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(a) What is a trophic level in an ecosystem ? What is ‘standing crop’ with reference to it ?

(b) Explain the role of the ‘first trophic level’ in an ecosystem.  

(c) How is the detritus food chain connected with the grazing food chain in a natural ecosystem ? 

 

 

 

 
 
 
 
 

Answers (1)

a) Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third.

Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight.

b) The most important trophic level within the ecosystem is the first level: primary producers. These organisms live without feeding on another level. They only need sunlight and water to survive. They convert solar energy into food. All other organisms depend on these primary producers to obtain their nutrition.

c) The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs. Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them. In an aquatic ecosystem, Grazing food chain (GFC) is the major conduit for energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC. Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of DFC are prey to the GFC animals, and in a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores. These natural interconnection of food chains make it a food web.

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Priyanka Kumari

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