Living organisms show a wide variety in size, lifespan, and other characteristics. To effectively study and understand such diversity, organisms must be classified into groups based on their similarities. The main characteristics used to classify organisms include their cellular structure, whether they are unicellular or multicellular, how they obtain nutrition, and the complexity of their body organization. This classification system arranges organisms in a hierarchy of nested groups from the broadest domain of life down to specific species. The five kingdom system proposed by Robert Whittaker in 1959 is still widely used, dividing organisms into Monera, Protista, Fungi, Plantae, and Animalia.

2. Need for classification of living organisms :-
Living organisms have evolved on the earth over millions of years.
There is a vast variety of living organisms. Living organisms show a
wide range of variations.
- Some microscopic bacteria are of a few micrometres in size and some
like whales and red wood trees are about 30 metres and 100 metres in
size.
- Some pine trees live for thousands of years while insects like
mosquitoes die within a few days.
- Some organisms are colourless and even transparent and some are
brightly coloured.
To understand and study all these organisms is impossible. If they are
arranged into different groups based on their similarities in
characteristics, then it is easier to study the different groups as a
whole.
Classification of living organisms :- The arranging of organisms
into different groups on the basis of the similarities in their
characteristics is called classification of living organisms.

3. Basis of classification of living organisms :-
The main characteristics which are considered for
classification of living organisms into different groups are :-
- Whether they are made of prokaryotic or eukaryotic cells.
- Whether the cells occur singly or they are grouped
together and live as an indivisible group.
- Whether they produce their own food by photosynthesis
or get their food from outside.
-Of the organisms which produce their own food (plants)
what is the level of organisation of their body ?
- Of the animals what is the level of organisation of their
body and what are their special organs and their
functions ?
The characteristics used for classification of plants will be
different from the characteristics used for classification of
animals because plants make their own food and animals
get their food from outside.

4. Classification and evolution :-
The present day complex living organisms have evolved
from the earlier simple forms due to the changes in their
body designs over millions of years.
The body designs of living organisms are gradually
changing due to the changes in environment and the need
to adapt themselves to the changes in the environment.
Some groups of organisms having ancient body designs
have not changed much during evolution and have simple
forms and structure. These organisms are called ‘primitive
or lower organisms’.
Some organisms have acquired their body designs
relatively recently and have complex forms and structure.
These organisms are called ‘advanced or higher
organisms’.

5. The hierarchy of classification – Groups
Living organisms have been broadly classified into five main
kingdoms. They are :-
i) Monera ii) Protista iii) Fungi iv) Plante v) Animalia
Each kingdom has been further classified into smaller
sub - groups at various levels as :-
Kingdom
Phylum (for plants) / Division (for animals)
Class
Order
Family
Genus
Species
By arranging organisms on the basis of hierarchy and characteristics
into smaller and smaller groups we arrive at the basic unit of
classification called species.
Species :- is group of organisms which are similar enough to breed
and perpetuate.

6. The basis for grouping
organisms into five kingdoms
• i) On the basis of the presence or absence of membrane-bound
organelles, all living organisms are divided into two broad
categories of eukaryotes and prokaryotes. This division lead to
the formation of kingdom Monera, which includes all
prokaryotes.
• (ii) Then, eukaryotes are divided as unicellular and
multicellular, on the basis of cellularity. Unicellular eukaryotes
form kingdom Protista, and multicellular eukaryotes form
kingdom Fungi, Plantae, and Animalia.
• (iii) Animals are then separated on the basis of the absence of
a cell wall.
• (iv) Since fungi and plants both contain a cell wall, they are
separated into different kingdoms on the basis of their modes
of nutrition. Fungi have saprophytic mode of nutrition, whereas
plants have autotrophic mode of nutrition. This results in the
formation of the five kingdoms
•

7. Five kingdom system of
classification
• Robert .H. Whittaker in 1959 proposed
a five kingdom classification of living
organisms on the basis of Linnaeus’
system of classification encorporating
cell structure, mode and source of
nutrition and body organisation as
main features. The five kingdoms
proposed by Whittaker are Monera,
Protista, Fungi, Plantae, and Animalia

