil.
- Structure: Body consists of long, slender thread-like filaments called Hyphae. Network of hyphae is Mycelium.
• Coenocytic / Aseptate: Continuous tubes filled with multinucleated cytoplasm (Phycomycetes).
• Septate: Cross-walls present in hyphae (Ascomycetes, Basidiomycetes, Deuteromycetes).
• Unicellular exception: Yeast (Saccharomyces).
- Asexual Spore Types:
• Zoospores: Motile, flagellated, endogenous (inside zoosporangium).
• Aplanospores / Sporangiospores: Non-motile, thin-walled, endogenous.
• Conidia: Non-motile, exogenous (formed at tips of specialized hyphae called conidiophores e.g., Penicillium, Aspergillus).
5. Fungi Life Cycle Steps & Comparative Table
A. Sexual Reproduction Steps & Dikaryon Phase
- 1. Plasmogamy: Fusion of protoplasms between two motile or non-motile gametes.
- 2. Karyogamy: Fusion of two haploid nuclei.
- 3. Meiosis: Reductional division in zygote ($2n$) resulting in haploid spores ($n$).
B. Master Comparative Table of Fungi Classes
| Feature | Phycomycetes (Algal Fungi) | Ascomycetes (Sac Fungi) | Basidiomycetes (Club Fungi) | Deuteromycetes (Imperfect Fungi) |
|---|---|---|---|---|
| Habitat & Mycelium | Aquatic / decaying wood in damp places. Aseptate & Coenocytic. | Saprophytic, decomposers, coprophilous (growing on dung). Septate & branched. | Grow in soil, logs, tree stumps, plant parasites. Septate & branched. | Decomposers of litter, mineral recyclers. Septate & branched. |
| Asexual Spores | Zoospores (motile) or Aplanospores (non-motile); Endogenous. | Conidia produced exogenously on conidiophores. | Asexual spores generally NOT FOUND; vegetative by fragmentation. | Reproduce only by asexual spores called Conidia. |
| Sexual Spores & Fruiting Body | Zygospore (from gametangial fusion). Fruiting body absent. | Ascospores produced endogenously inside sac-like Ascus (plural: Anci) in Ascocarp. | Sex organs absent! Somatogamy forms dikaryon. Basidiospores produced exogenously on Basidium in Basidiocarp. | SEXUAL STAGE ABSENT / UNKNOWN (Hence called ‘Imperfect’). When sexual stage discovered, moved to Ascomycetes/Basidiomycetes. |
| Examples | Mucor, Rhizopus (bread mould), Albugo (parasitic on mustard). | Yeast, Penicillium, Aspergillus, Claviceps, Neurospora (used in genetics), Morels & Truffles (edible). | Agaricus (Mushroom), Ustilago (Smut), Puccinia (Rust fungus), Bracket fungi, Puffballs. | Alternaria, Colletotrichum, Trichoderma. |
6. Acellular Entities: Viruses, Viroids, Prions & Lichens
- Viruses (Non-cellular): Not included in Whittaker’s 5-Kingdom classification. Inert crystalline structure outside living cell; obligate intracellular parasites.
• D.J. Ivanowsky (1892): Discovered Tobacco Mosaic Virus (TMV); smaller than bacteria as they passed through bacteria-proof filters.
• M.W. Beijerinck (1898): Demonstrated infected plant sap infects healthy plants $\to$ Named fluid “Contagium vivum fluidum” (infectious living fluid).
• W.M. Stanley (1935): Showed viruses could be crystallized (crystals consist largely of proteins).
• Genetic Composition: Nucleoprotein entity containing either RNA or DNA (never both!).
↳ Plant viruses: Mostly ssRNA.
↳ Animal viruses: ssRNA, dsRNA, or dsDNA.
↳ Bacterial viruses (Bacteriophages): Usually double-stranded DNA (dsDNA).
• Capsid: Protein coat made of small subunit capsomeres protecting nucleic acid.
- Viroids (T.O. Diener – 1971): Infectious agent smaller than viruses. Causes Potato Spindle Tuber Disease. Consists of free, low molecular weight RNA lacking protein coat.
- Prions: Abnormally folded infectious proteinaceous agents (similar in size to viruses). Cause Bovine Spongiform Encephalopathy (BSE / Mad Cow Disease) in cattle and Cr-Jacob Disease (CJD) in humans.
- Lichens: Symbiotic mutualistic association between Algae (Phycobiont – autotrophic, prepares food) and Fungi (Mycobiont – heterotrophic, provides shelter and absorbs water/minerals).
• Lichens do not grow in polluted areas $\to$ Act as excellent $\text{SO}_2$ Pollution Indicators!
