SYSTEMATICS OF LIVING - Class 11 Maharashtra Board History

Systematics of Living Organisms

Meaning and Scope of Systematics

Systematics is the scientific study of the diversity of living organisms and their evolutionary relationships. It involves the identification, classification, and nomenclature of organisms based on comparative and evolutionary criteria. The aim is to categorize organisms into groups that reflect their natural relationships and evolutionary history.

• Systematics includes taxonomy (classification based on rules) and phylogeny (evolutionary relationships).
• Taxon: Any group or rank in a classification system (e.g., species, genus, family).
• The term "taxon" was introduced by A.P. de Candolle.

Historical Systems of Classification

Classification systems…

Systematics of Living Organisms

Meaning and Scope of Systematics

Systematics is the scientific study of the diversity of living organisms and their evolutionary relationships. It involves the identification, classification, and nomenclature of organisms based on comparative and evolutionary criteria. The aim is to categorize organisms into groups that reflect their natural relationships and evolutionary history.

• Systematics includes taxonomy (classification based on rules) and phylogeny (evolutionary relationships).
• Taxon: Any group or rank in a classification system (e.g., species, genus, family).
• The term "taxon" was introduced by A.P. de Candolle.

Historical Systems of Classification

Classification systems have evolved from simple artificial groupings to complex phylogenetic frameworks. Early systems relied on observable features, while later systems incorporated anatomical, chemical, and evolutionary data.

• Artificial System: Based on a few easily observable features (e.g., habit, color). Given by Linnaeus.
• Natural System: Considers morphological, anatomical, and chemical characters. Developed by Bentham and Hooker.
• Phylogenetic System: Based on evolutionary relationships and common ancestry. Proposed by Engler and Prantl.
• Cladogram: A branching diagram showing hypothetical evolutionary relationships.

Three Domains of Life

Life forms are classified into three major domains based on cell structure and molecular analysis. This system was proposed by Carl Woese in 1990.

• Domains:
  • Bacteria: Prokaryotic, cell wall with peptidoglycan.
  • Archaea: Prokaryotic, cell wall without peptidoglycan (pseudopeptidoglycan), survive in extreme conditions.
  • Eukarya: Eukaryotic, includes kingdoms Plantae, Animalia, Fungi, and Protista.
• Domains are higher than kingdoms in the taxonomic hierarchy.

Methods and Tools in Modern Taxonomy

Modern taxonomy uses various methods to classify organisms, including chemical, numerical, and molecular approaches.

• Chemotaxonomy: Classification based on chemical composition (e.g., cell wall components like chitin in fungi, cellulose in plants).
• Numerical Taxonomy: Uses quantification of characters and computer algorithms to group organisms based on similarity.
• DNA Barcoding: Identification of species using DNA sequence data from a small tissue sample. Involves:
  1. Collecting DNA barcode data from known species.
  2. Matching unknown samples against the barcode library.
• Cladogram: Visual representation of evolutionary relationships based on shared derived characters.

Taxonomic Hierarchy and Ranks

Taxonomic hierarchy is the arrangement of taxonomic categories in a series of ascending or descending order. Each rank is called a taxon.

• Hierarchy (from smallest to largest):
  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum/Division
  • Kingdom
  • Domain
• Each rank groups organisms with shared characteristics; for example, all species in a genus are closely related.

Binomial Nomenclature

Binomial nomenclature is the system of naming organisms with two Latinized words: the genus and the species. This system ensures universal identification.

• Rules:
  • The first word is the genus (capitalized), the second is the species (lowercase).
  • Both words are italicized or underlined.
  • The genus name can be abbreviated after first use.
  • The scientific name may be followed by the authority (e.g., Mangifera indica L., where "L." stands for Linnaeus).
  • The name should have at least 3 and not more than 13 letters.

Five Kingdom System of Classification

R.H. Whittaker proposed the Five Kingdom System, classifying all living organisms into five kingdoms based on cell structure, mode of nutrition, and reproduction.