8. The Five Kingdom classification of living organisms :-
Organisms
Prokaryotes Eukaryotes
Unicellular Multicellular
Protista
With cell wall Without cell wall
Animalia
Do not perform
photosynthesis
Able to perform
photosynthesis
Fungi Plantae
Monera

9. Monera :-
1. They are mostly prokaryotic,
2. unicellular
3. Do not have a definite nucleus
4. May or may not have cell wall
5. Mode of nutrition is autotrophic or heterotrophic.
Eg :- Bacteria, Blue-green algae, Cyanobacteria, Mycoplasma etc.
Bacteria
Blue-green algae
Cyanobacteria
Mycoplasma

10. Protista :-
 They are eukaryotic
 unicellular
 Mostly aquatic, some have cilia or flagella which help them in moving
 Mode of nutrition may be autotrophic or heterotrophic.
 Eg :- Algae, Diatoms, Protozoans etc.
Algae
Protozoan
Diatoms

11. Fungi :-
• They are eukaryotic, multicellular.
•They do not have chlorophyll and cannot prepare their own food and
are heterotrophs. They use decaying organic matter as food and so
are called saprophytes.
• Some of them live in association with algae. They are called lichens.
•Eg :- Yeast, Aspergillus, Penicillium, Agaricus, Lichens etc.
Yeast
Agaricus
Lichens

12. Plantae (Plants)
They are multicellular eukaryotes having cell walls.
They use chlorophyll for photosynthesis. All plants are
included in this group.
They are divided into five groups. They are :-
Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and
Angiosperms.
.

13. Animalia (Animals)
• They include all organisms which are multicellular,
eukaryotes,
• Without chlorophyll and cell walls.
• They are heterotrophs.
• They are divided into ten groups.
• They are :-
• Porifera, Coelenterata, Platyhelminthes, Nematoda,
• Annelida, Arthropoda, Mollusca, Echinodermata,
• Protochordata, and Vertebrata

14. Classification of plants
• (i) The first level of classification depends on whether a plant body is
well differentiated or not. A group of plants that do not have a well
differentiated plant body are known as Thallophyta.
• (ii) Plants that have well differentiated body parts are further divided
on the basis of the presence or absence of vascular tissues. Plants
without specialised vascular tissues are included in division
Bryophyta, whereas plants with vascular tissues are known as
Tracheophyta.
• (iii) Tracheophyta is again sub-divided into two divisions Pteridophyta
and Phanerogams on the basis of the absence/presence of seed
formation.
• (iv) Pteridophyta plants do not produce seeds
• (iv) Phanerogams plants have well developed reproductive organs that
finally produce seeds.
• (v) Phanerogams group is further sub- divided on the basis of whether
the seeds are naked or enclosed in fruits. This classifies them into
gymnosperms and angiosperms.
• Gymnosperms are seed bearing, non-flowering plants, whereas
angiosperms are flowering plants in which the seeds are enclosed
inside the fruit.
•

15. Classification of plants (Plantae) :-
Plants are divided into five groups. They are :-
i) Thallophyta ii) Bryophyta iii) Pteridophyta iv) Angiosperms
v) Gymnosperms
Thallophyta :-
In this group the plants do not have well differentiated body parts.
The plants are called algae. They are mostly aquatic. Eg :- Spirogyra,
Ulothrix, Cladophora, Chara etc.
Spirogyra Ulothrix Chladophora Chara

16. Bryophyta :-
In this group the plant body is differentiated into stem and leaf like
structures but there are no specialised structures for the conduction of
water and other substances from one part of the plant body to the
other. These plants are called the amphibians of the plant kingdom.
Eg :- Moss (Funaria), Marchantia, Riccia etc.
Moss
Marchantia Riccia

17. Pteridophyta :-
In this group the plant body is differentiated into roots, stem and
leaves and has vascular tissue for conducting water and other
substances from one part of the plant body to the other. Eg :- Ferns,
Marsilea etc.
Ferns Marselia

18. Gymnosperms (Cryptogams) :-
The plants of this group bear naked seeds (gymno – means naked
and sperma means seed). They are usually perinneal, evergreen and
woody.
Eg :- Pines (Pinus), Cycas etc.
Pinus Cycas

