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1. Effect of adding waste to the environment :-:

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.

2. Ecosystem and its components :-:

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 .

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i ) 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 .

3a) Food chain :-:

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)

b) Food web :-:

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 .

4) Trophic levels :-:

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.

5) Energy flow in trophic levels :-:

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.

6) Biological magnification (Biomagnification) :-:

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.

7) Human activities affect the environment :- :

7) Human activities affect the environment :- a) Depletion of ozone layer in the atmosphere :- Ozone molecule contains three oxygen atoms (O 3 ). At higher levels in the atmosphere the UV radiation splits some oxygen molecules (O 2 ) into free oxygen atoms which combines with oxygen molecules (O 2 ) to form ozone. It is highly poisonous. UV radiation O 2 O + O O 2 + O O 3 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.

b) Managing the garbage we produce :-:

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

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Land fills Recycling Production of biogas and manure Preparation of compost

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Sewage treatment

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