A natural unit comprising of living and non-living components, interacting and exchanging materials between them forms a self-dependent and adaptable system known as ecological system or ecosystem. 

The main components of an ecosystem can be classified as: 

(i) Biotic: Includes all the living organisms. 

(ii) Abiotic: Includes all the nonliving components of an ecosystem. 

(iii) Biotic component: These are as follows. 

(a) Producers: These are the green plants which trap solar and convert it to potential chemical energy. These are also known as autotrophs. 

(b) Consumers: All animals and non-green plants which directly or indirectly depend upon the producers for energy from the food. 

(c) Decomposers: These include all micro-organisms which cause decomposition of the dead remains of the plants and animals and utilise a part of the product of decomposition and release the rest of it for use by the producers. Here the decomposers decomposes organic substances to simpler inorganic form. 

(ii) Abiotic factors: The major abiotic factors of an ecosystem includes air, water, soil, light, temperature. 

(a) Air: Air is essential part of an ecosystem. Air means O₂ CO₂, N₂ and other essential components for life. Air should be pure. 

(b) Water: Water is the major constituent of supporter of protoplasm and in an ecosystem water may be present in liquid, vapour and in solid form.

 (c) Light: Light is another limiting factor of an ecosystem. It is essential for the growth, development and for the distribution of some animals and plants. 

(d) Temperature: It is also most essential regulating factor for plants and animals in an ecosystem.