NCERT Solutions for Class 10 Science Chapter 15 Our Environment

Ans : Trophic Levels : The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. Example A food chain operating in a grassland is given below :
Grass -> Insects -> Frog->  Birds



In this food chain
1. Grass represents first trophic level.
2 Grasshopper represents second trophic level.
3. Frog represents third trophic level.
4 Eagle represents fourth tropic level. 

Ans : (i) Decomposers help in decomposing the dead bodies of plants and animals and hence act as cleansing agents of the environment.
(ii) Decomposers also help in putting back the various elements of which dead plants and animals are made, back into the soil, air and water for reuse by the producers like crop plants.
(iii) They help in recycling of the nutrients.
(iv) They decompose dead remains thereby providing space for new life to settle in the biosphere. 

Ans : The microorganism like bacteria and other decomposer organisms (called saprophytes) present In our environment are specific in their action. They break down the materials or products made from natural materials (say, paper) but do not break down man-made materials such as plastics. So, it is due to the property of decomposer organisms of being specific in their action that some waste materials are biodegradable, whereas others are non-biodegradable. 

Ans : (i) Biodegradable substances are decomposed by the action of microorganisms and decomposed materials are recycled through geo-chemical cycle.
(ii) These substances keep the environment clean. 

Ans : (i) They cause air, water and soil pollution.
(ii) They may cause bio-magnification in the food chain and end up in humans.