Page No. 257
1. Why are some substances biodegradable and some non-biodegradable?
Ans: Substances which can be broken down with the help of enzymes secreted by the bacteria and other saprophytes over a period of time are biodegradable. These substances have short molecular organisation and can be assimilated by the saprophytes. Non-biodegradable substances cannot be acted upon by the enzymes in nature as they consist of polymers which are strongly bonded with each other.
2. Give any two ways in which biodegradable substances would affect the environment.
Ans:
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Biodegradable substances in large quantities would contribute to the pollution of the environment and
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They serve as a breeding ground for flies which are carriers of many diseases such as malaria, cholera, etc.,
3. Give any two ways in which non-biodegradable substances would affect the environment.
Ans:
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The non-biodegradable substances get accumulated and don’t get decomposed hence it remains in the ecosystem and causes pollution, chokes the system of many animals and kill them.
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These substances due to accumulation cause water and soil pollution e.g., pesticides, detergents, polythene.
Page No. 161
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Ans: Trophic level is the functional level occupied by an organism in a food chain. Trophic literally means feeding, so trophic levels are the positions at which species feed. Examples: A simple herbivorous food chain where; maize occupies first trophic level, Locust occupies second trophic level, lizard occupies third trophic level and a snake occupies fourth trophic level. Producers (maize) always occupies the first trophic level, whereas primary consumers (locust) occupies 2nd trophic level, secondary consumer occupies 3rd trophic level and the tertiary consumer occupies 4th trophic level.
2. What is the role of decomposers in the ecosystem?
Ans: Various roles played by decomposers in the ecosystem are:
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They decompose biodegradable substances into useful substances.
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They release nutrients into the soil by decomposing dead and decaying matter, thus making the soil fertile.
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They maintain the nutrient pool by returning back the nutrients in the pool.