Biological Classification
'Classification is the arrangement of organisms into groups based on their similarities.' — Taxonomy
1. Chapter Overview
Building on the five-kingdom framework, this chapter DIVES DEEP into each kingdom — their CHARACTERISTIC FEATURES, CLASSIFICATION within each kingdom, and ECONOMIC IMPORTANCE. Special attention is given to KINGDOM MONERA (bacteria), FUNGI (with their unique life cycles), and VIRUSES (which straddle the living/non-living boundary). The chapter also covers VIROIDS, PRIONS, and LICHENS.
2. Kingdom Monera
Characteristics
- PROKARYOTIC (no membrane-bound organelles)
- Cell wall present (peptidoglycan)
- Naked DNA (circular)
- Ribosomes: 70S
- Reproduction: Asexual (binary fission)
- Flagella if present: SINGLE filament
Classification of Bacteria
| Basis | Type | Features |
|---|---|---|
| Shape | Coccus (spherical) | Cocci in chains/clusters |
| Bacillus (rod) | Single or chains | |
| Spirillum (spiral) | Corkscrew shape | |
| Vibrio (comma) | Curved rod | |
| Cell wall (Gram stain) | Gram + | Thick peptidoglycan, PURPLE stain |
| Gram - | Thin peptidoglycan + outer membrane, PINK stain | |
| Nutrition | Autotrophic | Photosynthetic (cyanobacteria or blue-green algae) |
| Chemosynthetic | Energy from inorganic chemicals (Nitrosomonas) | |
| Heterotrophic | Saprophytic, parasitic, symbiotic | |
| Respiration | Aerobic | Require O₂ |
| Anaerobic | Do NOT require O₂ |
Archaebacteria
- Ancient bacteria thriving in EXTREME environments
- Halophiles: Salt-loving (Great Salt Lake)
- Thermoacidophiles: Hot, acidic springs
- Methanogens: Produce methane, found in marshy areas and ruminant guts
Cyanobacteria (Blue-Green Algae)
- Photosynthetic autotrophs with CHLOROPHYLL a
- Fix atmospheric N₂ (heterocysts in Nostoc, Anabaena)
- Form BLOOMS in polluted water bodies
Mycoplasma
- SMALLEST living cells (0.1-0.3 μm)
- NO cell wall (therefore NOT affected by penicillin)
- Can survive WITHOUT O₂
3. Kingdom Protista
Characteristics
- EUKARYOTIC, UNICELLULAR (or simple multicellular)
- Diverse nutrition — photosynthetic, holozoic, saprophytic
- Link between Monera and higher kingdoms
Major Groups
| Group | Example | Features |
|---|---|---|
| Chrysophytes | Diatoms, Desmids | Golden-yellow colour, SILICA cell wall. Diatomaceous earth |
| Dinoflagellates | Gonyaulax | Two flagella, RED TIDE, cellulose plates |
| Euglenoids | Euglena | Photosynthetic (light) + heterotrophic (dark) — MIXOTROPHIC. Pellicle, NOT cell wall |
| Slime Moulds | Physarum | Saprophytic, forms PLASMODIUM (multinucleate mass), spore formation |
| Protozoans | Amoeba, Paramecium, Plasmodium | Heterotrophic. Amoeboid, Ciliated, Flagellated, Sporozoans |
4. Kingdom Fungi
Characteristics
- EUKARYOTIC, HETEROTROPHIC (saprophytic/parasitic)
- Cell wall: CHITIN (NOT cellulose like plants)
- Body: THALLUS (mycelium — network of hyphae)
- Reproduction: Spores (conidia, sporangiospores)
Classification
| Class | Hyphae | Reproduction | Examples |
|---|---|---|---|
| Phycomycetes | Aseptate (coenocytic) | Asexual (sporangiospores), Sexual (zygospores) | Rhizopus (bread mould), Mucor |
| Ascomycetes | Septate | Asexual (conidia), Sexual (ascospores in ASCI) | Penicillium, Aspergillus, Yeast |
| Basidiomycetes | Septate | Sexual (basidiospores on BASIDIA) | Mushroom, Bracket fungi, Rusts |
| Deuteromycetes | Septate | ONLY asexual known ('Imperfect fungi') | Alternaria, Colletotrichum |
Mycorrhiza
- SYMBIOTIC association between fungi and plant roots
- Ectomycorrhiza: Fungus outside roots
- Endomycorrhiza: Fungus INSIDE roots
5. Kingdom Plantae and Animalia
Plantae
- EUKARYOTIC, CELLULOSIC cell wall
- AUTOTROPHIC (photosynthetic)
