Chapter at a glance
- The living world shows vast biodiversity with 1.7–1.8 million known species; new organisms continue to be identified.
- Standardised naming (nomenclature) and identification are essential because local names vary; this is achieved through binomial nomenclature.
- Binomial nomenclature, given by Carolus Linnaeus, assigns each organism a scientific name with two components: generic name (genus) and specific epithet (species).
- Classification groups organisms into convenient categories (taxa) based on observable characters; the process is called taxonomy.
- Characterisation, identification, classification and nomenclature form the basic processes of taxonomy.
- Systematics is the branch that studies diversity, identification, nomenclature, classification and evolutionary relationships among organisms.
- All organisms are placed in a taxonomic hierarchy of categories (taxa) arranged in ascending order: species, genus, family, order, class, phylum/division, kingdom.
- Lower taxa share more common characters; higher taxa share fewer characters and relationships become more difficult to determine.
Definitions and laws
- Nomenclature: The process of standardising the naming of living organisms so that a particular organism is known by the same name all over the world.
- Identification: Correct description of an organism so that the name can be attached to it and people anywhere can arrive at the same name.
- Classification: The process by which anything is grouped into convenient categories based on some easily observable characters.
- Taxonomy: The branch dealing with characterisation, identification, classification and nomenclature of organisms; external and internal structure, cell structure, developmental process and ecological information form the basis of modern taxonomic studies.
- Systematics: The branch that takes into account evolutionary relationships between organisms in addition to identification, nomenclature and classification (derived from Latin “systema”).
- Taxonomic category / Taxon: Each rank or category in the overall taxonomic arrangement; all categories together constitute the taxonomic hierarchy.
- Species: A group of individual organisms with fundamental similarities; one species can be distinguished from another closely related species on the basis of distinct morphological differences.
- Genus: A group of related species that share more characters in common than species of other genera; genera are aggregates of closely related species.
- Family: A group of related genera with still fewer similarities than in a genus; characterised on the basis of both vegetative and reproductive features (plants) or other shared features (animals).
- Order: Assemblage of families that exhibit a few similar characters; similar characters are fewer than those shared by genera within a family.
- Class: Category that includes related orders.
- Phylum (animals) / Division (plants): Category comprising related classes.
- Kingdom: Highest category; all animals belonging to various phyla are placed in Kingdom Animalia; all plants from various divisions are placed in Kingdom Plantae.
Important diagrams and activities
- Figure 1.1 Taxonomic categories showing hierarchical arrangement in ascending order — demonstrates the sequence species → genus → family → order → class → phylum/division → kingdom with decreasing number of shared characters at higher levels.
- Table 1.1 Organisms with their Taxonomic Categories (examples: Man, Housefly, Mango, Wheat) — illustrates placement of common organisms into the complete hierarchy from species to kingdom.
Common misconceptions and exam pitfalls
- Writing the specific epithet with a capital letter (must start with small letter) or failing to underline/italicise both words of a binomial name.
- Reversing the hierarchy order (species is lowest, kingdom is highest).
- Confusing “genus” with “species” or stating that a genus has only one species (a genus may have one or more species).
- Using “phylum” for plants instead of “division”.
- Assuming all taxa at the same level share the same number of characters (higher taxa share fewer characters).
- Writing scientific names without the author’s abbreviated name when required (e.g., Mangifera indica Linn.).
Formula sheet
No mathematical formulas or equations appear in the chapter.