Early to Modern Classification
Early classifications were non-scientific, based purely on human needs for food, shelter, and clothing.
First Scientific Classification: Aristotle
Aristotle, the Father of Biology and Zoology (Teacher of Alexander the Great), used 1-2 morphological characters to classify organisms. He authored Historia Animalium and Historia Plantarum.
- Plants: Classified into Herbs, Shrubs, and Trees.
- Animals: Classified into Enaima (having RBC - vertebrates) and Anaima (RBC absent - Invertebrates).
Two Kingdom System: Carolus Linnaeus
Divided living organisms into Plantae (have cell wall, autotrophic) and Animalia (do not have cell wall, heterotrophic). Flaw: Linnaeus wrongly placed Fungi (which have a cell wall but are heterotrophs) with Plantae.
Three Kingdom System: Ernst Haeckel
Created the kingdom Protista, placing all unicellular organisms separately from Plantae and Animalia.
Four Kingdom System: Herbert Copeland
Separated unicellular prokaryotes into a new kingdom: Monera. Protista was left with unicellular eukaryotes.
Five Kingdom System: R.H. Whittaker (1969)
This is the most accepted classification system. He separated Fungi based on their heterotrophic (saprophytic) mode of nutrition and loose tissue (mycelium/hyphae) with chitinous cell walls.
Main Criteria chosen by Whittaker:
- Mode of Nutrition (Primary Criteria)
- Cellular Structure Complexity (Prokaryotic vs Eukaryotic)
- Body Organization (Cellular, Tissue, Organ, Organ System)
- Phylogenetic Relationship (Evolutionary history)
- Reproduction
- Ecological Role (Producer, Consumer, Decomposer)
| Kingdom |
Cell Type |
Key Features |
| Monera |
Unicellular Prokaryotes |
Phototrophs, Chemotrophs, Heterotrophs |
| Protista |
Unicellular Eukaryotes |
Autotrophs, Heterotrophs, Mixotrophic |
| Fungi |
Multicellular Eukaryotes |
Saprophytic, Loose tissue (Mycelium), Chitin cell wall |
| Plantae |
Multicellular Eukaryotes |
Autotrophic |
| Animalia |
Multicellular Eukaryotes |
Heterotrophic, Holozoic (Ingestive) nutrition |
Three Domain System: Carl Woese
Also known as the 6 Kingdom classification. Based on 16S rRNA (a "Noble RNA" because it is highly conserved, doesn't evolve rapidly, and is present in all prokaryotes). Variations in its sequence determine evolutionary relationships.
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Kingdom Monera: General Overview
Kingdom Monera consists entirely of unicellular prokaryotes. They exhibit an extraordinary level of diversity in size, shape, habitat, flagellar arrangement, and metabolic activity.
NCERT Excerpt
Statement: Bacteria are Simple in Structure but Complex in Behaviour. They show the most extensive Metabolic diversity.
Habitat: Found Everywhere ("Ubiquitous"). Hundreds of Bacteria are present in a Handful of Soil.
1. Diversity in Size & Shape
Typical bacteria range from 1-2 Ξm. They are grouped into four shapes:
- Bacillus: Rod-shaped. Can form endospores.
- Coccus: Spherical. Forms groups: Streptococcus (chain), Staphylococcus (bunch). Note: Coccus are generally non-motile.
- Spirillum: Spiral-shaped.
- Vibrio: Comma-shaped.
2. Diversity in Habitat
Bacteria are ubiquitous. They thrive in extreme conditions such as Hot Springs, Deep Oceans, Deserts, and Snow. They are not found in the blood of a healthy person.
3. Diversity in Flagellar Arrangement
- Monotrichous: Single flagellum at one end.
- Amphitrichous: Single flagellum at both ends.
- Lophotrichous: Tuft of flagella at one end.
- Amphilophotrichous: Tuft of flagella at both ends.
- Peritrichous: Flagella distributed all over the body surface.
Metabolic Diversity & Nutrition
1. Autotrophs
- Phototrophs: Synthesize food using energy from sunlight.
- Photolithotrophs: Use inorganic sources for electron/H+ directly from nature.
- Photoorganotrophs: Use organic sources for electron/H+.
- Chemotrophs: Synthesize food using energy from chemicals.
- Chemolithotrophs: Inorganic chemicals.
- Chemoorganotrophs: Organic chemicals.
NCERT Excerpt
The vast majority of Bacteria are Heterotrophs and they are the "Most abundant in Nature". Majority of them are "Decomposers" which break down organic matter into inorganic matter.
Respiration & Oxygen Requirement
- Obligate Aerobes: Always require oxygen.
- Obligate Anaerobes: Do not survive in oxygen.
- Facultative Aerobes: Basically anaerobes, but may survive in aerobic conditions.
- Facultative Anaerobes: Basically aerobes, but can survive without oxygen.
