All the organisms such as plants, animals, microorganism, and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form the ecosystem.

Thus, an ecosystem consists of biotic components (living organisms) and abiotic components (physical factors like temperature, rainfall, wind, soil, and minerals).

Organisms can be grouped as producers, consumers, and decomposers according to how they obtain their food from the environment.

• All green plants and some blue-green algae which can produce food by photosynthesis come under this class and are called producers.

• Organisms that consume the food produced either from producers or indirectly by feeding on others are the consumers (herbivores, carnivores, omnivores, and parasites).

• The microorganisms, comprising bacteria and fungi, break down the dead remains and waste products of organisms, these microorganisms are decomposers.

The constituents of the ecosystem are seen to function as a unit when you consider –

1. Productivity

2. Decomposition

3. Energy flow

4. Nutrient cycling


• PRODUCTIVITY – A regular input of solar energy is the basic requirement for any ecosystem to function and sustain.

Primary productivity – Amount of biomass produced per unit area over a while by plants during photosynthesis.

The rate of biomass production is called productivity. It can be divided into GROSS PRIMARY PRODUCTIVITY(GPP) and NET PRIMARY PRODUCTIVITY(NPP).

GPP of a system is the rate of production of organic matter during photosynthesis. Whereas, NPP is GPP – R (Respiration loss).


Secondary productivity – Rate of production of new organic matter by consumers.


• DECOMPOSITION – Decomposer breakdowns complex organic matter into inorganic substances, this process is known as decomposition. The main steps in decomposition are fragmentation, leaching, catabolism, humification, and mineralization.

– Break down of detritus(materials) into small particles is called fragmentation.

– Water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts this process is known as leaching.

– Bacterial and fungal enzymes degrade detritus into simpler inorganic substances, this process is known as catabolism.

– Accumulation of dark-colored amorphous substance called humus is called humification.

– The hummus is further degraded by some microorganisms, and the release of inorganic nutrients occurs through mineralization.


• ENERGY FLOW – Sun is the only source of energy for all the ecosystems on earth, Of the incident solar radiation lea than 50% of it is photosynthetically active radiation (PAR). Plants capture only 2-10% of the PAR and a thus small amount of energy sustains the entire living world.

This is passed from the first trophic level to the last level. Thus, formed a series of organisms feeding on one another, this series of organisms taking part at various biotic levels form a food chain.

– The autotrophs or the producers are the first trophic level, they fix up the solar energy and make it available for heterotrophs or consumers.







If the food chain’s complexity increases then, instead of a straight-line food chain, the relationship can be shown as a series of branching called a food web.


• NUTRIENT CYCLING – The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling.

These are of 2 types –

1. Gaseous (Nitrogen and Carbon cycle)

2. Sedimentary (Sulphur and Phosphorous cycle)

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