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1. CHAPTER - 15
OUR ENVIRONMENT
Class :- X
Subject :- Science
Name of Teacher :- Mr. S. K. Ojha (PGT Bio)
School :- KV RRL Jorhat, Assam

2. 1. 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
pollution of air, water and soil.
The waste materials produced are of two main types. They
are biodegradable wastes and non biodegradable wastes.
i) Biodegradable wastes :- are wastes which are
decomposed into harmless substances by microorganisms.
Eg :- vegetables, fruits, pulses, cereals, cotton, jute, wool,
wood, leather, paper, animal dung, animal bones etc.
ii) Non biodegradable wastes :- are wastes which are not
decomposed by microorganisms.
Eg :- polythene bags, plastics, synthetic fibres, glass,
metals, synthetic rubber, insecticides, pesticides etc.

3. 2. Ecosystem and its components :-
a) 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, rivers, oceans etc.
ii) Artificial ecosystems :- like gardens, parks, crop fields, aquarium, zoo etc.
b) Components of an ecosystem :-
An ecosystem consists of two main components. They are biotic and abiotic
components.
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.
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.
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.
ii) Abiotic components :- are the non living components like air, water, soil,
minerals, sunlight , temperature, wind etc.

4. 3a) 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.
eaten by eaten by
Eg:- Grass Deer Lion
(producer) (primary consumer) (secondary consumer)
eaten by eaten by eaten by
Grass Insects Frog Snake
(producer) (primary consumer) (secondary consumer) (tertiary consumer)
eaten by eaten by eaten by eaten by
Grass Moth Frog Snake Hawk
(producer) (primary consumer) (secondary consumer) (tertiary consumer) (quarternary consumer)

6. b) 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.

7. 4) 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.
The second trophic level consists of primary consumers.
The third trophic level consists of secondary consumers.
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.

8. 5) 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.
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. 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.

9. 6) 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 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.
The increase in concentration of harmful chemicals in the bodies of
organisms at higher trophic levels is called biological magnification.

10. 7) Human activities affect the environment :-
a) 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 with oxygen molecules (O2
) to form
ozone. It is highly poisonous.
UV radiation
O2
O + O
O2
+ O O3
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.
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.

12. b) 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 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
iv) Preparation of compost
v) Incineration
vi) Sewage treatment

13. Land fills Recycling
Production of biogas and manure Preparation of compost

14. Incinerator

15. Sewage treatment