The sum total of organism, environment & the interaction between them is called the Ecosystem. The term was coined by Sir Arthur Tansley in 1935 which was later defined by Eugene P.Odum in 1940 as the basic unit of ecology.

Components of Ecosystem

1) Biotic or living components :

It includes all kinds of organisms;plants,animals or microorganisms.

2) Abiotic or Non-living components :

These components are non-living & include climatic factors like light,temperature,humidity & wind & environmental factors like air,soil & water. However,environment has been modified by human beings according to their needs & advancements. These modifications of environment constitute cultural components.

Biotic components

The biotic components are classified into 3 types based on their nutritional relationship.

a) Plants (Producers) :

These components trap solar energy,& manufacture their own food & are also known as Autotrophs.These include green plants,trees,grass etc…

b) Animals (Consumers) :

These organisms unable to synthesize food.They depend on producers for their nutrition & are also called Heterotrophs.Consumers are classified into following types based on the food consumed.
Primary consumers :These organisms eat the plant or plant parts are called herbivores.Examples are Rabbit,deer,pigeon,grasshopper etc…
Secondary consumers :Also called carnivores,they feed on herbivores.These includes lizards,snakes,tiger,wolf etc…
Tertiary consumers :These are also called carnivores which feed upon secondary consumers.Example,peacock is a tertiary consumer which feeds upon snakes( Secondary consumer) which eats rats(primary consumer).


These heterotrophs are called saprotrophs,feed on dead & decaying organic matter.They break down complex organic compounds,absorb some of the products & release remaining nutrients in the environment.Reducers include microorganisms such as bacteria & fungi.

Food chain:

The sequence of organisms with repeated eating or being eaten is known as food chain.However,each chain is made up of certain levels, the basic features of which are same.Each level is known as trophic level.
1) First trophic level : The plants are producers & synthesize food for other organisms.Therefore, they always occupy the first trophic level.
2) Second trophic level : It is occupied by Herbivores.
3) Third trophic level: The primary carnivores feeding upon herbivores from the third trophic level.
4) Fourth trophic level: The bigger carnivores which eat upon small carnivores form the fourth trophic level & so on.

Food Web :

Food chain interconnected with each other forming a Food -Web.
1) grass -> grasshopper -> hawk
2) grass -> grasshopper -> lizard -> hawk
3) grass -> rabbit -> hawk
4) grass -> mouse -> hawk
5) grass -> mouse -> snake -> hawk
From above it is seen that same organisms are present in diffrent food chains at different tropic levels.