THE LIVING WORLD - DIVERSITY IN THE LIVING WORLD

The Living World - Diversity in the living world

● There are various types of organisms that are present around us. They include microscopic living forms to giant plants and animals
There are millions of species present on earth. Number of species described is around 1.7-1.8 million.
The number and types of organisms present on earth is referred to Biodiversity.

● Each of these organisms are known by their local names which vary from one place to another. This creates confusion, and hence
a standardised system of naming has to be followed which is common throughout the world. Each organism is known by a single,
common name all over the world. This process of naming an organism is called Nomenclature. Common scientific name is
assigned to each organism.
Scientific names ensures that:
1. each organism has only one name
2. description of an organism should enable people anywhere in the world to arrive at the same name.
3. the name assigned to the described organism is not used to any other known organism.

● Nomenclature or naming is possible only when the organism is described correctly and we know to what organism the name is
attached to. This process is called identification.

● Scientific names are based on rules / principles and criteria provided by

ICBN - International Code for Botanical Nomenclature for naming plant and
ICZN - International Code for Zoological Nomenclature for naming animal
Binomial nomenclature :
It is the system of naming an organism with two components. According to this system, each scientific name has two
components - the first component is the Generic name and the second component is the specific epithet.
It is the universally accepted principle to provide scientific name to an organism.
This system was proposed by Carolus Linnaeus, father of modern taxonomy.

Universal rules of binomial nomenclature :

1. Biological names / scientific names are generally in latin.

2. Scientific name should have two words/components - First word represents genus while second word represents
species/specific epithet.

3. The generic name should begin with capital letter while specific epithet should begin with small letter.

4. If scientific name is handwritten, both generic name and specific epithet should be underlined separately. If typed/ printed, name
should be in italics.

5. The name of the author, who first described the species must be present after specific epithet in an abbreviated form.

Example: scientific name of mango - Mangifera indica Linn.

Here Mangifera represents a generic name while indica represents specific epithet. Linn indicates that this species was first
described by Linnaeus.
● Taxonomy : It is the branch of biology which deals with the classification of organisms into different taxa based on their
characteristics.

● Systematics : It is the branch of biology which deals with evolutionary relationship between organisms and their systematic
arrangement. It also include identification, nomenclature and classification.
It is derived from a latin word ‘Systema’, meaning systematic arrangement of organisms. Linnaeus used Systema Naturae as the
title of his publication.

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 we know to what organism the name is attached to.

• Classification: It is the grouping of organisms into convenient categories (taxa) based on some easily observable 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.
Categories : Categories are the groups of organisms with similar characters. Since the category is a part of overall taxonomic
arrangement, it is called the taxonomic category.
Each category is referred to as a unit of classification. It represents a rank and is commonly termed as taxon. Taxon is the basic
unit of classification.

Taxonomic hierarchy: Arrangement of taxonomic categories in an ascending order during classification is called Taxonomic
hierarchy. Each category in the taxonomic hierarchy is called taxon. In the taxonomic hierarchy, there are 7 categories arranged in an
ascending order.
Kingdom Taxonomic hierarchy in ascending order: E.g. Man
↑ Category Taxon
Phylum/division Kingdom Animalia
↑ ↑↑
Class Phylum/Division Chordata
↑ ↑↑
Order Class Mammalia
↑ ↑↑
Family Order Primata
↑ ↑↑
Genus Family Hominidae
↑ ↑↑
Species Genus Homo
↑↑
In ascending order - similarities decreases and differences increases. Species sapiens
In descending order - similarities increases and differences decreases.
Direction of the arrow changes
Species: It is a group of individual organisms with fundamental similarities. It is the lowest category / taxon.
E.g.
Generic name Specific epithet Common name
Mangifera indica Mango
Solanum tuberosum Potato
Solanum nigrum Black Nightshade
Solanum melongena Eggplant
Solanum lycopersicum Tomato
Panthera leo Lion
Panthera tigris Tiger
Panthera pardus leopard
Homo sapiens Modern man
Genus: It is the aggregate of closely related species.
Each genus may have more than one species representing different organisms but having morphological similarities. Even though
species are different, genus is the same as differences are more and similarities are less.
Ex:

Potato (Solanum tuberosum),Tomato (Solanum lycopersicum) Lion (Panthera leo), Leopard (Panthera. pardus)
Brinjal (Solanum melongena) - All are different species but Tiger (Panthera. tigris) - All are different species but belong to the
belong to the same genus Solanum. All are perennials. same genus Panthera. They all have spotted skin and similar in
cranial features.
Family: It is a group of closely related genera with less number of similarities as compared to genus and species.
Families are characterised on the basis of both vegetative and reproductive features of plant species.
Ex:
Animals - Genera Panthera ( lion, tiger, leopard) and Felis (cats)
Plants - Genera Solanum, Petunia and Datura are placed in
are placed in the same family Felidae.
the same family Solanaceae.
Similar in body shape, social living and hunting nature.
Similar in vegetative and reproductive features.
Order: It is the assemblage of families which exhibit a few similar characters.
Among plant, the families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral
characters.
Among animal, the families like Felidae (cats) and Canidae (dogs) are included in the order Carnivora. Mode of nutrition is
similar and they are domesticated. ( Felis catus , Canis lupus)

Class: It is the assemblage of closely related orders.

Ex: Order Primata and Order Carnivora are placed in class Mammalia. Mammary glands , directly give birth to young ones..
Order primata - monkey, gorilla and gibbon-apes , Order Carnivora - tiger, cat and dog.

Phylum / Division : It is the assemblage of related classes.

Classes Amphibia, Reptilia, aves, Mammalia are placed in the Phylum Chordata , based on the common features like presence
of notochord and dorsal hollow neural system.
In case of plants, closely related classes are grouped under Division - Angiospermae (closed seeded plants), Gymnospermae
(open seeded plants) .….

Kingdom: The assemblage of various phyla / division. It is the highest category.

Ex: All animals belonging to various phyla are assigned to the highest category called Kingdom Animalia. All plants from various
divisions are grouped under the Kingdom Plantae.