Thursday, November 18, 2021

15. Our Environment | Class 10 CBSE | Web Notes | Part 2: How do our Activities Affect the Environment?



Ozone Layer and its Depletion

-   Ozone (O3) is a deadly poison. However, at the higher levels of the atmosphere, ozone shields the earth surface from dangerous ultraviolet (UV) radiation from the Sun. UV radiation causes harmful effects such as skin cancer.

-   At the higher levels of the atmosphere, the higher energy UV radiations split some O2 into free oxygen (O) atoms. They combine with O2 to form ozone (O3).

O2  O + O

O + O2 → O3

-   In 1980s, the amount of ozone began to drop sharply. It was due to chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers.

-   In 1987, the United Nations Environment Programme (UNEP) made an agreement to freeze CFC production at 1986 level. It is now mandatory to make CFC-free refrigerators.

-   Other ozone depleting substances: Hydrofluorocarbons (HFCs), halons etc.

-   The size of the ozone hole has reduced in recent years.

Managing the Garbage we Produce

-   Garbage are the unwanted materials that people have thrown away.

-   In organisms, specific enzymes are needed to break-down a particular substance. So, if we eat coal, we do not get energy. Similarly, bacteria or other saprophytes have no enzymes to break down artificial materials like plastics.

-   Substances that are broken down by biological processes are called biodegradable. E.g. Fruits, vegetables, leaves, meat, paper, rubber etc.

-   Substances that are not broken down by biological processes are called non-biodegradable. They are inert and persist for a long time or may harm the ecosystem. E.g. Plastics, glass, nylon etc.

Non-biodegradable substances

Average time to break down

Glass bottle

500 years

Plastic bags

10-20 years

Plastic container

50-80 years

Plastic soda bottle

450 years

Nylon fabric

30-40 years

-   There are biodegradable plastics such as Polylactic acid, Polyhydroxyalkanoates, Polybutylene succinate etc.

-   At home and class room, there are various biodegradable and non-biodegradable wastes produced. They have to be collected separately and treated properly.

-   The local body (panchayat, municipal corporation, resident welfare association) have mechanisms to treat biodegradable & nonbiodegradable wastes separately.

-   Improvements in life-style and changes in attitude have generated much amount of waste material.

-   Changes in packaging have resulted in much of our waste becoming nonbiodegradable.

Disposable cups in trains

-   Disposable plastic cups are non-biodegradable. An alternative was kulhads, (disposable clay cups). But making these result in the loss of the fertile top-soil. Now disposable paper-cups are used. It is better than plastic cups because it is biodegradable and do not affect the property of drinks in the cup.

Electronic & electrical wastes (e-wastes) include mobile phones, computers, televisions etc. They contain dangerous chemicals such as mercury, lead, cadmium, polybrominated flame retardants, barium and lithium. They cause damage to brain, heart, liver, kidney and skeletal system.  

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