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Our Environment

Our Environment Synopsis

Synopsis

 

Ecosystem

  • The term ecosystem was coined by Tansley. According to him, ‘ecosystem is a symbol of structure and function of nature’.
  • The term ecology was coined by Reiter. 
  • The term ecology was first described Ernst Haeckel.
  • Prof. Ramdas Mishra is regarded as the Father of India Ecology.
  • The total group of living things and environment of factors present in a particular place is called an ecosystem.
  • Larger ecosystems are called biomes.
  • A science of self-control [homeostasis] in an ecosystem is called cybernetics.

Types of Ecosystem

 

Components of an Ecosystem

  • An ecosystem consists of two main components: biotic components and abiotic components.




 

Structure of an Ecosystem

 

 

Functions of an Ecosystem

 

 

 

 

Food Chain

  • The sequential process of eating and being eaten is called a food chain.
  • All food chains begin with green plants or the producers. So, the plants or the producers constitute the first trophic level. Example: Grass
  • The herbivores or primary consumers which feed on plants constitute the second trophic level. Example: Grasshopper
  • The herbivores are next fed upon by the carnivores or secondary consumers. They constitute the third trophic level. Example: Snake
  • Finally, the large carnivores, also called the top carnivores or tertiary consumers form the fourth trophic level. Example: Hawk
  • The large carnivores die and form the feed of the decomposers. The decomposers feed on these dead animals and plants. Example: Fungi
  • There is transfer of food from one organism to the other forming a chain.
  • A food chain represents unidirectional transfer of energy.



 
Examples of Short Food Chains
  • Rice → Man   (Two steps)
  • Grass → Rabbit → Fox (Three steps)
  • Maize → Goat → Man (Three steps)
 
Examples of Long Food Chains
  • Grass → Grasshopper → Lizard → Crow (Four steps)
  • Algae → Protozoa → Small fish → Large fish (Four steps)
  • Green plant → Grasshopper → Frog → Snake → Eagle (Five steps)
 
 
Types of Food Chains
 
 
 
Energy Flow in a Food Chain
  • In a food chain, along with food, transfer of energy also occurs from one trophic level to the other. The flow of energy which occurs along a food chain is called energy flow.
  • All living organisms in an ecosystem require energy for carrying out various life processes such as breathing, growth and movement. This energy supports various activities of the living world.
  • All the energy used by living organisms is obtained from the Sun. Solar energy enters the living components through the autotrophs or green plants, where it gets converted into chemical energy. However, only 1% of the total energy is actually captured by green plants. 
  • The food energy produced by plants is partially used by them for their growth and development. A major part of it is lost as heat energy.
  • The plants are then eaten by primary consumers, the herbivores, and the energy stored in plants is transferred to these organisms. A part of the energy is used by herbivores for activities such as digestion, growth and reproduction. Again, most of the energy is lost to the environment in the form of heat.
  • When herbivores are consumed by carnivores, a part of the energy is used by the carnivores for their metabolic activities and growth, while most of it is released as heat energy.
  • The amount of energy gradually declines as one move up to each higher trophic level, because at each level, energy is lost in the form of heat.



  • Due to the loss of energy at each step, food chains consist of only three to four trophic levels. If there are many levels, then animals at the end of the food chain will not have enough food and energy to survive. The solar energy converted by the autotrophs into food energy cannot be reconverted into solar energy, and the energy which passes from the herbivores to the carnivores can never go back to the herbivores. The energy lost as heat cannot be returned to the plants and reused during photosynthesis. Therefore, the flow of energy through a food chain is always unidirectional. 

Food Web                                                          

  • Similar kinds of organisms may occur in more than one food chain. They eat more than one type of food to satisfy their requirements. A plant of a particular species can serve as food for a variety of herbivores. 
  • No food chain can operate in isolation. Individual food chains are interconnected in a complex way. 
  • A network of interconnecting food chains in a natural community of different organisms is called a food web.

Example of Food Web

  • Consider six food chains which are interconnected to form a food web. The food web begins with plants and ends with the top carnivore, the vulture.
  • In the first food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten by the vulture.
    Plants → Grasshopper → Vulture
  • In the second food chain, the plants are eaten by the rabbit. The rabbit is then consumed by the vulture.
    Plants → Rabbit → Vulture
  • In the third food chain, the plants are eaten by the rat. The rat is then eaten by the vulture.
    Plants → Rat → Vulture
  • In the fourth food chain, the plants are eaten by the rat, the rat is eaten by the snake, and the snake, in turn, is eaten by the vulture.
    Plants → Rat → Snake → Vulture
  • In the fifth food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten by the frog. The frog is eaten by the snake, and the snake is consumed by the vulture.
    Plants → Grasshopper → Frog → Snake → Vulture
  • Finally, in the sixth food chain, the plants are eaten by small birds which in turn are eaten by the vulture.
    Plants → Small birds → Vulture