Diversity of Living World: Taxonomy, Classification, Kingdoms and Nomenclature
Domain 1: Diversity of Living World - what is tested
This domain checks whether you can place an organism correctly in the taxonomic hierarchy, apply binomial nomenclature, and distinguish the five-kingdom and three-domain systems. Tamil Nadu HSE questions often ask for defining features, examples, and the reason a group is classified as it is.
Core rules
- Taxonomy order: Domain, Kingdom, Phylum/Division, Class, Order, Family, Genus, Species. Species is the basic unit; genus is a group of related species.
- Binomial nomenclature: genus starts with a capital letter, species epithet is lower case; both are italicised in print or underlined separately in handwriting. The author abbreviation follows the species name in roman type.
- Whittaker's five kingdoms: Monera (prokaryotes), Protista (eukaryotic unicellular/colonial), Fungi (chitinous wall, absorptive heterotrophs), Plantae (cellulose wall, mostly autotrophs), Animalia (no wall, ingestive heterotrophs).
- Three-domain system separates Bacteria and Archaea from Eukarya; it does not replace the need to know kingdoms for this syllabus.
- Viruses are acellular obligate parasites; viroids are naked RNA; prions are infectious proteins. Lichens are symbiotic associations of algae/cyanobacteria and fungi.
Worked example
Place Mangifera indica L. in the hierarchy and explain the notation. Genus = Mangifera; species epithet = indica; L. = Linnaeus. It belongs to Kingdom Plantae, Division Angiospermae, Class Dicotyledonae, Order Sapindales, Family Anacardiaceae. The capital M and lower-case i are not optional: they show which word is the genus and which is the epithet.
Traps
Calling a species name the genus; writing Mangifera Indica; saying viruses are the smallest cells; confusing lichens with a single organism; listing kingdom before domain in the modern hierarchy; treating all Protista as autotrophic.