NCERT Book Class 12 Biology Environmental Issues

ENVIRONMENTAL ISSUES

Introduction

Human population size has grown enormously over the last hundred years. This means increase in demand for food, water, home, electricity, roads, automobiles and numerous other commodities. These demands are exerting  tremendous pressure on our natural resources, and arealso contributing to pollution of air, water and soil. The need of the hour is to check the degradation and depletion of our precious natural resources and pollution without halting the process of development. Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil. Agents that bring about such an undesirable change are called as pollutants. In order to control environmental pollution, the Government of India has passed the Environment (Protection) Act, 1986 to protect and improve the quality of our environment (air, water and soil).

16.1 AIR POLLUTION AND ITS CONTROL

We are dependent on air for our respiratory needs. Air pollutants cause injury to all living organisms. They reduce growth and yield of crops and cause premature death of plants. Air pollutants also deleteriously affect the respiratory system of humans and of animals. Harmful effects depend on the concentration of pollutants, duration of exposure and the organism. Smokestacks of thermal power plants, smelters and other industries release particulate and gaseous air pollutants together with harmless gases, such as nitrogen, oxygen, etc.

These pollutants must be separated/ filtered out before releasing the harmless gases into the atmosphere. There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator (Figure 16.1), which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant. It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.

These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the  dust to fall. A scrubber (Figure 16.1) can remove gases like sulphurdioxide. In a scrubber, the exhaust is passed through a spray of water or lime. Recently we have realised the dangers of particulate matter that are very very small and are not removed by these precipitators. According toCentral Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health. These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature deaths.

EXERCISES

1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.

2. List all the wastes that you generate, at home, school or during your trips to other places, could you very easily reduce? Which would be difficult or rather impossible to reduce?

3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?

4. Match the items given in column A and B: Column A Column B

 (a) Catalytic converter (i) Particulate matter

 (b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides

 (c) Earmuffs (iii) High noise level

 (d) Landfills (iv) Solid wastes

5. Write critical notes on the following:

 (a) Eutrophication

 (b) Biological magnification

 (c)Groundwater depletion and ways for its replenishment

6. Why ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?

7. Discuss the role of women and communities in protection and conservation of forests.

8. What measures, as an individual, you would take to reduce environmental pollution?

9. Discuss briefly the following:

 (a) Radioactive wastes

 (b) Defunct ships and e-wastes

 (c) Municipal solid wastes

10. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?

11. Discuss briefly the following :

 (a) Greenhouse gases

Please refer to attached file for NCERT Class 12 Biology Environmental Issues