Kingdom Classification

A. What is Taxonomy?

Taxonomy is the branch of biology concerned with the systematic identification, nomenclature (naming), and classification of living organisms into groups based on structural and evolutionary similarities.

B. Binomial Nomenclature (Carolus Linnaeus, 1753):

A universal scientific system where every organism is assigned a unique two-part Latinized scientific name:

1. The first word is the Genus (Generic name); its first letter is ALWAYS CAPITALIZED (e.g., *Homo*).
2. The second word is the Species (Specific epithet); written in completely lowercase (e.g., *sapiens*).
3. In print, the scientific name is italicized (*Homo sapiens*); when handwritten, the Genus and species must be separately underlined (Homo sapiens).
4. Examples: Human (*Homo sapiens*), Tiger (*Panthera tigris*), Mango (*Mangifera indica*), Frog (*Rana tigrina*).

C. The 7 Taxonomic Hierarchy Levels:

Species: The fundamental, lowest unit of classification; a group of closely related organisms capable of freely interbreeding in nature to produce fertile offspring.

In 1969, Robert H. Whittaker classified all living organisms into Five Kingdoms based on cell complexity, body structure, and nutrition:

1. 1. Kingdom Monera (Prokaryotes):
   • Unicellular microscopic organisms lacking a defined nucleus and membrane-bound organelles (naked circular DNA in a nucleoid).
   • Cell wall present, made of peptidoglycan (not cellulose).
   • Autotrophic or heterotrophic. *Examples:* Bacteria, Cyanobacteria (Blue-green algae), Nostoc.
2. 2. Kingdom Protista (Unicellular Eukaryotes):
   • Unicellular organisms with a true membrane-bound nucleus and specialized organelles (mitochondria, ER).
   • Locomotion via pseudopodia (Amoeba), cilia (Paramecium), or flagella (Euglena).
   • *Examples:* *Amoeba* (holozoic), *Paramecium* (slipper animalcule), *Euglena* (mixotroph: photosynthesizes in light, hunts in dark!).
3. 3. Kingdom Fungi (Multicellular Decomposers):
   • Eukaryotic, mostly multicellular (except unicellular Yeast), non-green heterotrophs.
   • Plant body consists of filamentous thread-like hyphae forming a network called mycelium.
   • Cell wall made of tough Chitin (fungal cellulose).
   • Heterotrophic Nutrition: Saprophytic (absorb nutrients from dead decaying organic matter) or parasitic. No chlorophyll; cannot photosynthesize!
   • *Examples:* *Rhizopus* (bread mold), *Mucor*, *Agaricus* (mushroom), *Penicillium* (source of penicillin antibiotic), Yeast.
4. 4. Kingdom Plantae: Multicellular eukaryotic autotrophs with cellulose cell walls containing chlorophyll for photosynthesis (Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, Angiosperms).
5. 5. Kingdom Animalia: Multicellular eukaryotic heterotrophs with no cell walls, showing active locomotion and sensory nervous response.

Invertebrates are animals that lack a vertebral column (backbone), accounting for $95\%$ of all animal species:

• 1. Porifera (Pore-bearers): Sponges; sedentary aquatic animals with porous bodies (ostia) and a central osculum; cellular level of organization (e.g., *Sycon, Spongilla*).
• 2. Cnidaria / Coelenterata: Radially symmetrical aquatic animals with a central gastrovascular cavity and stinging cells (cnidoblasts/nematocysts) on tentacles (e.g., *Hydra, Jellyfish, Sea Anemone*).
• 3. Platyhelminthes (Flatworms): Dorsoventrally flattened, bilaterally symmetrical unsegmented worms; mostly parasitic (e.g., *Taenia* [Tapeworm], *Fasciola* [Liver fluke]).
• 4. Nematoda (Roundworms): Unsegmented, cylindrical worms with tapered ends; complete gut (e.g., *Ascaris* [human roundworm]).
• 5. Annelida (Segmented Worms): True metamerically segmented cylindrical bodies; possess a true coelom; locomotion via bristles (setae) (e.g., Earthworm [*Pheretima*], Leech [*Hirudinaria*]).
• 6. Arthropoda (Jointed-legged Animals): The LARGEST phylum in the entire animal kingdom ($>80\%$ of all species)! Body divided into head, thorax, and abdomen; jointed appendages; hard protective chitinous exoskeleton shed by moulting (e.g., Butterfly, Mosquito, Cockroach, Spider, Crab, Centipede).
• 7. Mollusca (Soft-bodied Animals): Soft, unsegmented bodies enclosed in a fleshy mantle that secretes a calcareous shell; muscular foot (e.g., Snail, Pila, Octopus, Pearl Oyster).
• 8. Echinodermata (Spiny-skinned Animals): Exclusively marine; spiny calcareous skin; radial symmetry in adults; unique water vascular system with tube feet (e.g., Starfish, Sea Urchin).

Vertebrates possess an internal skeletal backbone (vertebral column):

1. Class Pisces (Fishes): Aquatic, streamlined body, breathe via gills, fins for locomotion, cold-blooded (poikilothermic), 2-chambered heart (e.g., Rohu, Shark).
2. Class Amphibia (Amphibians): Dual life (water and land); moist slimy skin without scales; 3-chambered heart; undergo metamorphosis with aquatic tadpole stage (e.g., Frog, Toad, Salamander).
3. Class Reptilia (Reptiles): Creeping terrestrial vertebrates; dry scaly skin with epidermal scales; cold-blooded; 3-chambered heart (4-chambered in crocodiles); lay cleidoic shelled eggs (e.g., Lizard, Snake, Crocodile, Tortoise).
4. Class Aves (Birds): Forelimbs modified into wings for flight; body covered with insulating feathers; hollow pneumatic bones; warm-blooded (homeothermic); 4-chambered heart (e.g., Pigeon, Sparrow, Ostrich).
5. Class Mammalia (Mammals): Highest vertebrates; possess mammary glands to nourish young with milk; skin covered with hair/fur; external ear pinnae; warm-blooded; 4-chambered heart; viviparous giving birth to live young (e.g., Human, Whale, Bat, Kangaroo, Tiger).