Science: Classification of Living Organisms: Biodiversity, Reproduction and Respiration (For CBSE, ICSE, IAS, NET, NRA 2022)

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What is Biodiversity

The enormous variety of organisms is termed biodiversity. There are organisms which are single celled and microscopic, as well as animals as large as the elephant, the rhinoceros, the hippopotamus and the whale. There is not only diversity in size among organisms but also in complexity. e. g. bacteria are simple single celled organisms and humans are made of a trillion cells and are highly complex.


Asexual, sexual, single parent, two parents


  • Oxygen from water, oxygen from atmosphere, Carbon dioxide into water, into atmosphere, gills, lungs, anaerobic, aerobic.
  • This part of the earth which supports life is the biosphere. Biosphere has diverse ecosystems such as the pond, river, oceans, and mountains, deserts etc. Various kinds of organisms or different species live in these ecosystems. They interact with each other and also interact with the physical components of the ecosystem such as light, temperature etc.

Levels of Biodiversity

All the varieties of living organisms on earth constitute biodiversity. Three levels of biodiversity have been recognized

Ecological/Ecosystem Diversity

Organisms evolved features which helped them adapt to their surroundings or the ecosystems in which they live. There are different ecosystems and even related organisms living in different ecosystems may differ vastly from each other. For Example, tortoises are terrestrial, and turtles are aquatic. Both are related but differ much especially in their feet.

Species Diversity

Variety of species living in a certain geographical area constitutes species diversity. Individual organisms belonging to a particular species are similar and are able to undergo reproduction to produce fertile offspring. They cannot interbreed with another species.

Genetic Diversity

Genetic Diversity

Organisms are made of cells and cells in their nuclei contain chromosomes which bear the genes. Genes control the features of a particular species. Genes of individuals belonging to the same species are similar.

Biodiversity Hotspots

Hotspots are regions of the world where many different kinds of organisms live.

India has two biodiversity ‘hotspots’ — the Western Ghats and North Eastern regions . Many of these organisms are not found elsewhere e. g. Many species of frogs live only in the Western Ghats of India.

Classification of Organism

  • Grouping of organism according to similarities and differences is termed classification.
  • When an organism is classified into various categories a hierarchy is maintained. Accordingly, an organism belongs to Kingdom, Phylum, Class, Order, Family, Genus and Species in hierarchical order.
  • These are groups to which an organism belongs, and which express its evolutionary relationship with other organisms.
  • Thus, classification shows evolutionary relationships between organisms and is also termed Systematics. The science of classification or systematics is termed Taxonomy.

The Three Domains of Classification

All organisms are now classified into three major domains:-

  • Archaebacteria: Archaebacteria are thermophilic or heat loving bacteria that live in high temperature vents.
  • Eubacteria: Eubacteria are single celled organisms without well-developed nucleus.
  • Eukarya: Eukaryaare all other organisms with a well-formed nucleus in their cell.
Three Domains of Classification

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