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

1. THE LIVING WORLD

DIVERSITY IN THE LIVING WORLD

·   The number and types of organisms present on earth refer to biodiversity.

·   Number of species described is 1.7-1.8 million.

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

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

·   Systema Naturae is the book written by Linnaeus.

Basic processes of taxonomy

·   Characterization: It is the understanding of characters of organisms such as external and internal structure, structure of cell, development process, ecological information etc.

·   Identification: It is the correct description of the organism so that the naming is possible.

·   Classification: It is the grouping of organisms into convenient categories (taxa) based on characters.

·   Nomenclature (naming): It is the standardization of names of the organisms such that an organism is known by the same name all over the world.

The system of naming with two components is called Binomial nomenclature. It is 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).

Universal rules of Binomial nomenclature

·   Scientific names are in Latin or Latinised and written in italics. When handwritten, they are underlined separately.

·   The first word is genus name (Generic name) and 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 capital letter and the species name starts with small letter.

·   Name of the author (in abbreviated form) appears at the end of the biological name.

E.g., Mangifera indica Linn. It indicates that this species was first described by Linnaeus.

TAXONOMIC CATEGORIES

-   Classification involves hierarchy of steps in which 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.

Taxonomic hierarchy in ascending order	Category	Taxon
	Kingdom	Animalia
	↑	↑
	Phylum/Division	Chordata
	↑	↑
	Class	Mammalia
	↑	↑
	Order	Primata
	↑	↑
	Family	Hominidae
	↑	↑
	Genus	Homo
	↑	↑
	Species	Sapiens

Species: It is a group of closely related organisms capable of interbreeding to produce fertile offspring.

It is the lowest category. E.g.

Common name	Generic name	Specific epithet
Mango	Mangifera	indica
Potato	Solanum	tuberosum
Nightshade	Solanum	nigrum
Tomato	Solanum	lycopersicum
Brinjal	Solanum	melongena
Lion	Panthera	leo
Tiger	Panthera	tigris
Leopard	Panthera	pardus
Modern man	Homo	sapiens

Genus: It is the aggregates of closely related species.

E.g. Potato, tomato & brinjal are species of genus Solanum. Lion, leopard & tiger are species of genus Panthera. This genus differs from genus Felis (genus of cats).

Family: It is a group of closely related genera. E.g.

Family Solanaceae includes Genus Solanum, Genus Petunia and Genus Datura.

Family Felidae includes Genus Panthera and Genus Felis.

Order: It is the assemblage of related families. E.g.

Order Polymoniales includes Family Convolvulaceae and Family Solanaceae.

Order Carnivora includes Family Felidae & Family Canidae. 

Class: It is the assemblage of related orders. E.g.

Order Primata, Carnivora etc. is placed in class Mammalia.

Phylum (Division in case of plants): It is the assemblage of related classes.

E.g. 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 etc.

Organisms with their taxonomic categories

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