Diversity in Living Organisms

Diversity in Living Organisms

  • There are around 1.7-1.8 million species of living things in our worldwide.
  • Scientists have classified all living things into a system based on their physical traits.
  • All living things are classified into five Kingdoms which are further classified into phylum then class, order, family, genus, and finally species.
  • Biology is the study of life on earth as well as the evolution of living organisms on the earth.
  •  To differing degrees, all living organisms - present, past, and future - are linked through the sharing of shared genetic material.
  • "Biodiversity is the number and variety of organisms found on Earth.”
  • When there is a great deal of variability, it is necessary to standardise the naming of living organisms so that a certain organism is recognised by the same name all over the world.This is known as nomenclature.
  •  The biosphere on Earth contains a diverse array of living organisms (life forms), and the properties shared by these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon- and water-based cellular form with complex organisation and heritable genetic information.
  • Living organisms undergo metabolism, maintain homeostasis, have the ability to grow, respond to stimuli, reproduce, and, through natural selection, adapt to their environment. More complicated living organisms can communicate in a variety of ways.
  • Life and its nature are viewed differently in philosophy and religion. Both provide interpretations of how life connects to existence and consciousness, and both address a variety of connected topics, such as life stance, purpose, belief in a god or gods, a soul, or an afterlife.


Classification is the process by which anything is grouped into convenient categories based on some easily observable characters. “

History of  Classification 

  • Plants and animals were present on this planet before the human race evolved.
  • They gave names to the plants and animals, noted their features and even classified them in their own language.
  • Greek scholars Hippocrates (460 to377BC),often referred to as ‘Father of Medicine’ and Aristotle (384 to 322BC), often referred to as ‘Father of Biology’,’Father of Zoology’,’Father of Philosophy’ divided animals into four major groups like  insects,birds,fishes and whales.
  • Aristotle’s and Plato’s pupil Theophrastus (370 to 285 BC),often referred to as ‘Father of Botany’ ,in his book Historia Plantarum,classified plants on the basis of their habit, form and texture into four categories- trees, shrubs, undershrubs and herbs.
  • He gave name and description of 480 plants in his book.
  • In the late 17th century, John Ray, an English naturalist coined the term species for a group of morphologically similar organisms and also tried to differentiate between genus and species.
  • The terms, ‘monocotyledons’ and ‘dicotyledons’ were also coined by him.
  • Another significant period for taxonomy was that of Linnaeus.
  • Carolus Linnaeus (1707 to 1778), a Swedish naturalist, often referred to as ‘Father of taxonomy’ published Systema Naturae (1758) and described 5900 species of plants and these were arranged according to his system of classification based on sexual character.
  • Linnaeus also introduced a system of nomenclature of plants and animals known as the ‘Binomial Nomenclature’.
  • This phase of taxonomy led to the development of artificial system of classification.
  • Later, the organisms were classified on the basis of natural affinities (i.e., the basic similarities in the morphology).This phase represented the classical taxonomy and produced natural system of classification.
  • At the other end of the taxonomic spectrum, other biologists assigned taxonomic affinity based on evolutionary as well as genetic relationships among organisms besides morphology.
  • They ignored the morphological similarities or differences.
  • This resulted in development of “Phylogenetic Classification” or cladistics (Gk. Klados- branch, L.clados-branch).
  • Cladistics classifies organisms according to the historical order in which the evolutionary branches arose.
  • This led to the emergence of new systematics or Biosystematics.



  • Classification is the process by which anything is grouped into convenient categories based on some easily observable characters. “
  • The scientific term for these categories is taxa. Here you must recognize that taxa can indicate categories at very different levels. ‘Plants’ – also form taxa. ‘Wheat’ is also taxa.
  • All living organisms can be classified into different taxa on the basis of the characteristics. This process of classification is taxonomy.
  •  Hence, characterisation, identification, classification and nomenclature are the processes that are basic to taxonomy.
  • In early days, human beings needed to find sources for their basic needs of food, clothing and shelter. Hence, the earliest classifications were based on the ‘usesof various organisms.
  • The branch of science that deals with the study of principles and procedures of biological classification is called Taxonomy (A.P.de Candolle, 1813).