19. Angiosperms (Phanerogams) :-
The plants of this group bears covered seeds (angio –
means covered and sperma – means seed). They are also
called flowering plants. The plant embryo in the seed have
cotyledons.
Angiosperms are divided into two groups on the basis of
the number of cotyledons. Plants with seeds having single
cotyledon are called monocots. Eg :- rice, wheat, maize etc.
green gram, peas, tamarind etc. Plants with seeds having
two cotyledons are called dicots. Eg :- green gram, peas,
tamarind etc.

20. Classification of plants
Plants
Do not have differentiated
body parts
Have differentiated
body parts
Thallophyta
Without vascular
tissue
Bryophyta
Bear naked seeds
Do not produce seeds
(Cryptogams)
Pteridophyta
Produce seeds
(Phanerogams)
Gymnosperms Angiosperms
Bear covered seeds
With vascular tissue
One cotyledon Two cotyledons
Monocots Dicots

21. Classification of animals (Animalia) :-
Animals are divided into ten groups. They
are :-
Porifera, Coelenterata, Platyhelminthes,
Nematoda, Annelida,
Arthropoda, Mollusca, Echinodermata,
Protochordata, and Vertebrata.

22. Porifera :- (Sponges)
• They are marine non motile
animals attached to some
soild support.
• They have pores all over
the body forming a canal
system which helps to
circulate water and bring food
and oxygen.
• They have a hard outer
skeleton and do not have any
tissues.
• Eg :-Spongila, Sycon,
Euplectelia etc.

23. Coelenterata
• They are aquatic animals.
• There is a cavity in the body
(coelom).
• The body has two layers of cells – an
outer layer and an inner layer.
• Some live in colonies (corals) and
others are single.
Eg :- Corals, Hydra, Jellyfish, Corals

24. Examples of coelenterata
Jellyfish
Sea anemone
Corals

25. Platyhelminthes :- (Flatworms)
1. They have three layers of cells and are called triploblastic.
2. They do not have true body cavity.
3. They may be free living or parasitic.
Eg :- Planaria (free living), Liverfluke, Tape worm (parasitic) etc.
1. They have flat body( dorsiventrally flattened) which is bilaterally
symmetrical. (Both right and left half of the body is similar.)
Planaria Liverfluke Tape worm

26. Nematoda :-
They have cylindrical body.
The body is bilaterally symmetrical and triploblastic.
They do not have true body cavity.( Pseudocoelome)
They have tissues but no real organs.
They are parasitic.
Eg :- Ascaris (round worms), Wuchereria ( Filarial
mworm) (pin worms) etc.
Filarial worm causes Elephentiasis
Ascaris
Wuchereria

27. Annelida :-
Their body is bilaterally symmetrical and triploblastic.
They have true body cavity.
Their body is segmented. ( Both internally & externally)
There is differentiation of organs.
They are found in water and on land.
Eg :- Earthworm, Nereis, Leech etc.
Earthworm Nereis Leech

28. Arthropoda
• Largest group of animal kingdom
• They have bilaterally symmetrical
body.
• The body is segmented.
• They have an open circulatory
system, The blood does not flow
in well defined open spaces
• The body cavity is filled with
blood.
• They have jointed legs.( Arthro-
Jointed legs )
• Eg :- Prawn, Crab, Cockroach,
Spider, Scorpion, Butterfly,
Housefly, Centipede etc.

29. Prawn
Crab
Spider Butterfly
Housefly
Cockroach Scorpion Centipede
Arthropoda Examples

30. Mollusca
• Second largest group in
animal kingdom
• They have bilateral symmetry.
• The coelomic cavity is
reduced.
• There is little segmentation.
• They have open circulatory
system and kidney like organs
for excretion.
• They have feet for moving
around.
• Eg :- Snails, Mussels, Chiton,
Octopus etc.

