CBSE Questions for Class 10 Biology Our Environment Quiz 6 - MCQExams.com

Decomposers recycle the nutrients in an ecosystem. Bacteria and fungi act as major decomposers feed on organic matter present in the dead bodies of animals and plants. Decomposers in turn break down the organic matter present in the dead animals to simple nutrients in the soil. This organic matter is used by plants to grow.

Thus, the correct answer is option D.

• In all the ecosystems there is an interaction between the living organisms and their physical environment. 
• Here, all the living organisms are the biotic components, whereas the physical environment forms the abiotic components.

• Wastes can be distinguished as decomposable waste and non-decomposable waste. 
• Products that can be easily broken down naturally by water, air, solar energy or microorganisms are termed decomposable wastes.
• Products that cannot be decomposed or dissolved by natural agents are termed non-decomposable waste. 
• Ash is decomposable while thermocol, plastic bags, resins are non-decomposable.  

• The organisms which cannot produce food by themselves and depend on producers are known as consumers. 
• With the increase in the trophic levels, the energy goes on decreasing as there is a loss of energy during the transfer at each step. This is the reason that the lower trophic levels have more energy when compared to the higher trophic levels. 
• Many food chains are interconnected in the food web and so one organism may be associated with more than one food chain. The same organism may feed or be eaten by one or more organisms. 
• The producers capture the radiant energy of the sun and prepare their food. This food is consumed by consumers. When a plant or an animal dies, its dead remains are broken down into simpler inorganic compounds by decomposers. Decomposers derive nutrition from the dead decaying matter.

• Food chain in an ecosystem is defined as the passage of food from one trophic level to the next higher trophic level. 
• A food chain can have 3 or 4 trophic levels. 
• Plants are producers which are present in first trophic level. 
• Primary consumers are second trophic levels which eat plants. They are herbivores. 
• Secondary consumer are present make third trophic level. They eat primary consumers and are carnivores. 
• Tertiary or top consumer make fourth trophic level. They are carnivores
• Thus, the correct answer is option A- 'Three or four.'