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Ecosystems — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYEcosystems5 Marks
Question
  1. What is a trophic level in an ecosystem? What is ‘standing crop’ with reference to it?
  2. Explain the role of the ‘first trophic level’ in an ecosystem.
  3. How is the detritus food chain connected with the grazing food chain in a natural ecosystem?
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Answer

  1. Tropic level: 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 and this is known as trophic level.
Each trophic level has a certain mass of living material at a particular time and this is called as Standing crop. It is measured as the mass of living organisms (biomass) or the number in a unit area.
  1. First trophic level is formed by producers.
This is the basic unit.

These organisms can live without feeding on any another level.

The only thing that these organisms need to survive is sunlight and water which they can turn into energy themselves.

All other trophic levels depend on this level for energy.
  1. GFC is Grazing Food Chain: It is depicted as below:
Producers → Primary consumers → Secondary consumers

DFC is Detritus Food Chain: It begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms like fungi, bacteria etc.

GFC is the major conduct for energy flow. DFC may be connected with GFC at some levels: Some of the organisms of DFC are prey to the GFC animals.

$\text{Producers}\xrightarrow[]{\downarrow\ \text{Decomposers}}\ \text{Primary consumers}\xrightarrow[]{\downarrow\ \text{Decomposers}}\ \text{Secondary consumers.}$

These natural inter connection of food chains forms food web.

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