Systematics and Taxonomy Overview

Systematics and Taxonomy

• Systematics is the study of organism diversity and their relationships.
• Taxonomy is the classification of organisms based on rules and principles.
• Classification involves grouping organisms based on a plan, with ranks forming a hierarchy.
• Chemotaxonomy uses chemical characteristics for classification, like cell wall composition.
• Numerical taxonomy compares organisms based on many characteristics from different fields of biology.
• Cladograms show hypothetical relationships between organisms and their ancestors.
• Phylogeny considers both morphology and evolutionary relationships between organisms.
• DNA barcoding identifies species using DNA sequences from tissue samples.

Binomial Nomenclature

• Carl Linnaeus proposed the Binomial Nomenclature system.
• Binomial Nomenclature comprises two words: Genus (first word, capitalized noun) and species (second word, lowercase adjective).
• Both names are written in italics or underlined if handwritten.
• The author who named the organism is also written in full or abbreviated form.
• The system avoids confusion caused by vernacular names, which vary by region.

Five Kingdom Classification

• The Five Kingdoms were proposed by R.H. Whittaker.
• Kingdom Monera:
  • Lacks membrane-bound organelles (chloroplasts, mitochondria, etc.).
  • 70S ribosomes.
  • Reproduction via asexual methods like binary fission, budding, or rarely, sexual (conjugation).
  • Bacteria shapes include: coccus (spherical), bacillus (rod-like), vibrio (comma-shaped), spirillum (spiral).
  • Two types of bacteria based on evolution:
    • Archebacteria: Extremophiles (halophiles, thermophiles) found in harsh environments.
    • Eubacteria: True bacteria with peptidoglycan cell walls, can be autotrophs or heterotrophs.
  • Useful bacteria: Lactobacilli (curdling milk), Azotobacter (nitrogen fixation), Streptomyces (antibiotic production).
  • Harmful bacteria: Cause diseases like typhoid, cholera, tuberculosis, and tetanus.
  • Mycoplasma: Smallest living organisms without cell walls, resistant to antibiotics, can be pathogenic.
• Kingdom Protista:
  • Connects unicellular Kingdom Monera to eukaryotic Kingdoms Plantae, Fungi, and Animalia.
  • Plant-like Protists (Chrysophytes / Phytoplanktons): Photosynthetic, major ocean producers.
    • Diatoms: Cell wall made of silica, two fitting covers.
    • Diatomaceous earth: Granular sediment from diatom shells, used in polishing and filtration.
  • Animal-like Protists (Protozoans): Lack cell walls.
    • Amoeboid Protozoans: Move with pseudopodia (e.g., Amoeba, Entamoeba).
    • Flagellated Protozoans: Move with flagella (e.g., Trypanosoma).
    • Ciliated Protozoans: Move with cilia (e.g., Paramoecium).
    • Sporozoan Protozoans: Parasitic, produce spores (e.g., Plasmodium).
  • Dinoflagellates: Mostly marine, photosynthetic, cellulose cell walls, Gonyaulax causes "Red Tides."
  • Fungi-like Protists: Saprophytic, form plasmodium, produce spores.
  • Euglenoids: Lack cell walls, have a pellicle (protein layer), autotrophic in light, heterotrophic in darkness.
• Kingdom Plantae:
  • Mostly autotrophs, some are semi-autotrophic (insectivorous) or heterotrophic (parasitic).
  • Divided into Cryptogams (non-flowering plants) and Phanerogams (flowering plants).
• Kingdom Fungi:
  • Fungal body called mycelium, made of hyphae.
  • Hyphae can be septate (divided) or aseptate (undivided).
  • Multinucleate coenocytic hyphae are common (undivided hyphae with many nuclei).
  • Cell wall made of chitin or fungal cellulose.
  • Reproduction can be sexual or asexual (fragmentation, fission, budding).
  • Heterotrophic with extracellular digestion, relying on dead organisms for food.
  • Some are parasitic, predatory, or symbiotic.
  • Useful Fungi: Food (mushroom, morels, truffles), baking/brewing (Saccharomyces), antibiotic production (Penicillium), research (Neurospora).
  • Harmful Fungi: Disease causing (Albugo, Puccinia, Ustilago).

Classification of Fungi

• Kingdom Fungi:
  • Deuteromycetes (Imperfect Fungi): Sexual reproduction not known, mycelium aseptate and coenocytic. Example: Alternaria.
  • Phycomycetes (Algal Fungi): Mycelium aseptate and coenocytic. Example: Rhizopus.
  • Ascomycetes (Sac Fungi): Mycelium septate. Examples: Penicillium, Neurospora.
  • Basidiomycetes (Club Fungi): Mycelium septate. Examples: Plant diseases like rusts, smuts.

Viruses and Viroids

• Viruses:
  • Genetic material (DNA or RNA) enclosed in a protein coat (capsid).
  • Cause diseases in plants and animals.
  • Plant diseases: Leaf curling, yellowing, mosaic formation.
  • Animal diseases: Foot and mouth disease, smallpox, mumps, herpes, common cold, AIDS, COVID.
• Viroids:
  • Low molecular weight RNA, lack protein coat, smaller than viruses.
  • Cause potato spindle tuber disease.
  • Differences between viruses and viroids:
    • Viruses have a capsid, viroids do not.
    • Viruses are larger than viroids.
    • Viruses can have DNA or RNA, viroids always have RNA.

Lichens

• Lichens: Symbiotic association between an algae (phycobiont) and a fungus (mycobiont).
• Algae provide food, fungus provides shelter, water, and minerals.
• Found in extreme environments, sensitive to pollution, considered pollution indicators.