Biological classification is the process of arranging organisms into groups based on similarities and differences. It helps in:
- Identifying organisms
- Understanding relationships
- Studying diversity efficiently
Early classification systems were artificial, but modern systems are based on evolutionary relationships.
Need for Classification
- Makes study of organisms easier
- Helps in identification
- Shows evolutionary relationships
- Organizes vast biodiversity
Two Kingdom Classification
Proposed by Carolus Linnaeus:
Kingdoms:
- Plantae
- Animalia
Limitations:
- No distinction between prokaryotes and eukaryotes
- No separation of unicellular and multicellular organisms
- Fungi placed with plants
- No place for microorganisms
Five Kingdom Classification
Proposed by R. H. Whittaker (1969).
Basis of Classification:
- Cell structure
- Body organization
- Mode of nutrition
- Reproduction
- Phylogenetic relationships
Five Kingdoms
- Monera
- Protista
- Fungi
- Plantae
- Animalia
Kingdom Monera
Characteristics:
- Prokaryotic organisms
- Unicellular
- No membrane-bound organelles
- Cell wall usually present
Types of Monerans
1. Bacteria
- Most abundant organisms
- Can be autotrophic or heterotrophic
Types based on shape:
- Cocci (spherical)
- Bacilli (rod-shaped)
- Spirilla (spiral)
- Vibrios (comma-shaped)
2. Cyanobacteria (Blue-green algae)
- Photosynthetic
- Fix atmospheric nitrogen
3. Mycoplasma
- Smallest living cells
- Lack cell wall
Kingdom Protista
Characteristics:
- Eukaryotic
- Mostly unicellular
- Aquatic
Groups of Protists
1. Chrysophytes
- Includes diatoms
- Silica cell wall
2. Dinoflagellates
- Two flagella
- Cause red tides
3. Euglenoids
- Mixotrophic (autotrophic + heterotrophic)
- No cell wall
4. Protozoans
Types:
- Amoeboids (Amoeba)
- Flagellates (Trypanosoma)
- Ciliates (Paramecium)
- Sporozoans (Plasmodium)
Kingdom Fungi
Characteristics:
- Eukaryotic
- Heterotrophic (saprophytic/parasitic)
- Cell wall made of chitin
Structure
- Body made of hyphae
- Network of hyphae = mycelium
Classification of Fungi
1. Phycomycetes
- Example: Rhizopus
2. Ascomycetes
- Sac fungi
- Example: Yeast
3. Basidiomycetes
- Club fungi
- Example: Mushroom
4. Deuteromycetes
- Imperfect fungi
- Example: Alternaria
Kingdom Plantae
Characteristics:
- Multicellular
- Autotrophic
- Cell wall made of cellulose
Classification:
- Algae
- Bryophytes
- Pteridophytes
- Gymnosperms
- Angiosperms
Kingdom Animalia
Characteristics:
- Multicellular
- Heterotrophic
- No cell wall
- Mostly motile
Viruses
Characteristics:
- Non-cellular
- Obligate parasites
- Can reproduce only inside host
Structure:
- Genetic material (DNA or RNA)
- Protein coat (capsid)
Viroids
- Small infectious RNA molecules
- No protein coat
Prions
- Infectious proteins
- Cause neurodegenerative diseases
Differences Between Five Kingdoms
| Feature | Monera | Protista | Fungi | Plantae | Animalia |
|---|---|---|---|---|---|
| Cell type | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | Eukaryotic |
| Organization | Unicellular | Mostly unicellular | Multicellular | Multicellular | Multicellular |
| Nutrition | Auto/hetero | Mixed | Heterotrophic | Autotrophic | Heterotrophic |
Important NEET & CBSE Points
- Five kingdom classification by Whittaker (1969)
- Monera = prokaryotes
- Protista = unicellular eukaryotes
- Fungi cell wall = chitin
- Viruses are non-living outside host
Quick Revision Notes
- 2 Kingdom → Linnaeus
- 5 Kingdom → Whittaker
- Monera = bacteria
- Protista = unicellular
- Fungi = decomposers
Frequently Asked Questions (FAQs)
Q1. Who proposed five kingdom classification?
R. H. Whittaker.
Q2. What is Monera?
Kingdom of prokaryotic organisms.
Q3. Are viruses living?
They are non-living outside host but active inside.
Q4. What is the cell wall of fungi made of?
Chitin.
Conclusion
Biological classification helps in understanding the diversity of life and evolutionary relationships among organisms. The five kingdom system provides a comprehensive framework and is essential for CBSE exams and NEET preparation.