The Living World - Notes (Class 11) | Part 2 - Diversity in the Living World

Diversity in the Living World

Taxonomy is the study of identification, classification & nomenclature of organisms.

Systematics (Latin ‘systema’ = systematic arrangement) deals with evolutionary relationships among organisms.

Characterization: Understanding of characters of organisms such as external & internal structure, cell structure, development process, ecological information, etc.
Identification: Correct description of the organism to enable naming.
Classification: Grouping of organisms into convenient categories (taxa) based on characters.
Nomenclature (naming): Standardization of names so an organism is known by the same name worldwide.

The system of naming with two components is called Binomial nomenclature. It was proposed by Linnaeus.
Botanical names are based on the rules in International Code for Botanical Nomenclature (ICBN).
Zoological names are based on International Code for Zoological Nomenclature (ICZN).

Scientific names are in Latin or Latinised and written in italics. When handwritten, they are underlined separately.
The first word is the genus name (Generic name) and the second word is the species name (specific epithet).
- E.g., Homo sapiens - Homo represents the genus name, and sapiens represents the species name.
The Genus name starts with a capital letter, and the species name starts with a small letter.
The name of the author (in abbreviated form) appears at the end of the biological name.
- E.g., Mangifera indica Linn. indicates this species was first described by Linnaeus.

Taxonomic Categories

Classification involves a hierarchy of steps, where each step represents a taxonomic category (rank).
All categories together constitute a taxonomic hierarchy.
A group of organisms occupying a particular category is called a taxon (pl. taxa). E.g., Class Mammalia.
Each category or taxon represents a unit of classification.

Species: A group of closely related organisms capable of interbreeding to produce fertile offspring. It is the lowest category.

Genus: An aggregate of closely related species.
- Potato, nightshade, and brinjal are species of genus Solanum.
- Lion, leopard, and tiger are species of genus Panthera. It differs from genus Felis (genus of cats).
Family: A group of closely related genera.
- Genus Solanum, Petunia, and Datura belong to Family Solanaceae.
- Genus Panthera and Felis belong to Family Felidae.
Order: An assemblage of related families.
- Families Convolvulaceae and Solanaceae belong to Order Polymoniales.
- Families Felidae and Canidae belong to Order Carnivora.
Class: An assemblage of related orders.
- Orders Primata, Carnivora, etc., belong to class Mammalia.
Phylum (Division in case of plants): An assemblage of related classes.
- Classes Amphibia, Reptilia, Aves, Mammalia, etc., come under phylum Chordata.
Kingdom: The assemblage of related phyla. It is the highest category.
- E.g., Kingdom Plantae, Kingdom Animalia.

Common name	Biological name	Species	Genus	Family	Order	Class	Phylum/Division	Kingdom
Man	Homo sapiens	sapiens	Homo	Hominidae	Primata	Mammalia	Chordata	Animalia
Housefly	Musca domestica	domestica	Musca	Muscidae	Diptera	Insecta	Arthropoda	Animalia
Mango	Mangifera indica	indica	Mangifera	Anacardiaceae	Sapindales	Dicotyledonae	Angiospermae	Plantae
Wheat	Triticum aestivum	aestivum	Triticum	Poaceae	Poales	Monocotyledonae	Angiospermae	Plantae

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