Classification of Living Organisms Tnpsc

Three domains of classification

All the organisms are classified into 3 major domains.


They are thermophilic or heat-loving bacteria. These bacteria live in high-temperature vents.


Eubacteria is a single-celled organism that is without a well-developed nucleus.


Eukarya means ‘True Nucleus’. Eukarya are organisms that have a well-formed nucleus in their cell/cells.

Five Kingdoms of Life

In the beginning, living beings have been classified only into two categories, that is plants and animals. But in 1969 Whittaker suggested that the bacteria should not be in the plant kingdom and protozoa should be in the Animal kingdom.

Thereby Whittaker suggested five-kingdom classifications. The Five kingdoms of living beings are:

  1. Monera
  2. Protista
  3. Fungi
  4. Plantae
  5. Animalia


It is single-celled. It does not have a well-formed nucleus (Prokaryotes).


It is single-celled with a well-formed nucleus (Eukaryotes).


It is Eukaryotes and it is multicellular called Saprotrophs.


It is eukaryotes, multicelled, and is heterotrophs.

These five-kingdom are further divided into several divisions i.e As bacteria, fungi, and Plantae or Phyla (Protoctista and Animalia). A family is made of several genera (Genus). Each genus has many species.

Every species are separated from their related species under the same genus by reproductive barriers. That is a member of one species cannot interbreed with another species to produce fertile offspring.

Example: Lion and Tiger cannot interbreed, Donkey and Zebra cannot interbreed, Humans and Chimpanzee cannot interbreed, etc.

Classification of Animals

  • Non-Chordata
    • Phylum Porifera
    • Phylum Cnidaria
      • Phylum Aschelminthes
      • Annelida
      • Phylum Arthropoda
      • Echinodermata
      • Phylum Mollusca
    • Phylum Platyhelminthes
  • Chordata
    • Phylum Chordata
      • Sub-Phylum Vertebrata
        • Class Chondrichthyes
        • Class Osteichthyes
        • Class Amphibia
        • Class Reptilia
        • Class Aves
        • Class Mammalia


Phylum Porifera

  • Irregular Body, with Pores or Ostia for water entry with oxygen and food.
  • It has tiny pieces of sponge that can regenerate into complete individual.
  • Example: Sycon, Sponge

Phylum Cnidaria

  • Cnidaria has tentacles surrounded mouth.
  • It has presence of stinging cells.
  • It does reproduction by budding or sexual.
  • Example: Hydra, Jellyfish, Corals, Anemones.

Phylum Aschelminthes

  • Their body is round.
  • They are parasitic or free living
  • Example: Ascaris(Round), Pin worms


  • Their body is segmented
  • They excrete by nephridia.
  • They are hermaphrodite. That is both male and female organs in the same individual.
  • Example: Earthworm, leech, Nereis

Phylum Arthropoda

  • They have jointed legs
  • Their body are divided into head, thorax, abdomen
  • Their body covered with cuticle (layer above skin) made of hard substance called Chitin.
  • Example: Insects, Spider, Scorpions, Prawns, crabs.


  • They are flat or globular, and are deep sea animals.
  • They have 5 arms or division of body. They have spiny Skin.
  • Example: Star Fish

Phylum Mollusca

  • They are soft, unsegmented body which is enclosed in the hard shell made of calcium carbonate.
  • They has muscular foot
  • Example: Oysters, Snails, Octopus etc.

Phylum Platyhelminthes

  • It has flat body. They are mostly parasitic worms and some free livings.
  • Example: Tape Worm, Liver Fluke, Planaria

Phylum Chordata

Class Chondrichthyes

  • They have skeleton made of cartilage.
  • They have seven pais of gill slits such as marine fish
  • Example: Sharks, Rays

Class Osteichthyes

  • They have bony skeleton.
  • They are found in both sea and fresh water.
  • The gills are used breathing that are covered by operculum.
  • Example: Rohu, Catla.

Class Amphibia

  • They live on the land but they lay egg in the water.
  • They are adapted to live in both water and land.
  • They breath with their lungs.
  • Example: Salamanders, Frog.

Class Reptilia

  • These are land animals mostly and lay their eggs on the land.
  • Their body is covered with scales.
  • Example: Lizard, Snake, Crocodile, turtle

Class Aves

  • These are aerial mode of lives. They have light bones.
  • They have beak for feeding. They have wings for flying.
  • Ex: Eagle, Crow

Class Mammalia

  • They have mammary gland for producing milf for their younger ones.
  • Their body is covered with hair.
  • Example: Man, Dog, Cow etc.

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* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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