Food Chain & Food Web - Practice Questions & MCQ

Trophic Level:

• The producers and consumers in the ecosystem can be arranged into several feeding groups, each known as trophic level (feeding level). 
• In any ecosystem: 
  • producers represent the first trophic level, 
  • herbivores present the second trophic level, 
  • primary carnivores represent the third trophic level and 
  • top carnivores represent the last level

Food Chain:

• In the ecosystem, green plants alone are able to trap in solar energy and convert it into chemical energy. 
• The chemical energy is locked up in the various organic compounds, such as carbohydrates, fats and proteins, present in the green plants. 
• Since virtually all other living organisms depend upon green plants for their energy, the efficiency of plants in any given area in capturing solar energy sets the upper limit to long-term energy flow and biological activity in the community.
• A food chain may be defined as the transfer of energy and nutrients through a succession of organisms through repeated processes of eating and being eaten. 
• In the food chain the initial link is a green plant or producer which produces chemical energy available to consumers. 
• For example, marsh grass is consumed by grasshoppers, the grasshopper is consumed by a bird and that bird is consumed by hawks.
• The above example can be represented as:

               Marsh grass → grasshopper → bird → hawk
 
Food Web:

• In reality, a species of a specific trophic level is dependent on several species belonging to different trophic levels for its nourishment. 
• Because of such food habits, a complex relation exists between the different species as consumer and consumed.
• These natural interconnections of food chains make it a food web. 

Detritus Food Chain:

• 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 (sapro: to decompose).
• Decomposers secrete digestive enzymes that break down dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them.

Grass Food Chain:

• In an aquatic ecosystem, 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.