Science: Natural Environment: Components of Ecosystem and Biotic Community (For CBSE, ICSE, IAS, NET, NRA 2022)

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An ecosystem may be defined as “a biological environment consisting of all organisms living in a particular area, as well as the non-living physical components of the environment with which the organisms interact” . An ecosystem can either be natural or human-designed. All ecosystems that exist in nature are Natural ecosystem. They can either be terrestrial or aquatic. Grasslands and deserts constitute the terrestrial ecosystem while rivers, ponds and oceans form the aquatic ecosystem. On the other hand, man-made or human designed ecosystem is an artificial ecosystem e. g. gardens, aquarium, crop fields etc.

Components of Ecosystem

  • Abiotic: Abiotic components are the non-living physical and chemical factors in the environment of an ecosystem.
  • Biotic: Biotic components are the organisms which include plants, animals and micro-organisms in an ecosystem.
Components of Ecosystem

Biotic Community

Biotic community refers to populations of various kinds of organisms living together and sharing the same habitat. Depending on the mode of nutrition, members of a biotic community are categorized into autotrophs, heterotrophs and saprotrophs.


  • All plants (except for a few parasitic plants) can manufacture their own food by the process of photosynthesis, organisms that can manufacture their food by the process of chemosynthesis. So, species that produce their own food on their own are called autotrophs. Autotrophs form the basis of any biotic system as they trap solar energy to manufacture food for all.
  • In terrestrial ecosystems, the autotrophs are mainly the rooted plants while in aquatic ecosystem, floating plants called phytoplankton and shallow water rooted plants called macrophytes are the examples of autotrophs.
  • Heterotrophs (Gr: heteros - other; trophos - feeder) are called consumers which feed on plants and animals. Consumers include herbivores (that eat plant material) and carnivores (which eat other animals) .
  • Saprotrophs (Gr: sapros - rotten; trophos - feeder) also called decomposers are feed on dead and decaying matter. They break down the complex organic compounds of dead plants and animals into simpler forms and return them back into the environment. Decomposers form an important link between the living and non-living component of the ecosystem. Some bacteria and fungi belong to this category
Biotic Community: Autotrophs

Food Chain

  • food chain may be defined as “succession of organisms in an ecological community that constitutes a passing on of food energy from one organism to another as each consumes a lower member and in turn is preyed upon by a higher member of the food chain.”
  • A simple food chain basically consists of producers, herbivores and carnivores. Just like the pond, a simple food chain in a terrestrial ecosystem links the trees and shrubs (producers) , the giraffes (herbivores that eat trees and shrubs) and the lions (carnivores that eat the herbivores) .

Types of Food Chain

Grazing Food Chain

Grazing food chain is found both in aquatic as well as grassland ecosystem. It is the most common food chain found in the terrestrial ecosystem.

Detritus Food Chain

This type of food chain starts from dead organic matter. The dead organic matter is broken down into simple nutrients by micro-organisms like fungi and bacteria. These simple nutrients and decomposers are then consumed by smaller carnivores which in turn become food for larger carnivores.

Detritus Food Chain

Energy Flow in an Ecosystem

  • Food provides energy and thus in a food chain, energy is passed from one link to another. This energy flow is unidirectional i.e.. the energy which is transferred from one trophic level to the next does not come back.
  • When an herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as heat or is used up by the herbivore to carry out its life processes (e. g. , movement, digestion, respiration, reproduction) .
  • Therefore, when the herbivore is eaten by a carnivore, only a small amount of total energy is received by the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be lost as heat or “used up” by the carnivore. The carnivore then has to eat many herbivores to get enough energy to grow. Because of the large amount of energy that is lost at each link, the amount of energy that is transferred gets lesser and lesser as we go up the food chain.

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