31. Snail (Pila)
Mussel (Unio)
Chiton
Octopus
Mollusca - examples

32. Mollusca - Examples

33. Echinodermata
• They are spiny skinned
organisms.
• They are free living marine
animals.
• They are triploblastic and have
coelomic cavity.
• The have water filled tube feet
which help in movement.
• They have hard skeleton made
of calcium carbonate.
• Eg :- Star fish, Sea urchin,
Feather star, Sea cucumber etc

35. Protochordata :-
They have bilateral symmetry and are tiploblastic.
The have coelomic cavity.
The have a notocord which is a long rod-like structure
along its back to which muscles are attached and help in
movement.
Eg :- Balanoglossus, Amphioxus, Herdemania etc.
Balanoglossus
Amphioxus
Herdemania

36. Vertebrata
• These animals have a true vertebral column and internal
skeleton, allowing a completely different distribution of
muscle attachment points to be used for movement.
Vertebrates are bilaterally symmetrical, triploblastic,
coelomic and segmented, with complex differentiation of
body tissues and organs. All chordates possess the
following features:
• (i) They have a notochord
• (ii) They have a dorsal nerve cord
• (iii) They are triploblastic
• (iv) They have paired gill pouches
• (v) They are coelomate.
•

37. Vertebrata :- (Vertebrates)
They have vertebral column and internal skeleton.
They have bilateral symmetry and are triploblastic.
They have coelomic cavity.
Their body is differentiated into tissues and organs.
Their body consists of four regions – head, neck, trunk
and tail.
They have two pairs of fins or limbs.
The respiration in aquatic forms is by gills and in land
forms respiration is by lungs
The sexes are separate.
Vertebrates are grouped into five classes. They are :-
Pisces, Amphibia, Reptilia, Aves and Mamalia.

39. Pisces
• They are fishes living in water.
• Their skin is covered with scales or
plates
• They respire using gills.
• They have streamlined body and fins
which help them to move in water.
• They are cold blooded and their heart
has only two chambers.
• They lay eggs from which the young
ones hatch out.
• Some fishes have skeleton made of
cartilage like Sharks, Rays etc. and
some have skeleton made of bones
and cartilage like Tuna, Rohu etc.

40. • Shark
Tuna
Electric ray Sting ray
Rohu
Pisces - Examples

41. Amphibia :- (Amphibians)
• They are found in land and water.
• They do not have scales but have mucous glands on their
skin.
• They are cold blooded
• Heart is three chambered.
• Respiration is through gills or lungs.
• They lay eggs in water.
Eg :- Frogs, Toads, Salamanders etc.
Frog Toad Salamander

42. Reptilia :-(Reptiles)
• They have scales
• Breathe through lungs.
• They are cold blooded.
• Most of them have three chambered heart but crocodiles have four
chambered heart.
• They lay eggs with hard covering in water.
Eg :- Snakes, Turtles, Lizards, Crocodiles etc.
Snake
Turtle
Lizard
Flying lizard
Crocodile

43. Aves :- (Birds)
•They are warm blooded animals.
•They have four chambered heart.
•They breathe through lungs.
•They have an outer covering of feathers.
•Their two fore limbs are modified into wings for flying.
•They lay eggs.
Eg :- Crow, sparrow, Pigeon, Duck, Stork, Ostrich
Crow
Sparrow
Pigeon
Duck
Stork
Ostrich

44. Mammalia :- (Mammals)
• They are warm blooded animals.
• They have four chambered heart.
• They have mammary glands for production of milk to nourish their young ones.
• The skin has hairs and sweat glands.
• Most of them give birth to their young ones. Some of them lay eggs (like Platypus and
Echidna).
Eg :- Cat, Rat, Dog, Lion, Tiger, Whale, Bat, Humans etc.

45. Nomenclature :-
All living organisms have been given scientific names
which can be used to identify them anywhere in the world.
The system of scientific naming organisms is called
binomial nomenclature. The binomial nomenclature
consists of two parts. The first part is the name of the
genus and the second part is the name of the species.
The system of scientific naming or nomenclature we use
today was introduced by Carolus Linnaeus.
Eg :- The scientific name of human beings is – Homo
sapiens.
Homo is the name of the genus and sapiens is the name of
the species.
Generic name starts with capital letter, specific name starts
with small letter