Reproduction in Bacteria
1. Binary Fission
The most common method of bacterial reproduction.
2. Genetic Recombination
True sexual reproduction does not occur, but a sort of sexual reproduction exists through Genetic Recombination.
- Conjugation:
- F+ x F- : Transfer of F factor (plasmid) via a sex pilus. Known as Sexduction.
- Hfr x F- : High Frequency Recombination. Plasmid integrates with main DNA to form an Episome.
- Transformation: Transfer of transforming DNA elements from an S-III (smooth) strain to an R-II (rough) strain.
- Transduction: Genetic transfer mediated by a Bacteriophage. Fact: Bacteriophages were first discovered by Twort in the River Ganges.
Pathogenic Bacteria: Disease Generators
15 Human Bacterial Diseases
| Disease | Causative Bacterium |
|---|
| 1. Tuberculosis | Mycobacterium tuberculosis |
| 2. Cholera | Vibrio cholerae |
| 3. Typhoid | Salmonella typhi |
| 4. Pneumonia | Streptococcus pneumoniae |
| 5. Tetanus | Clostridium tetani |
| 6. Diphtheria | Corynebacterium diphtheriae |
| 7. Whooping Cough | Bordetella pertussis |
| 8. Anthrax | Bacillus anthracis |
| 9. Syphilis | Treponema pallidum |
| 10. Gonorrhoea | Neisseria gonorrhoeae |
| 11. Botulism | Clostridium botulinum |
| 12. Leprosy | Mycobacterium leprae |
| 13. E. coli Infection | Escherichia coli |
| 14. Dysentery | Shigella dysenteriae |
| 15. Wound Infection | Staphylococcus aureus |
5 Plant Bacterial Diseases
- Blight of Cotton: Xanthomonas axonopodis pv. malvacearum
- Citrus Canker: Xanthomonas citri subsp. citri
- Fire blight of Apple/Pear: Erwinia amylovora
- Crown Gall: Agrobacterium tumefaciens
- Tundu of Wheat: Clavibacter tritici
Nitrogen Cycle & Biological Nitrogen Fixation
Cycle Overview:
N2 â (Nitrogenase Enzyme) â Nitrogen Fixation â NH3 (Ammonia) â (Nitrosomonas) â NO2- (Nitrite) â (Nitrobacter) â NO3- (Nitrate) â Nitrification.
Plants absorb Nitrates â Consumed by animals â Death/Decay â Ammonification.
Nitrates back to N2 â Denitrification.
Biological Nitrogen Fixers
- Free-Living Nitrogen Fixers:
- Cyanobacteria: Nostoc, Anabaena, Oscillatoria, Aulosira
- Aerobic Bacteria: Azotobacter, Azospirillum, Beijerinckia
- Anaerobic Bacteria: Clostridium, Rhodospirillum
- Symbiotic Nitrogen Fixers:
- Leguminous Plants + Rhizobium
- Non-Leguminous Plants (Alnus, Casuarina) + Frankia
- Fern Azolla: Symbiosis with Anabaena.
- Coralloid Roots of Cycas: Symbiosis with Nostoc.
Special Monerans
1. Archaebacteria
More primitive than true bacteria, known for surviving in harsh, extreme habitats.
- Halophiles: Extreme salty areas.
- Thermoacidophiles: Hot springs (High temp & acidic pH).
- Methanogens: Marshy habitats, stomach of ruminants, paddy fields. Produce methane gas.
NCERT Excerpt
Their survival in extreme conditions is due to differences in structure compared to normal Bacteria:
- Cell wall made of pseudomurein.
- Cell membrane contains branched-chain alcohols instead of fatty acids, forming ether bonds (chemically more stable than ester bonds).
- Lipids show overlapping so the bilayer appears as a stable monolayer.
2. Cyanobacteria (Blue-Green Algae)
Unicellular prokaryotes. They are the first organisms to release O2 in the atmosphere because they possess Chlorophyll 'a' in both PS-I and PS-II.
- Morphology: Exist as filamentous forms or colonial forms.
- Heterocyst: Specialized, thick-walled cells present in the filament capable of atmospheric N2 fixation.
- Contains the Nitrogenase enzyme.
- PS-II is absent in heterocysts, meaning no O2 is released here, protecting the oxygen-sensitive Nitrogenase.
- PS-I is present, so they can perform photosynthesis.
3. Mycoplasma
The smallest living organisms known. They completely lack a cell wall.
- Pathogenic in plants and animals.
- Resistant to Penicillin: Penicillin works by inhibiting cell wall synthesis. Since Mycoplasma lack a cell wall, it has no effect on them.
- They are Facultative Anaerobes (may survive in the absence of oxygen).
- Colonies require sterols for growth and appear like a "Fried egg".
- Possess usual circular DNA.