Living organism is formed of many types of inorganic as well as organic biomolecules. Inorganic compounds include water, minerals etc. and are always micro-biomolecules (small sized, low molecular weight, readily soluble in water and diffusible) while organic molecules may be micro (e.g. monosugars, amino acids etc.) or macro­biomolecules (large sized, high molecular weight, insoluble or slightly soluble and non-diffusible e.g., proteins, fats, nucleic acids, etc.). These both types of biomolecules play important roles in metabolism.

  • 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 lifespan. 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.

  • The number of species that are known and described range between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth, hence there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.

  • Biologists follow universally accepted principles to provide scientific names to known organisms. Each name has two components – the Generic name and the specific epithet. This system of providing a name with two components is called Binomial nomenclature. This naming system was given by Carolus Linnaeus. The scientific name of mango is written as Mangifera indica.

  • Classification is the process by which anything is grouped into convenient categories based on some easily observable characters. For example, we easily recognise groups such as plants or animals or dogs, cats or insects.


  • Taxonomic categories

All living organisms can be classified into different taxa. This process of classification is taxonomy. The scientific term for these categories is taxa.

  1. The term taxonomy was coined by - A.P. Candolle

  2. Father of taxonomy - Carolus Linnaeus

  3. Father of Indian taxonomy - H. Santapau

  4. They are also known as Linnaean hierarchy.

  5. There are 7 main taxonomic categories. It is defined as the sequence of categories in a decreasing or increasing which is from the highest kingdom to the lowest species. The hierarchy has two categories i.e., obligate and intermediate. Obligate is the one which is followed strictly and range from kingdom to species. Intermediate is not followed strictly and they. Also they are added in obligate list like subdivision, super family, super class, suborder, subspecies etc.

a.  Species: It is the smallest taxonomic category. It is the basic unit of classification. It is the group of population which is similar in shape, form and reproductive features. Due to the same reproductive features, fertile sibling can be produced.

b.  Genus: It is an assembly of group of similar species which involved from a common ancestor and have certain common characters called correlated characters. But it is not mandatory to have many species. Monotypic genera have only one species. Polytypic genera have more than one species. For example, cat and leopard are put in genus Panthera.

c.  Family: It is the collection of similar genera. Families are characterised on the basis of reproductive and vegetative features. For example, lion and tiger are included in the family felidae.

d.  Order: Being a higher category is the assembly of one or more than one similar families. Family Felidae are included in the order Carnivora.

e.  Class: A class is a subdivision within a phylum made of one or more than one order. Class Mammalia includes all mammals which are monkey, gorilla, gibbon and man.

f.  Phylum: It comprises of collection of similar classes. Phylum Chordata of animals has class Mammalia along with fishes, reptiles, birds, and amphibians.

g. Kingdom: All animals belonging to various phyla are assigned to the top most taxonomic category called kingdom. Example all animals are included in Kingdom Animalia. All plants are included in kingdom Plantae. The unit that denotes grouping of organism based on observable features is known as Taxon.

                                    Taxonomic Description of Man

  • Taxonomic Aids

  1. The different methods which are being used to identify and classify organisms are referred to as Taxonomic aids. Identification of organisms is a tedious process.

  2. Keys are used for identification and are based on the contrasting characters. These are referred as Taxonomic key.

  3. Biologists use herbarium, botanical garden, museums, zoological parks and keys in taxonomical studies.

  4. Herbarium is a collection of plant parts that usually have been dried, pressed and preserved on sheets.

  5. Museums have collection of preserved plants and animal specimens for the study and reference.

This is probably the first chapter of biology in your text book, evidently it is one of the most important chapters, so make sure you clear out these concepts once and for all!