Science IX | Natural Resources: Our Environment | Part 3

Natural Resources: Our Environment | Part 3


Soil is the portion of the earth’s surface consisting of disintegrated rock and decaying organic material. It provides the support for many plants and animals. Thickness of soil on the earth’s surface ranges from a few millimeters to 3-4 meters. Terrestrial plants depend for their nutrients, water supply and anchorage upon the soil. Even for the aquatic plants, the soil is important as chief storage of all the nutrients which are made available to the water medium.

1. Formation of soil :

Soil is formed from the rocks by undergoing the following two processes :

1. Weathering ;

2. Paedogenesis

A. Weathering.

Breakdown of bigger rocks into fine smaller mineral particles is called weathering. Weathering occurs by following three means :

(i) Physical weathering :

This is done by various climatic factors such as temperature, wind, rain water, ice, snow, glaciers and running water. Water and high temperature cause corrosive humidity and bring about unequal expansion and contraction or rocks, facilitating their breakdown. Rock pulverizing glaciers, low temperature and water grind the rocks. The freezing water expands in rock crevices and breaks the rocks. Wind action also causes the weathering of rocks. River water grind rock chips and stones into sand and into more fine form – the slit. Soluble components of rocks such as calcium, chloride, sulphates, etc., are removed by water in solution ; they percolate downward. The roots of the plants also have a role in weathering process. They penetrate into the crevices of the rocks and enhance rock-breaking process.

(ii) Chemical weathering :

It involves a variety of chemical processes such as hydrolysis, hydration, oxidation and reduction. Chemical weathering, for example, involves the breaking down of complex compounds by the carbonic acid present in water and by acidic substances derived from the decomposition process of organic matter in soil. The main end products of the chemical weathering are silica, clay, inorganic salts and hydrated oxides.

(iii) Biological weathering :

Lichnes, bryophytes (mosses) and other plants live on rocks and produce acids, which accelerate the process of rock weathering.

B. Paedogenesis (soil development) :

This process involves the decomposition process by bacteria and fungi by which organic material s are broken down and leads to humification and mineralization. Detritivores such as nematodes, earthworms and artropods such as scolopendra, millipede, mites and ants consume organic matter and add excretory nitrogen to it. Thus, addition of organic matter (humus) from dead and decomposed plants and animals is the final stage in the formation of soil. A mature soil has minerals, stored energy in the form of organic matter (such as starch, sugars, cellulose, lipids, proteins, oxides of nitrogen (NO2, NO3, NH+ ions), water and air.

Soil Erosion

The removal and transportation of top layer of soil from the original position to another place with the help of certain agents such as strong winds and fast running rainwater is called soil erosion. The top layer of soil is fertile. It provides anchorage (firm support) to plants and is also source of nutrients and water to the plants.

Soil erosion normally occurs n bare areas, i.e., areas without plant cover. It is so because the bare topsoil is loose and thus can easily carried away by strong winds or fast moving water of heavy rains or rivers.

Biogeochemical Cycles

A constant interaction between the biotic and abiotic components of the biosphere makes it a dynamic, but stable system. These interactions consist of a transfer of matter and energy between the different components of the biosphere. Let us look at some processes involved in the maintenance of the above balance.

The Water or Hydrological cycle

Water evaporates from the hydrosphere (oceans, seas, rivers, streams, lakes, ponds, moist soil) with sun’s heat and forms clouds. By the help of wind, the clouds are blown over the land, where they are cooled enough to drop the water as rain, hail and sleet (called precipitation). Rain may fall directly into the oceans also.

The organisms get water from and return it to the global water cycle. Plants absorb water from the soil or water reservoir and ad it to the air as vapour by transpiration. Water transpired by trees cools the surrounding air, and plays a role in determining the microclimate around them. Animals take water from the water reservoir or with food (plants, or other animals or their products). They return it to the air as vapours by respiration or to the soil as fluid by excretion. Mammal excrete water also as sweat which evaporates from their bodies. Water is also added to the environment by death and decay of organisms. Water vapor formed by transpiration and respiration form clouds and enter global water cycle.

The Nitrogen Cycle

In our atmosphere nitrogen gas makes up 78% nitrogen one of the essential part of living molecule like protein, nucleic Acid (DNA & RNA) and vitamins. It also found in alkalides and urea which are important biologically compounds.

Nitrogen is thus in essential nutrient for all life form and life would be simple if all these life forms could use the atmospheric nitrogen directly. However, other than a few form of bacteria, life form are not able to convert the comparatively inert nitrogen molecule into form like nitrates and ‘nitrites fixing’ bacteria are found in roots of legumes plants (Generally the plants which give us pulses). The other manner in which the nitrogen molecules are converted into nitrates and nitrites by physical process. During lighting the high temperature and pressure created in the air convert nitrogen into oxides of nitrogen. These oxides dissolves in water to form nitric and nitrous acid and fall an land along with rain. These re them utilized by various life forms.

Plants generally take up nitrates and nitrites and convert them into Amino Acid which are used to make proteins and other complex biological compound are subsequently consumed bacteria Animals. Once the animals or the plant dies, other bacteria in the soil convert the various compound of nitrogen back into nitrates and nitrites. A different type of bacteria converts the nitrates and nitrites into elemental nitrogen. In this way nitrogen cycle occur in our atmosphere.

The Carbon Cycle

Carbon is found in various forms on the Earth. It occurs in the elemental form as diamonds and graphite. In the combined state, it is found as carbon dioxide in the atmosphere, as carbonate and hydrogen carbonate salts in various minerals, while all life forms are based on carbon containing molecules like proteins, carbohydrates, fats, nucleic acids and vitamins. The endoskeletons and exoskeletons of various animals are also formed from carbonate salts. Carbon is incorporated into life forms through the basic process of photosynthesis which is performed in the presence of sunlight by all life forms that contain chlorophyll. This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules. These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other biologically important molecules.

The utilization of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide. This carbon dioxide then goes back into the atmosphere. Another process that adds to the carbon dioxide in the atmosphere is the process of combustion where fuels are burnt to provided energy for various needs like heating, cooking, transportation and industrial processes. In fact, the percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossils fuels on a very large scale. Carbon, like water, is thus cycled repeatedly through different forms by the various physical and biological activities.

The Oxygen Cycle

Oxygen is a very abundant element on our Earth. It is found in the element form in the atmosphere to the extent of 21%. It also occurs extensively in the combined form in the Earth’s crust as well as also in the air in the form of carbon dioxide. In the crust, it is found as the oxides of most metals and silicon, and also as carbonate, sulphate, nitrate and other minerals. It is also an essential component of most biological molecules like carbohydrates, proteins, nucleic acids and fats (or lipids).

But when we talk of the oxygen-cycle, we are mainly referring to the cycle that maintains the levels of oxygen in the atmosphere. Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. And this forms the broad outline of the oxygen-cycle in nature.

Though we usually thing of oxygen as being necessary to life n the process of respiration, it might be interest to you learn that some forms of life, especially bacteria, are poisoned by elemental oxygen. In fact, even the process of nitrogen-fixing by bacteria does not take place in the presence of oxygen.


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.