Question

[5]
(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 ?

Answer 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. [1]

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. [1]

[2]
(b) The most important trophic level within the ecosystem is the first level: primary producers. These organisms live without feeding off another level. They only need sunlight and water to survive. The 'first trophic level' in an ecosystem plays very important role in an ecosystem :
(i) The first trophic level has producers or autotrophs which trap solar energy to produce food for other trophic levels by photosynthesis.
(ii) Organic compounds formed in this process are essential in the process of building of bodies and also help in releasing energy.

(c) Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of detritus food chain are prey to the grazing food chain animals in a natural ecosystem. We observe that in a natural ecosystem few animals like cockroaches and crows are omnivores. These natural interconnections of food chains make it a food web. [1]