Learning Objectives
- Understand different systems of classification
- Learn the Five Kingdom Classification by R.H. Whittaker
- Study the characteristic features of Monera, Protista, Fungi, Plantae, and Animalia
- Understand viruses, viroids, prions, and lichens
Key Concepts
Classification Systems
Two Kingdom Classification (Linnaeus): Plantae and Animalia. Drawback: Did not distinguish between prokaryotes and eukaryotes, unicellular and multicellular organisms.
Five Kingdom Classification (R.H. Whittaker, 1969): Based on cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships. The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia.
Kingdom Monera
Prokaryotic organisms lacking a true nucleus and membrane-bound organelles. Includes bacteria and cyanobacteria (blue-green algae). Cell wall present (except Mycoplasma). Nutrition: autotrophic (photosynthetic or chemosynthetic) or heterotrophic (saprophytic or parasitic).
Bacterial shapes: Coccus (spherical), Bacillus (rod-shaped), Vibrio (comma-shaped), Spirillum (spiral). Archaebacteria: Live in extreme habitats — halophiles (salty), thermoacidophiles (hot springs), methanogens (marshy areas, gut of ruminants). Methanogens produce biogas (methane).
Eubacteria: True bacteria. Cyanobacteria are photosynthetic autotrophs with chlorophyll a, also called blue-green algae. Nostoc and Anabaena can fix atmospheric nitrogen. Mycoplasma: Smallest living organisms, lack cell wall, pleomorphic, can survive without oxygen, cause diseases like mycoplasmal pneumonia.
Kingdom Protista
Eukaryotic, mostly unicellular organisms. Movement by cilia, flagella, or pseudopodia. Includes: Chrysophytes (diatoms, golden algae — diatomaceous earth used in filtration), Dinoflagellates (mostly marine, cause red tides), Euglenoids (freshwater, mixotrophic, protein-rich pellicle), Slime Moulds (saprophytic, form plasmodium during favorable conditions), Protozoans (heterotrophs — Amoeba, Paramecium, Plasmodium, Trypanosoma).
Kingdom Fungi
Eukaryotic, heterotrophic organisms with a chitinous cell wall. Body is made of thread-like hyphae, forming a network called mycelium. Nutrition is saprophytic, parasitic, or symbiotic (lichens = algae + fungi; mycorrhiza = fungi + plant roots).
Phycomycetes: Algal fungi, aseptate coenocytic mycelium. Example: Mucor, Rhizopus, Albugo. Ascomycetes: Sac fungi, produce ascospores in asci. Example: Aspergillus, Neurospora, Saccharomyces (yeast), morels, truffles. Basidiomycetes: Club fungi, produce basidiospores on basidia. Example: Agaricus (mushroom), puffballs, bracket fungi. Deuteromycetes: Imperfect fungi, only asexual reproduction known. Example: Alternaria, Colletotrichum, Trichoderma.
Viruses, Viroids, Prions, and Lichens
Viruses: Non-cellular, obligate intracellular parasites. Discovered by D.J. Ivanowsky (TMV). Crystallized by W.M. Stanley. Consist of protein coat (capsid) and nucleic acid core (either DNA or RNA, never both). Bacteriophage infects bacteria.
Viroids: Discovered by T.O. Diener. Free RNA without protein coat. Cause potato spindle tuber disease.
Prions: Abnormal proteins that cause infectious neurological diseases like mad cow disease (BSE) and Creutzfeldt-Jakob disease (CJD).
Lichens: Symbiotic association between algae (phycobiont) and fungi (mycobiont). They are pollution indicators as they do not grow in polluted areas.
Summary
Whittaker proposed the Five Kingdom Classification based on cell structure, nutrition, and reproduction. Monera includes prokaryotes (bacteria). Protista includes unicellular eukaryotes. Fungi are heterotrophic eukaryotes with chitinous cell walls. Viruses are non-cellular entities with DNA or RNA. Viroids are free RNA molecules. Prions are infectious proteins. Lichens indicate pollution-free environments.
Important Terms
- Archaebacteria: Ancient bacteria living in extreme environments
- Cyanobacteria: Photosynthetic prokaryotes, also called blue-green algae
- Mycoplasma: Smallest living organisms without cell wall
- Diatomaceous earth: Cell wall deposits of diatoms, used in filtration and polishing
- Mycelium: Network of fungal hyphae
- Lichen: Symbiotic association of algae and fungi; pollution indicators
- Capsid: Protein coat of a virus made of capsomeres
- Viroid: Infectious RNA particle without protein coat
Quick Revision
- Five Kingdom Classification by Whittaker (1969): Monera, Protista, Fungi, Plantae, Animalia
- Monera = prokaryotes; Protista = unicellular eukaryotes
- Fungi cell wall = chitin; nutrition = saprophytic/parasitic/symbiotic
- Virus = protein + nucleic acid (DNA or RNA); discovered by Ivanowsky
- Viroids = free RNA (Diener); Prions = infectious proteins
- Lichens = algae + fungi = pollution indicators
- Methanogens produce methane (biogas), found in gut of cattle
- Diatoms have siliceous cell walls (frustules)