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Our Environment : NCERT Intext Questions


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Page 257, Page 261, Page 264,

Page 257

Q.1      Why are some substances biodegradable and some non-biodegradable?


Biodegradable substances are those substances on which micro-organisms like bacteria or decomposers act and break down these substances into simpler compounds, example of Biodegradable substances are dead remains of plants and animals and their waste products, paper etc.
But on some compounds like plastics and metals, micro-organisms do not act to decompose them and these compounds are known as non-biodegradable compounds.

Q.2      Give any two ways in which biodegradable substances would affect the environment.

Biodegradable substances would affect the environment in following two ways-
(i) These substances decomposed by the action of micro-organisms that cause foul smell.
(ii) The rotting biodegradable wastes act as breeding ground for insects which may cause diseases to living organisms.

Q.3      Give any two ways in which non-biodegradable substances would affect the environment.

Non-biodegradable substances would affect the environment in following two ways-
(i) Non- biodegradable substances may cause soil pollution and water pollution.
(ii) If non-biodegradable substances remain in fertile soil or land than it becomes barren.

Page 261
Q.1      What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Trophic levels - The flow of food or energy in an ecosystem is called food chain.
Those organisms which join the food chain are termed as trophic levels
There are four trophic levels:
(i) First trophic level - Producers (Plants)
(ii) Second trophic level – Primary consumers.
(iii) Third trophic level - Secondary consumers.
(iv) Fourth trophic level - Top consumers.
formatIn the above food chain plants are producers and represents the first trophic level.

Rabbit is the primary consumer i.e. herbivorous animal and represent the second Trophic level.
Wolf is the secondary consumer and represents the third trophic level.
Tiger is the top consumer and represents the fourth trophic level.

Q.2      What is the role of decomposers in the ecosystem?

Decomposers act as cleansing agents of environment as they decompose the dead bodies and dead parts of plants and animals and clean the environment.

Page 264
Q.1      What is ozone and how does it affect any ecosystem?

Ozone is a gas made up of three atoms of oxygen joined together. i.e.O3.
Between 20 – 26 km above the sea level, ozone forms a layer known as ozone layer.
This ozone layer absorbs the harmful U.V. radiations of the sunlight and hence, protects the earth and living organisms from the harmful effects of U.V. rays.
So, this layer is very important for the survival and existence of life on earth. Thus, it protects the ecosystem.

Q.2      How can you help in reducing the problem of waste disposal? Give any two methods.

(i) We should use more and more substances that leave biodegradable wastes.
(ii) We should reduce the use of non-biodegradable wastes like plastics or recycle them.



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