- Storage: Starch
- Classification (Eichler): Cryptogams (Thallophyta, Bryophyta, Pteridophyta) and Phanerogams (Gymnosperms, Angiosperms)
Animalia
- EUKARYOTIC, NO cell wall
- HETEROTROPHIC (holozoic)
- Storage: Glycogen
- Classified based on body organisation, symmetry, coelom
6. Viruses, Viroids, and Lichens
Viruses
- Obligate INTRACELLULAR parasites — can't reproduce outside host
- Structure: Protein coat (capsid) + Nucleic acid (DNA or RNA, never both)
- LIVING inside host (reproduce, mutate); NON-LIVING outside (crystallise, no metabolism)
- Tobacco Mosaic Virus (TMV): First virus discovered, RNA virus
- Bacteriophage: Virus that infects BACTERIA
Viroids
- Found by T.O. Diener (1971)
- NAKED RNA molecules (NO protein coat)
- Cause potato spindle tuber disease
Prions
- Infectious PROTEIN particles (NO nucleic acid)
- Cause MAD COW disease (BSE), Creutzfeldt-Jakob disease
Lichens
- SYMBIOTIC association: FUNGUS (mycobiont) + ALGA (phycobiont)
- Fungus provides ABSORPTION; Alga provides FOOD
- Indicators of AIR POLLUTION (die in polluted air)
- Types: Crustose, Foliose, Fruticose
7. Common Mistakes
- Monera ≠ single group: Two distinct groups — Archaebacteria and Eubacteria
- Fungi are NOT plants: They have CHITIN cell wall (not cellulose) and are heterotrophic
- Viruses are NOT classified under any kingdom: They are acellular and are studied separately
- Euglena is NOT a plant: It is a PROTOZOAN (phylum Euglenozoa) in Kingdom Protista
- Diatomaceous earth ≠ sand: It is fossilised diatom cell walls (silica), used in filtration
8. CBSE Exam Focus
- Five-kingdom classification — basis and features (5-mark)
- Bacteria — Gram staining, shapes, nutrition (3-mark)
- Fungi — classification and economic importance (5-mark)
- Viruses — structure, replication (3-mark)
- Lichens — symbiosis, importance (3-mark)
9. Key Points
- Monera = Prokaryotic (no nucleus)
- Protista = Unicellular Eukaryotes
- Fungi = Chitin cell wall, heterotrophic
- Plantae = Cellulose wall, autotrophic
- Animalia = No cell wall, heterotrophic
- Viruses = Obligate parasites, protein + nucleic acid
10. Self-Test (5+ Q&A)
Q1: What is the basis of five-kingdom classification by Whittaker? A: Cell structure (prokaryotic/eukaryotic), body organisation (unicellular/multicellular), mode of nutrition (autotrophic/heterotrophic), reproduction, and phylogenetic relationships.
Q2: Differentiate between Gram-positive and Gram-negative bacteria. A: Gram+ bacteria have thick peptidoglycan wall (stain PURPLE). Gram- bacteria have thin peptidoglycan + outer membrane (stain PINK).
Q3: Why are viruses considered both living and non-living? A: NON-LIVING outside host (crystallise, no metabolism). LIVING inside host (reproduce, mutate, evolve).
Q4: What are lichens? Why are they called indicators of air pollution? A: Symbiotic association of fungi + algae. They absorb water and nutrients from air, so they are VERY SENSITIVE to air pollutants (especially SO₂) and die in polluted environments.
Q5: Name the classes of fungi with one example each. A: Phycomycetes (Rhizopus), Ascomycetes (Penicillium), Basidiomycetes (Agaricus — mushroom), Deuteromycetes (Alternaria).
11. Conclusion
Biological classification ORGANISES the immense diversity of life into MANAGEABLE groups. The five-kingdom system (Monera, Protista, Fungi, Plantae, Animalia) is based on fundamental differences in cell structure and nutrition mode. Bacteria are PROKARYOTIC workhorses of the biosphere. Fungi are DECOMPOSERS with unique chitin cell walls. Viruses challenge our definition of 'life'. Understanding classification is ESSENTIAL for studying biodiversity, evolution, and ecology.
