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Our Environment : NCERT Exercise Questions


Q.1      Which of the following groups contain only biodegradable items?
                    (a) Grass, flowers and leather     (b) Grass, wood and plastic
                    (c) Fruit peels, cake and lime      (d) Cake, wood and grass
Sol.         (a), (c) and (d)

Q.2      Which of the following constitute a food chain ?
                    (a) Grass, wheat and mango       (b) Grass, goat and human
                    (c) Goat, cow and elephant         (d) Grass, fish and goat
Sol.         (b) Grass, goat and human

Q.3      Which of the following are environment-friendly practices?
                    (a) Carrying cloth bags to put purchases in while shopping.
                    (b) Switching off unnecessary lights and fans.
                    (c) Walking to school instead of getting your mother to drop you on her scooter.
                    (d) All of the above.
Sol.         (d) All of the above.

Q.4      What will happen if we kill all the organisms in one trophic level?

If we kill all the organisms in one trophic level then transfer of food and energy to next level will stop.
For eg.
If,  in the above food chain, we kill the grasshoppers or Trophic level II organisms then transfer of energy from plants (Trophic level I) to snake (Trophic level III) will stop.

Q.5    Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?

(a) Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels.
For eg : -  Grass  \to Rabbit  \to Tiger :
In the above food chain : - 

(i) If we remove all the tigers at the third trophic level, then the number of rabbits will increase and these rabbits will eat up all the grass and plants  forest becomes desert.
(ii) If we remove all the rabbits at the second trophic level, then tigers will not get food and due to starvation they will die.
And, also the amount of grass and plants increase.

(b) No, all the organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

Q.6      What is biological magnification? Will the level of this magnification be different at different levels of the ecosystem?

When any harmful chemical like DDT enters in a food chain, its concentration increases gradually at each trophic level. This phenomenon is known as Biological magnification. Yes, the level of biological magnification is different for different levels. In trophic level I concentration of harmful chemical is less than other trophic level and in last trophic level concentration of harmful chemical is high.
For eg :-  Plant  \to   Goat  \to Man
In the above food chain, plants have minimum concentration of chemicals (Pesticides) and in Man , Concentration of chemical is high.

Q.7      What are the problems caused by the non-biodegradable wastes that we generate?

Non biodegradable wastes cause many problems like -
Enter in food chain and damage the organisms of highest trophic level.
Cause toxic effects to living organisms and may cause pollution like soil pollution, water pollution and air pollution in the environment.
Reduced crop yield.
Increase Biological oxygen demand.

Q.8      If all the waste we generate is biodegradable, will this have no impact on the environment ?

Even if all the waste we generate is biodegradable, it will have an impact on the environment. This is because too much biodegradable waste cannot be broken down into harmless simpler substances by the decomposers like micro-organisms at the right time. Due to this, the biodegradable wastes will go on accumulating in the environment and act as pollutants resulting in harmful effects on the environment. For example, the rotting biodegradable waste act as breeding grounds for flies and cockroaches, etc., which spread diseases. Moreover, the rotting biodegradable waste emit foul smell in the environment which makes the life of people miserable.

Q.9     Why is the damage to the ozone layer a cause for concern?What steps are being taken to limit this damage?

Ozone layer protects life on our earth from harmful rays (U.V. rays) of sun by absorbing these rays. Damage of Ozone layer leads to decrease in absorption of harmful rays of sun due to which these harmful rays reaches to earth's surface and cause harmful effects, so it is necessary to control this damage.
Steps being taken to limit this damage are -
To protect ozone layer, the United Nations environment program forged an agreement to freeze CFC production at 1986 levels.
Chlorofluoro carbons are now being replaced by hydro-fluorocarbons which do not damage the ozone layer.

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