🔬 Biological Classification

1. Systems of Classification

Initially, Aristotle classified organisms into plants and animals. Later, Linnaeus gave the Two-Kingdom system (Plantae and Animalia). However, this did not distinguish between eukaryotes/prokaryotes or unicellular/multicellular.

🖐️ Five Kingdom Classification

Proposed by R.H. Whittaker (1969). The kingdoms are:

1. Monera (Prokaryotes)

2. Protista (Unicellular Eukaryotes)

3. Fungi (Multicellular, Heterotrophic, Chitin wall)

4. Plantae (Multicellular, Autotrophic)

5. Animalia (Multicellular, Heterotrophic, No cell wall)

2. Kingdom Monera

Comprises all bacteria. They are the most abundant micro-organisms. Based on shape: Coccus (spherical), Bacillus (rod), Vibrio (comma), Spirillum (spiral).

Archaebacteria: Live in extreme habitats (halophiles, thermoacidophiles, methanogens).
Eubacteria: 'True bacteria' with a rigid cell wall. Includes Cyanobacteria (blue-green algae) and mycoplasma (lacks a cell wall).

3. Kingdom Protista

Single-celled eukaryotes. Primarily aquatic. Includes:

Chrysophytes (Diatoms and golden algae)
Dinoflagellates (Cause 'red tides')
Euglenoids (Mixotrophic nutrition)
Slime Moulds (Saprophytic)
Protozoans (Amoeboid, Flagellated, Ciliated, Sporozoans)

4. Kingdom Fungi

Heterotrophic organisms. Network of hyphae is called mycelium. Cell wall made of chitin. Divided into: Phycomycetes, Ascomycetes (sac-fungi), Basidiomycetes (club-fungi), and Deuteromycetes (imperfect fungi).

5. Viruses, Viroids, and Lichens

These are acellular and not included in the five-kingdom system.

Viruses

Consist of a protein coat (capsid) and genetic material (DNA or RNA, never both). They are obligate intracellular parasites.

Lichens: Symbiotic association between algae (phycobiont) and fungi (mycobiont). Excellent pollution indicators.