• Kingdoms:
  • Monera: Prokaryotic, unicellular, cell wall with peptidoglycan, asexual reproduction (binary fission, budding, conjugation), includes bacteria and cyanobacteria.
    • Archaebacteria: Survive in extreme conditions (halophiles, thermophiles, methanogens).
    • Eubacteria: True bacteria, various nutritional modes (autotrophic, heterotrophic).
    • Mycoplasma: Bacteria without cell wall, smallest living cells, can survive without oxygen.
  • Protista: Unicellular eukaryotes, includes plant-like (algae), animal-like (protozoa), and fungus-like protists.
    • Plant-like: Chrysophytes (diatoms), dinoflagellates, euglenoids.
    • Animal-like: Protozoa (amoeboid, flagellated, ciliated, sporozoan).
    • Fungus-like: Slime molds (plasmodium stage).
  • Fungi: Eukaryotic, unicellular or multicellular, cell wall of chitin, heterotrophic (saprophytic, parasitic, predatory), reproduce sexually and asexually.
    • Groups: Phycomycetes (aseptate hyphae), Ascomycetes (sac fungi), Basidiomycetes (club fungi), Deuteromycetes (imperfect fungi).
    • Lichens: Symbiotic association of algae (phycobiont) and fungi (mycobiont), indicator of pollution.
  • Plantae: Multicellular, eukaryotic, autotrophic (chlorophyll), cell wall of cellulose, alternation of generations (gametophyte and sporophyte stages).
    • Groups: Thallophyta, Bryophyta, Pteridophyta (cryptogams: hidden reproductive organs), Gymnosperms, Angiosperms (phanerogams: exposed reproductive organs).
    • Special types: Insectivorous plants (Venus flytrap), parasitic plants (Cuscuta).
  • Animalia: Multicellular, eukaryotic, heterotrophic, no cell wall or chlorophyll, determinate growth, mostly capable of locomotion, sexual and asexual reproduction.

Viruses, Viroids, and Prions

Viruses are acellular infectious agents at the threshold of life, showing both living and non-living characteristics. They require a host cell for replication.

• Viruses:
  • Composed of a protein coat (capsid) and genetic material (DNA or RNA).
  • Can be crystallized outside host cells (Stanley).
  • Named by Pasteur; "virus" means venom or poison.
  • Types: DNA viruses, RNA viruses, bacteriophages (infect bacteria).
  • Cause diseases like leaf curling, mosaic formation in plants, foot and mouth disease in animals, and various human diseases (e.g., AIDS, smallpox, mumps, herpes, common cold).
• Viroids:
  • Discovered by T.O. Diener (1971).
  • Smaller than viruses, consist of free RNA without a protein coat.
  • Cause diseases like potato spindle tuber disease.
• Prions:
  • Infectious agents made of abnormally folded proteins.
  • Cause neurological diseases (e.g., mad cow disease in cattle, Creutzfeldt-Jakob disease in humans).

Key Features and Exam Points

Understanding the distinguishing features, classification criteria, and examples is crucial for exams. Focus on the following:

• Monera: Prokaryotic, cell wall composition, reproduction methods, shapes (coccus, bacillus, vibrio, spirillum), groups (archaea, eubacteria, mycoplasma).
• Protista: Eukaryotic, unicellular, plant-like (photosynthetic), animal-like (heterotrophic), fungus-like (saprophytic), examples (diatoms, dinoflagellates, euglenoids, amoeba, paramecium, plasmodium).
• Fungi: Eukaryotic, chitin cell wall, hyphae (septate/aseptate), reproduction (spores, fragmentation), groups and examples, lichens as pollution indicators.
• Plantae: Multicellular, autotrophic, cell wall of cellulose, alternation of generations, cryptogams vs. phanerogams, special adaptations (insectivorous, parasitic).
• Animalia: Multicellular, heterotrophic, no cell wall, determinate growth, locomotion, reproduction.
• Viruses/Viroids/Prions: Structure, replication, diseases caused, distinguishing features.

Table: Key Differences in Cell Wall Composition

• This table summarizes the main cell wall components as explicitly stated.

Nomenclature and Classification Rules

Correct application of nomenclature and classification rules is essential for scientific communication.

• Binomial nomenclature: Two-word Latin name (Genus species), genus capitalized, species lowercase, italicized/underlined.
• Taxonomic hierarchy: Each rank (species, genus, family, etc.) is a taxon.
• Classification criteria: Based on cell structure, nutrition, reproduction, evolutionary relationships, and chemical composition.
• MCQ focus: Cell wall composition, examples of each group, distinguishing features, and special adaptations are common exam questions.