Science IX | Natural Resources: Our Environment | Part 2

Natural Resources: Our Environment | Part 2


As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. Such process of condensation of water is facilitated when dust and other suspended particles act as the ‘nucleus’ for these droplets to form around. An enormous collection of tiny droplets of water appear in the form of clouds. These droplets of water, once formed, slowly grow bigger by condensation of more water droplets. When the droplets have grown big and heavy, they fall down in the form of rain. Occasionally, when the temperature of air is very low, precipitation then may occur in the form of snow, sheet or hail.

Pattern of Rainfall in India

India receives most of the rain from the monsoon winds only. In summer season south-west monsoon is active while during winter season north-east monsoon is active. The south-west monsoon blows in from sea to land. The hot air that rises over South Asia during April and May creates low pressure areas into which the cooler, moisture bearing winds from the Indian Ocean flows. These air circumstances set off a rush of moisture rich air from the Southern seas over South Asia.

Air Pollution

The present day industrial growth has polluted air to a greater extent by releasing SO2, CO2, CO, oxides of nitrogen, H2S< fumes of acids, dust particles of unburnt carbon, lead, asbestos and even cement. For example, the burning of coal and oil to generate electric power, run factories and fuel automobile engines creates oxides of nitrogen and sulphur that acidify the rain.

Air Pollution

Air carries many undesirable substances or impurities which are not good for our health. The chief constituents of the impurities of air include (i) carbon dioxide, (ii) carbon monoxide, (iii) oxides of sulphur; (iv) oxides of nitrogen; (v) fluoride compounds; (vi) metals (e.g., lead, nickel, arsenic, cadmium, tin, etc); (vii) hydrocarbons (e.g., benzene), (viii) particulate matter (dust, grit, fly ash) and (ix) toxicants. All these impurities are called pollutants. They cause air pollution.

These air pollutants can cause respiratory problems, renal problems, high blood, pressure, problems in nervous system, eye irritation, etc., in the human beings. Many injurious effects such as falling of leaves, reduced growth, degeneration of chlorophyll, mottling of leaves, etc., have been reported in plants. Lichens are found to be very sensitive to the levels of contaminants such as sulphur dioxide present in polluted air.

Normally, you will observe lichens on the barks of trees as greenish-white crust. On the trees near busy roads, the incidence of lichens would be less as also observe more incidence of lichens on the barks of trees on the sides away from the roads as compared to the sides towards the roads. It is so because on by burning of the fossil fuels (diesel, petrol). Increased levels of air pollutants such as sulphur dioxide in the air around the busy roads reduce the incidence of lichens on the trees near roads as the are sensitive to increased level of air pollutants such as sulphur dioxide.

Air pollution also results in two serious in two serious ecological problems of global magnitude green house effect and peeling of ozone umbrella.

The carbon dioxide of the atmosphere keeps the earth warm, much like the glass which keeps the greenhouse warm. This effect is called the greenhouse effect. The increase in carbon dioxide in the atmosphere has intensified the greenhouse effect and has led to global warming, i.e., an increase in the average temperature of the earth.

Ozone layer also protects oxygen existing at lower altitudes from ill effects of UV rays. Recently, reduction in ozone levels over the Antarctic has been known as hole in ozone layer (fig.). This has posed the threat of damages to inhabitants of earth from shortwave UV rays.


About three fourth of the earth’s surface (i.e., 75 percent) is covered with hydrosphere, the main component of which is water. Major part of water is found in seas and oceans. Most of the water of our utilization on the earth comes from rivers, lakes, ponds and even underground wells. Fresh water forms only about 2.5 per cent of water and major part of this fresh water is frozen in glacial ice. So a very small amount (about 0.5 percent) remain there for the living being to perform all living activities.

Water is one of the most unusual natural compound found on earth and it is also one of the most important. The water remains in solid (snow), liquid (water) and gaseous (water vapour) forms. Life on earth began in seas and water in some form or the other is absolutely essential for the maintenance of all life. Water is one of the agent in soil formation and serves as living medium for several different ecosystems. We too use water for drinking, washing of utensils and clothes, sewage disposal, irrigation and in various industries.

All the reactions that take place within our body and within the cells occur between substances that are dissolved in water. Substances are also transported from one part of body to the other in dissolved form. Hence, the organisms need to maintain a distinct level of water within their bodies in order to stay alive. Terrestrial – life forms require fresh water for this purpose because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water. Thus, water sources need to be easily accessible for animals and plants to survive on land.

Water pollution

An undesirable change in the physical, biological or chemical qualities of water (due to addition of foreign organic, inorganic, biological or radioactive substances) that adversely affects the aquatic life and makes water unfit for use, is called water pollution. In other words water pollution is contamination of fresh water (or sea water) due to addition of harmful substances making it unfit for use by the biota. Pollution of water is one of most serious environmental problems of world.

Water pollution may be of following three types :

1. Surface water pollution (or Inland water pollution).

2. Underground water pollution

3. Marine water pollution. Human being is the main cause of water pollution. However, some pollution also occurs naturally. Soil particle enter water by soil erosion; minerals dissolve in water from rocks and soil; animal wastes and dead fallen leaves (litter) and into water sources.


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