Biological Classification – Class 11 Biology Notes
Introduction
Biological classification is the scientific process of arranging organisms into groups based on similarities and differences. Earlier systems classified organisms only as plants or animals. However, as knowledge expanded, more detailed systems were developed.
One of the most widely accepted systems was proposed by R.H. Whittaker in 1969 — the Five Kingdom Classification.
Basis of Classification
The five-kingdom classification is based on:
- Cell structure (Prokaryotic or Eukaryotic)
- Body organization (Unicellular or Multicellular)
- Mode of nutrition (Autotrophic or Heterotrophic)
- Reproduction
- Phylogenetic relationships
Five Kingdom Classification
1. Kingdom Monera
- Key Characteristics:
- Prokaryotic organisms (no true nucleus)
- Unicellular
- Reproduce by binary fission
- Some have a cell wall (e.g., in bacteria), while others, like Mycoplasma, lack a cell wall.
- Examples:
- Bacteria
- Cyanobacteria (Blue-green algae)
- Mycoplasma
- Archaebacteria
- Special Types of Archaebacteria:
- Methanogens (produce methane)
- Halophiles (live in salty environments)
- Thermoacidophiles (live in hot, acidic environments)
2. Kingdom Protista
- Key Characteristics:
- Eukaryotic organisms (possess a true nucleus)
- Mostly unicellular
- Can be autotrophic (photosynthetic) or heterotrophic (consume other organisms)
- Found mostly in aquatic environments
- Groups of Protists:
- Chrysophytes (e.g., Diatoms)
- Dinoflagellates
- Euglenoids
- Slime molds
- Protozoans
- Examples:
- Amoeba (Protozoan)
- Paramecium (Protozoan)
- Euglena (Euglenoid)
3. Kingdom Fungi
- Key Characteristics:
- Eukaryotic
- Multicellular (except yeast, which is unicellular)
- Heterotrophic (saprophytic or parasitic)
- Cell wall made of chitin
- Reproduce by spores
- Common Groups of Fungi:
- Phycomycetes
- Ascomycetes
- Basidiomycetes
- Deuteromycetes
- Examples:
- Mushrooms
- Rhizopus (bread mold)
- Yeast
- Penicillium
4. Kingdom Plantae
- Key Characteristics:
- Multicellular
- Eukaryotic
- Autotrophic (photosynthesis)
- Cell wall made of cellulose
- Contain chloroplasts for photosynthesis
- Major Groups of Plantae:
- Algae
- Bryophytes (non-vascular plants like mosses)
- Pteridophytes (vascular plants like ferns)
- Gymnosperms (cone-bearing plants)
- Angiosperms (flowering plants)
5. Kingdom Animalia
- Key Characteristics:
- Multicellular
- Eukaryotic
- Heterotrophic (consume food)
- No cell wall
- Generally exhibit movement at some stage in life
- Examples:
- Invertebrates (e.g., Earthworm, Starfish)
- Vertebrates (e.g., Fish, Frog, Human)
Viruses, Viroids, and Lichens
Viruses
- Characteristics:
- Acellular (not made of cells)
- Can only reproduce inside a host cell
- Made of a protein coat and genetic material (either DNA or RNA)
- Example: Tobacco Mosaic Virus (TMV)
Viroids
- Characteristics:
- Smaller than viruses
- Consist only of RNA (no protein coat)
- Cause plant diseases
Lichens
- Characteristics:
- Symbiotic relationship between algae and fungi
- Algae (or cyanobacteria) photosynthesize and provide food
- Fungi provide shelter and moisture
- Important as bioindicators of air quality
Important Differences
Prokaryotic vs Eukaryotic
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Absent | Present |
| Size | Smaller | Larger |
| Organelles | Absent | Present |
| Examples | Bacteria | Plants, Animals |
Important MCQs – Biological Classification
1. Who proposed the five-kingdom classification?
a) Linnaeus
b) R.H. Whittaker
c) Darwin
d) Aristotle
Answer: b) R.H. Whittaker
2. Which kingdom includes prokaryotic organisms?
a) Protista
b) Fungi
c) Monera
d) Plantae
Answer: c) Monera
3. The cell wall of fungi is made up of:
a) Cellulose
b) Chitin
c) Peptidoglycan
d) Lipid
Answer: b) Chitin
4. Diatoms belong to:
a) Fungi
b) Protista
c) Plantae
d) Monera
Answer: b) Protista
5. Lichens represent:
a) Parasitism
b) Symbiosis
c) Saprophytism
d) Commensalism
Answer: b) Symbiosis
6. Mycoplasma lacks:
a) Cell membrane
b) Ribosomes
c) Cell wall
d) DNA
Answer: c) Cell wall
7. Viruses are:
a) Prokaryotic
b) Eukaryotic
c) Cellular
d) Acellular
Answer: d) Acellular
8. Which kingdom includes unicellular eukaryotes?
a) Protista
b) Monera
c) Animalia
d) Plantae
Answer: a) Protista
9. Methanogens belong to:
a) Fungi
b) Protista
c) Archaebacteria
d) Algae
Answer: c) Archaebacteria
10. Yeast is:
a) Bacteria
b) Protist
c) Fungi
d) Plant
Answer: c) Fungi