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1. CHAPTER – 15
OUR ENVIRONMENT

2. Introduction
We have the word
environment often being
used on the television, in
newspapers and by people
around us. Environment (F.
environ – about ) is the
sum total of all external
factors, substances, living

3. beings, and conditions that
surround an organism and
influence the same without
becoming its part. It
consists of both living and
non- living components,
each of which has several
sub-components which are
interlinked and

4. interdependent on each
other. In this chapter, we
shall be studying how
various factors in the
environment interact with
each other and how we
impact the environment.

5. Sub-Concept 15.1
What happens when we
add our waste to the
environment?

6. Effect of adding waste to
the environment
Human activities produce
a lot of waste materials
which are thrown away
into the environment.
These wastes cause

7. pollution of air, water
and soil. The waste
materials produced are
of two main types. They
are biodegradable
wastes and non
biodegradable wastes.

8. i)Biodegradable wastes: are
wastes which are
decomposed into harmless
substances by
microorganisms. E. g.
vegetables, fruits, pulses,
cereals, cotton, jute, wool,
wood, leather, paper,
animal dung, animal bones

9. ii) Non biodegradable
wastes :- are wastes which
are not decomposed by
microorganisms. E. g.
polythene bags, plastics,
synthetic fibres, glass,
metals, synthetic rubber,
insecticides, pesticides
etc.

10. Sub-Concept 15.2
Eco-system – What
are its components?

11. Ecosystem : An ecosystem
consists of all the living
organisms in an area along
with the non living
components and their
interaction.
There are different types of
ecosystems. They are :-
i)Natural ecosystems :- like
forests, deserts, grass lands,
mountains, ponds, lakes,

12. ii) Artificial ecosystems :-
like gardens, parks, crop
fields, aquarium, zoo etc.
Components of an
ecosystem:
An ecosystem consists of
two main components. They
are biotic and abiotic
components.

13. i) Biotic components :- are
the living components like
plants, animals
and microorganisms. They
consist of producers,
consumers and decomposers.
Producers :- are green
plants which produce food by
photosynthesis.

14. Consumers :- are
herbivores which get their
food directly from plants,
carnivores which get their
food indirectly from plants
and omnivores which get
their food directly or
indirectly from plants.

15. Decomposers :- are
microorganisms which
decompose dead plants and
animals. They decompose
complex organic substances
into simple inorganic
substances in the soil which
are again used by plants.

16. ii) Abiotic components :- are
the non living components
like air, water, soil,
minerals, sunlight ,
temperature, wind etc.

17. Food chain :
A food chain is the flow of food
energy from one organism to
the next and to the next and so
on. They usually start with a
producer (plants) and end with
a carnivore. In a food chain an
organism gets food from one
group of organisms.

18. Eg: Grass Deer Lion
(producer) (1 consumer) (2 consumer)
Grass Insects Frog Snakes
(producer) (1 consumer) (2 consumer) (3 consumer)
Grass Moth Frog Snake Hawk

21. Food web :
Food web is a group of
several interconnected food
chains. In a food web an
organism gets food from
more than one group of
organisms.

22. 

23. Trophic levels :-
Each step in a food chain
where transfer of food
energy takes place is called
trophic level.
The first trophic level
consists of producers.

24.  The second trophic level
consists of primary
consumers.
 The third trophic level
consists of secondary
consumers.

25. The fourth trophic level
consists of tertiary
consumers.
Since the transfer of food
energy decreases at every
trophic level, the number
of trophic levels are limited
and do not exceed four or
five.

28. Energy flow in trophic
levels
Green plants (producers)
absorb about 1% of solar
energy falling on the
leaves and stores it as
food energy during
photosynthesis.

29. During the transfer of food
energy from one trophic
level to the next, 90% of the
energy is lost to the
environment and only 10%
is transferred to the next
trophic level.

30. So there is a decrease in
the amount of food energy
transferred at every trophic
level by 10%. This is
known as the 10% law.

33. Biological magnification
(Biomagnification)
Harmful chemicals like
insecticides and pesticides
which are used to protect
crops from insects and pests
are absorbed by plants and
enter the food chain. Since
these chemicals are non

34. biodegradable, they get
accumulated at every
trophic level and their
concentration increases.
Since human beings occupy
the highest trophic level,
the concentration of these
harmful chemicals is
maximum in our bodies.

35. The increase in
concentration of harmful
chemicals in the bodies of
organisms at higher
trophic levels is called
biological magnification.

37. Sub-Concept: 15.3
How do our activities
affect the
environment?

38. Depletion of ozone layer in
the atmosphere:
Ozone molecule contains
three oxygen atoms (O3). At
higher levels in the
atmosphere the UV radiation
splits some oxygen
molecules (O2) into free
oxygen atoms which
combines

39. with oxygen molecules (O2)
to form ozone. It is highly
poisonous.
UV radiation
O2 O + O
O2 + O O3

40. The ozone layer present in
the higher layer of the
atmosphere protects the
earth from the harmful UV
radiation from the sun. UV
radiation causes skin cancer
in humans.

41. The ozone layer is being
damaged by the use of
chemicals like chloro fluoro
carbons (CFCs) used in
refrigerators and fire
extinguishers. So the use of
CFCs is now being reduced
to protect the ozone layer.

45. Managing the garbage we
produce :
The household waste is
called garbage. Some of
the garbage is
biodegradable and some
are non biodegradable.
Garbage causes pollution

46. of air, water and soil. So
it should be disposed
properly.
Some of the methods of
garbage disposal are :-
i) Land fills
ii) Recycling
iii) Production of biogas
and manure

47. iv) Preparation
of compost
v) Incineration
vi) Sewage
treatment

48. Sewage treatment
Sewage treatment

49. Summary
The various components
of an ecosystems are
interdependent.
The produces make the
energy from the sunlight
available to rest of the
ecosystem.

50. There is a loss of energy
as we go from one tropic
level to the next this
limits the number of
tropic levels in a food
chain.
Human actvisists have an

51. The use of chemicals like
CFCs has endangered the
ozone layer.
The disposal of waste we
generate is causing
serious environmental
problems.