Our Environment

NCERT SOLUTIONS

Our Environment
 Our Environment

IN CHAPTER QUESTIONS

PART - 1

Q1. Why are some substances biodegradable and some non-biodegradable?

S.No. Biodegr adable Waste Non-biodegr adable wast e

1 . They can be broken down into They can't be broken down into
simpler substances by the activity simpler and harmless products
of biological catalysts called because the biological catalysts
enzymes (present in surrounding called enzymes can't act upon
bacteria or other saprophytes). them. They can be acted upon
Physical processes like heat and only by some physical processes
temperature help in the like heat and pressure.
functioning of enzymes.
2 . They can enter the They cannot enter the
biogeochemical cycles. biogeochemical cycles.
3 . They become pollutants only They always act as pollutants
when they accumulate in large whether present in small or large
quantities and not degraded at quantity.
the right time.
4 . All the biodegradable wastes They can't be treated properly
should be treated properly before before discharging them into
Ans.
discharging them into water or water or soil. Instead, they can be
soil. either recycled or reused.
5 . They do not persist in the They persist in the environment
environment for a long time. for a long time.
6 . Examples : Urine and faecal Exam ples : Heavy metals like
matter, Sewage, Paper, Mercury, Lead, Arsenic,
Vegetable and fruit peels, Radioactive wastes like Uranium,
Agricultural residues, Wood and Plutonium, Insecticides and
Cloth. Pesticides like DDT and BHC.

Q2. Give any two ways in which biodegradable substances would affect the environment.

Ans. (i) If biodegradable substances are not degraded properly on right time , They will be
accumulated and will act as pollutant.
(ii) They are used in composting which forms humus that enhances soil fertility.

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Q3. Give any two ways in which non-biodegradable substances would affect the environment.

Ans. (i) Non-biodegradable substances contaminate soil and water resources as they cannot be
decomposed.
(ii) They may be radioactively active which have hazardous effects to human beings.

PART - 2

Q1. What are trophic levels? Give an example of a food chain and state thedifferent trophic
levels in it.

Ans. Trophic levels : The distinct sequential steps in the food chain where transfer of energy occurs
are referred to as different trophic levels.

Grass Deer (Herbivore) Lion

(Autotrophs) (Carnivore)

Bacteria and Fungi

(Decomposers)

Fig.2 A simple food chain

Q2. What is the role of decomposers in the ecosystem?

Ans. Decomposers are essential components of ecosystem. They decompose dead remains of plants
and animals and their waste organic products into simpler, inorganic substances. The latter are
released into the environment for their reuse as raw materials by the producers. Thus it maintains
balance in nature and play important role in ecosystem.

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PART - 3

Q1. What is ozone and how does it affect any ecosystem?

Ans. (i) Ozone is formed in atmosphere by the action of ultraviolet radiation on oxygen gas.
(ii) The high energy ultraviolet radiation (UV radiation) coming from the sun splits oxygen gas
into free oxygen atoms
Ultraviolet
O2   2O (oxygen atom)
radiations from sun
(iii) The free oxygen atoms are highly reactive. One oxygen atom reacts with an oxygen molecule
to form an ozone molecule.
O2 + O  O3 (Ozone molecule)

Q2. How can you help idegradable and non biodegradable waste before dumping

Ans. To reduce the problem of waste disposal we can :-

(i) Segregate the biodegradable and non biodegradable waste before dumping
(ii) Remove all materials which can be recycled. eg paper, glass.

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EXERCISES
Q1. 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-juice
(d) Cake, wood and grass

Ans. (c) Fruit-peels, cake and lime-juice

(d) Cake, wood and grass

Q2. Which of the following constitute food-chain ?

(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat.

Ans. (b) Grass, goat and human.

Q3. 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.

Ans. (d) All of the above.

Q4. What will happen if we kill all the organisms in one trophic level ?

Ans. If we kill all the organisms in one trophic level then transfer of energy as well as matter to next
higher level will stop. It will lead to over population at lower trophic level causing competition
amongst the individuals. This would seriously disturb the food chain and can cause even a collapse
of an ecosystem.

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Q5. 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 ?

Ans. Yes, the impact of removing all the organisms in a trophic level will be different for different
trophic levels.
For example : Consider the following food chain: Plants  Deer  Lion.
If all the lions are removed then the population of deer will increase to such a larger extent and
this may result in the following problems:
(i) Due to over-grazing caused by deers soil erosion can take place and forest area will get affected.
(ii) Due to large deer population competition for food will start.
Similarly, if deers are removed then carnivores will get affected. Whereas removal of producers
(plants) will affect both deers and lions.
This all suggests that all different organisms in a food chain are linked together and removal
of any organism will have different effect but it will cause an ill effect on the stability of that
ecosystem.

Q6. What is biological magnification ? Will the levels of this magnification be different at different
levels of the ecosystem ?

Ans. The accumulation of harmful chemicals in the body of living organisms at different trophic levels
in a food chain is called biological magnification. Yes, the concentration of these harmful chemicals
will be different at different trophic levels. It will be maximum at the last trophic levels which
is mostly of the top carnivores (quaternary consumers).

Q7. What are the problems caused by the non-biodegradable wastes that we generate ?

Ans. (i) Non-biodegradable waste persist in the environment for a long time and cause greater harm
to the various members of the ecosystem by causing biological magnification.
(ii) Non-biodegradable waste such as fertilizers, pesticides, weedicides, etc., changes the soil
chemistry. This inturn affects the fertility of soil and subsequently reduces the crop yield.

Q8. If all the waste we generate is biodegradable, will this have no impact on the environment ?

Ans. Biodegradable waste will be recycled easily by the decomposers such as bacteria and fungi. It
will have only this bad impact on our environment that, many of the gases released during
decomposition process may result in global warming.

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Q9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Ans. The ozone shields the surface of the earth from ultraviolet (UV) radiation from the sun. These
radiations are highly damaging as they can cause cancer in both plants and animals, damage
to eyes and immune system.
They can also lead to variations in global rainfall, ecological disturbances and dwindling of global
food supplies.
Due to these reasons, damage to the ozone layer is a major cause for concern.
Steps which are taken to limit this damage:
(i) To decrease the use of synthetic chemicals like chloro fluorocarbons (CFCs) which are used
as refrigerants and in fire extinguishers.
(ii) In 1987, the United Nations Environment Programme (UNEP) succeeded in reaching an
agreement to freeze CFC production at 1986 levels.