DIVERSITY IN THE LIVING WORLD | Need of classification

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  • Biology (Bio- = life, -logy = study of) is the science of life forms and living processes.
  • Aristotle is a father of biology
  • Planet earth is made up of abiotic and biotic components.
  • The biotic components are the living beings present around us.
  • The abiotic components These includes the climate, temperature soil, water, organic compounds as proteins, carbohydrates, lipids etc. and inorganic substances like Calcium, Magnesium, phosphorus, Sulphur Nitrogen etc.
  • Life is a unique, complex organisation of ions and molecules which perform certain chemical reactions in order to being about life activities.
  • It includes growth, response, reproduction, cellular organisation, metabolism etc.


Basic principles of Life:

  • Metabolism:
  • Growth and development:
  • Ageing:
  • Reproduction:
  • Death:


  • Metabolism: – The sum total of all the reactions occurring in the body of an organism is called metabolism. Metabolism provides energy and many chemical molecules which is required for survival. Metabolism consist of two processes.
    1. Anabolism:
    2. Catabolism
  • Growth and development – All living organisms grow. Increase in mass and increase in number of individuals are twin characteristics of growth. A multicellular organism. grows by cell division. In plants, this growth by cell division occurs continuously throughout their life span. In animals, this growth is seen only up to a certain age. However, cell division occurs in certain tissues to replace lost cells. Unicellular organisms grow by cell division.
  • Ageing – Growth and development are not the processes which have unlimited time span. At certain point of time, the molecules, organs, systems begins to lose their effective working and become old. This is ageing process of the body.
  • Reproduction It is ability of organisms to produce new organism like itself. In unicellular organisms growth & reproduction are synonymous. Reproduction is of sexual & asexual type.
  • Death: When the capacity to perform metabolic reactions is lost. it results into death.



  • Enormous variety of living organisms exists on the earth. It is not possible for human beings to remember the characteristics of all these organisms without their systematic arrangement.
  • Described number of species range in 1.7- 1.8 million.
  • Local names of organisms may not be applied at global level.
  • Among the living organisms there is great diversity for their proper study and for understanding interrelationship, systematic and taxonomy is used
  • Systematics: Systematics is the scientific study of similarities and differences among different kinds of organisms and also it includes their identification, nomenclature and classification.
  • Taxonomy: It is the branch of biology which deals with the collection, identification, nomenclature, description and classification of plants and animals
  • Classification: It is the arrangement of organisms or groups of organisms in distinct categories in accordance with a particular and well-established plan.


Need of classification


  • There are a large number of living organisms found on earth. All these organisms show variations in their shape, size, structure, habit, habitat, nutrition etc. It gives universal, specific and scientific names to the organisms.
  • Scientific names are given to organisms after identification, acceptable at global level.
  • Nomenclature is done as per criteria given in:
    • ICBN = International code for botanical nomenclature
    • ICZN = International code for zoological nomenclature.
  • Binomial nomenclature was given by Carolus Linnaeus (Father of taxonomy)
    • Biological names are generally in Latin and written in italics. They are Latinised 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.


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