39. Why is energy flow considered as undirectional?

The flow of energy is unidirectional and non cyclic. The energy captured by the autotrophs does not return to the sun, and the energy which passes to the subsequent levels does not come back to autotrophs. The amount of energy goes on successively decreasing from the producers to the carnivores.


40. What is biomagnification? Will the level of this magnification be the different at different trophic levels?

Unknowingly some harmful chemicals enter our body through the food chain. These chemicals are either washed down into the soil and finally enter the water table or are taken up from the soil by the plants along with water and minerals and thus enter the food chain. As these chemicals are not degradable, these harmful chemicals get concentrated as biomagnification or biological magnification. The concentration increases in successive trophic levels.


41. Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment.

The living organisms which decompose or consume the dead remains of other organisms are called decomposers.

Certain bacteria and fungi break down the complex organic compounds present in the dead organisms into simpler substances. So they are called decomposers.

Advantages of decomposers

(i) by decomposing the dead organisms, the decomposers clean the decomposed elements enter the soil, this maintains its fertility.


42. What are the three major types of pollution? Name two pollutants in each category.

Three major types of pollution and their pollutants are

Air Pollution - Pollutants 1. Ash from smoking volcanoes
2. Gases such as CO2, CH4, produced by burning of fossil fuels.
Water Pollution - Pollutants 1. Detergents
2. Industrial wastes
Land Pollution - Pollutants 1. Pesticides
2. Garbage.

43. Distinguish between ‘ conservation’ and ‘ preservation’. Suggest any four practices which may help in protecting our environment.

Conservation is the sensible use of the earth's natural resources in order to avoid excessive degradation while ‘preservation’ is to keep something in order to prevent it from decaying or being destroyed.

Practices for protecting our environment

(i) Undertaking crop rotation.
(ii) Judicious use of fertilizers.
(iii) Treatment of sewage.
(iv) Planting of trees.