Importance of Classification

  • Classification makes the study of a wide variety of organisms easy. Classification is the tool by which one can deal with great diversity of living forms.
  • Classification projects before us a picture of all life forms at a glance.
  • Classification is essential to understand the interrelationships among different groups of organisms.
  • Classification forms a base for the development of other biological sciences.
  • Biogeography is totally dependent on the information supplied by classification. Likewise, the progress in the ecological and behavioral sciences (i.e., Ecology and Ethology) is not possible without accurate identification and Classification of an agricultural pest, a disease vector, a pathogen and a component of an ecosystem.



  • The science of giving names to living beings is called Nomenclature.
  • Two types of names are given to the organisms, common and scientific.
  • Common or Vernacular Names- These are the local names, which are given to the animals and plants in a particular language and region of the world by local persons. They are brief and easier to pronounce and remember by the residents of an area. They can’ not be used by biologists due to the following reasons-
  • Common names differ from region to region and language to language. An organism may have several names in a given language.
  • A common name may have different meanings in different areas.
  • Scientific or Technical names – Organisms must have a scientific name, which is acceptable all over the world. Such naming must be based on agreed principles and criteria.
  • The scientific names ensure that only one name is given to an organism and description of the organism, representing a species, is given a different name to distinguish it from the other.
  • One has to ensure that such a name has not been used earlier for any other organism.
  • The following have been the practices of providing scientific names to the organisms-
  • Polynomial - When a organism have more than one word name. E.g.-Caryophyllum saxatilis folis gramineus corymbis.
  • Binomial - When a organism have two word name. e.g. –Mangifera indica (mango), Apis mellifera (honey bee).
  • Trinomial- Occasionally three words are used for naming an organism e.g., Homo sapiens sapiens.
  • For plants, scientific names are based on agreed principles and criteria, which are provided in International Code for Botanical Nomenclature (ICBN).
  • Similarly animal taxonomists have evolved International Code of Zoological Nomenclature (ICZN).


Rules of Binomial Nomenclature

  • Universal rules of nomenclature are as follows-
  • Biological names are generally in Latin and written in italics.
  • They are Latinized or derived from Latin irrespective of their origin.
  • The first word in a biological name represents the genus while the second component denotes the specific epithet.
  • Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
  • The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter. It can be illustrated with the example of Mangifera indica.
  • Name of the author appears after the specific epithet, i.e., at the end of the biological name and is written in an abbreviated form, examples- Mangifera indica Linn. It indicates that this species was first described by Linnaeus.


New Systematics (Neosystematics or Biosystematics)

  • “The branch of study in which arrangement of organisms was done in systematic order is known as systematics.”
  • The word systematics is derived from the Latin word ‘systemawhich means systematic arrangement of organisms.
  • Linnaeus used Systema Naturae as the title of his publication.
  • New Systematics is a concept of systematics that considers a species to be the product of evolution.
  • It takes into consideration all the known characteristics of organisms and all the known evidences from different fields of biology.
  • The concept of new systematics was developed by Sir Julian Huxley in 1940.
  • The basic unit in new systematics is population.
  • Numerical taxonomy is also called phonetic or Adansonian Taxonomy(Adanson,1763).Turril (1938) used the term Omega (ω) Taxonomy for biosystematics or neosystematics.His Alpha (a) Taxonomy ( Turril, 1938) deals with collection and identification of organisms on the basis of gross morphology, compilation of flora and monographs.
  • Phylogeny and inter-relationship found between taxa on the basis of number, type and arrangement of chromosomes is karyotaxonomy.
  •  Cytotaxonomy is connected with cell organelles.
  •  Karyotaxonomy is based on organic evolution.
  •  Huxley is father of Neotaxonomy.