Biology - Our Environment


  • Environment is a natural world in which all living beings and non-living things exist.

  • The substances, which are broken down by the biological processes, are known as biodegradable.

  • The substances, which are NOT broken down by the biological processes, are known as non-biodegradable.



  • An ecosystem comprises of biotic components (all living organisms) and abiotic components (all physical factors, such as temperature, rainfall, wind, soil and minerals) of a given area. E.g. Lake ecosystem, Forest ecosystem, Marine ecosystem, etc.

  • In a given geographic region, all the living organisms interact with each other and their growth, reproduction, and other activities are largely dependent on the abiotic components of the ecosystem.

  • In an ecosystem, all green plants and certain blue-green algae can produce their food (themselves) by the process of photosynthesis; hence, they are known as the producers.

  • The organisms, depending on the producers either directly or indirectly, can be termed as herbivores, carnivores, omnivores and parasites.

  • All those animals that eat plants are known as herbivores (also known as primary consumers). E.g. cow, goat, rabbit, deer, etc.

  • All those animals that eat other animals are known as carnivores (also known as secondary consumers) E.g. tiger, lion, snake, etc.

  • All those animals that eat both plants (and its products) and other animals are known as omnivores.

  • The larger size of carnivores and omnivores animals are known as tertiary consumers.

  • The microorganisms, such as bacteria and fungi, break-down the dead remains and waste products of organisms and hence they are known as decomposers.

  • The pyramid given above illustrates that the population of producers is maximum and as we go up, the population of subsequent consumers keeps decreasing.

Food Chain

  • A series of animals (of different biotic level) feeding one another forms a food chain.

  • Each level of the food chain forms a trophic level (see the image given below).

Food Chain
  • In the given image, (a) illustrates food chain in nature; (b) illustrates food chain in a grassland region; and (c) illustrates food chain of pond ecosystem.

  • The autotrophs (i.e. producers) exist at the first trophic level.

  • The herbivores (i.e. the primary consumers) come at the second trophic level.

  • The small carnivores (i.e. the secondary consumers) comes at the third trophic level and larger carnivores or the tertiary consumers comes at the fourth trophic level.

Transmission of Energy

  • While transmission of energy from one trophic level to second, large amount of energy gets lost, which cannot be used again.

  • The green plants (i.e. producers) in a terrestrial ecosystem capture about 1% of the energy of sunlight and convert it into food energy.

  • Secondly, when primary consumers eat green plants, about 10% of the food eaten is transmitted into its own body and made available for the next level of consumers.

Food Web

  • When the (food) relationship is shown in a series of branching lines instead of a straight line, it is known as a food web (see the image given below).

Food Web