Bihar Board - Class 11 biology - Chapter 2: Biological Classification Handwritten Notes

Biological classification is the scientific method of organizing and categorizing living organisms into hierarchical groups based on their similarities, differences, and evolutionary relationships. It helps in understanding the vast diversity of life and the relationships between different species. This chapter introduces the history, principles, and systems of classification, including the modern taxonomic hierarchy.

Key Points

1. Need for Classification

   • Simplifies the study of millions of organisms by organizing them into groups.
   • Reveals evolutionary relationships and helps in understanding biodiversity.
   • Provides a universal naming system to avoid confusion caused by local names.

2. History of Classification

   • Aristotle: The first to classify organisms based on habitat (land, water, air).
   • Carolus Linnaeus: Introduced the binomial nomenclature and the hierarchical system of classification.

3. Modern Taxonomic Hierarchy

   • Organisms are classified into a series of ranks:
     • Kingdom → Phylum → Class → Order → Family → Genus → Species.
   • Species: The basic unit of classification; organisms within a species can interbreed.

4. Five Kingdom Classification
   Proposed by R.H. Whittaker in 1969, it divides organisms into five kingdoms:

   • Monera: Prokaryotic, unicellular organisms like bacteria and cyanobacteria.
   • Protista: Eukaryotic, unicellular organisms like algae, protozoa, and slime molds.
   • Fungi: Eukaryotic organisms with cell walls, such as mushrooms, molds, and yeast.
   • Plantae: Multicellular, eukaryotic autotrophs (plants).
   • Animalia: Multicellular, eukaryotic heterotrophs (animals).

5. Three-Domain System

   • Introduced by Carl Woese, it divides life into three domains based on genetic differences:
     • Bacteria: True bacteria, with prokaryotic cells.
     • Archaea: Prokaryotes living in extreme environments with unique biochemical traits.
     • Eukarya: Includes all eukaryotic organisms (protists, fungi, plants, and animals).

6. Kingdom Characteristics

   • Monera: Prokaryotic, unicellular, reproduces through binary fission.
   • Protista: Eukaryotic, unicellular or multicellular, both autotrophic and heterotrophic.
   • Fungi: Saprophytic, cell walls made of chitin, decomposers in ecosystems.
   • Plantae: Photosynthetic, cell walls made of cellulose, non-motile.
   • Animalia: Heterotrophic, no cell walls, highly motile.

7. Importance of Classification

   • Facilitates the identification and study of organisms.
   • Highlights evolutionary connections.
   • Aids in discovering new species and understanding extinct organisms.

8. Nomenclature

   • Binomial Nomenclature: Standardized naming system giving every organism a two-part name (Genus + Species), e.g., Homo sapiens.
   • Governed by the International Code of Botanical Nomenclature (ICBN) and International Code of Zoological Nomenclature (ICZN).

9. Tools of Classification

   • Taxonomic Keys: Used to identify organisms based on their traits.
   • Herbaria and Museums: Store specimens for research and reference.
   • Botanical Gardens and Zoological Parks: Preserve living organisms for study and conservation.

Conclusion

Biological classification is a vital tool in the study of life sciences, enabling a systematic and logical understanding of the diversity and complexity of life. It not only organizes organisms into meaningful groups but also reveals evolutionary relationships, aiding in scientific discoveries and biodiversity conservation.

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