CBSE Class 9 Science Notes - Natural resources 

 These resources, essential for human life and the functioning of ecosystems, are called natural resources because they are sourced directly from nature. Life on Earth thrives due to its favorable conditions, including ambient temperature, access to water, and food availability. The planet provides these necessities through various resources like land (the lithosphere), water (the hydrosphere), and air (the atmosphere). These resources, combined with energy from the sun, sustain the biosphere, the life-sustaining zone where the lithosphere, hydrosphere, and atmosphere interact. 

1.0Natural Resources Classification

The Breath of Life : Air

• Air is a mixture of many gasses like nitrogen, oxygen, carbon dioxide, water vapor and some others present in the atmosphere. Air is an important inexhaustible natural resource.

• Earth's atmosphere has a series of layers. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Importance of atmosphere

• Role of atmosphere in climate control : The atmosphere acts as a protective blanket for the Earth. Since the atmosphere is a bad conductor of heat, it keeps the average temperature of the Earth fairly constant during the day and even during the course of the whole year. The atmosphere prevents the sudden increase in temperature during daylight hours. And during the night, it slows down the escape of heat into outer space. Thus, the Earth receives just the right amount of heat, which helps in climate control and allows living organisms to exist. 
• The movement of air-winds : The atmosphere gets heated from the radiation that is reflected back or re-radiated by the land or water bodies. As a result of heating, convection currents are set up in the air. Since land gets heated faster than water, the air over land gets heated faster than the air above water bodies. 
• In coastal regions, during the day, the air above the land gets heated faster and starts rising. So a region of low pressure is created and air over sea moves into this area of low pressure. 
• The movement of air from one region to the other region causes winds. During the day, the direction of wind would be from the sea to the land and at night, both land and sea starts to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land, thus the direction of wind would be from the land to the sea. 

Rain 

• When water bodies are heated during the day, a large amount of water evaporates and goes into the air. 
• The wind carries the water vapor to various places. The air gets heated and rises up carrying the water vapor with it. 
• As this air rises, it expands and cools causing the water vapor in the air to condense in the form of tiny droplets. 
• Once the water droplets are formed, they grow bigger by the 'condensation' on these water droplets. When the drops grow big and heavy, they fall down in the form of rain. Rainfall patterns are decided by the wind patterns. 

Air pollution 

• Air pollution affects the respiratory system causing breathing difficulties and diseases such as bronchitis, asthma, lung cancer, tuberculosis and pneumonia.
• Burning of fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur inhalation of these gasses is dangerous. These gasses also dissolve in rain to give rise to acid rain.
• The combustion of fossil fuel also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons. The presence of high levels of all these pollutants, reduce visibility in cold weather where water also condenses out of air forming smog. Smog is an indication of air pollution. 
• Regular breathing in the polluted air increases the incidence of allergies, cancer and heart diseases. 
• Acid Rain : It is the rain which contains a small amount of acid in it that is formed from the gasses like sulphur dioxide and nitrogen oxides present in polluted air. It causes damage to the living and nonliving things. 

2.0Water—a wonder liquid

• All cellular processes take place in water medium.  
• All 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 the body to the other in a dissolved form. 
• Organisms need to maintain the level of water within their bodies in order to survive. 
• Terrestrial life forms require fresh water because their bodies cannot tolerate or can not get rid of the high amount of dissolved salts in saline water.  
• The availability of water is the major resource which determines the diversity of life on land. 

Water pollution 

Ways by which water is polluted:

• Agricultural substances such as fertilizers and pesticides are used to increase crop yield, and some percentage of these is washed into the water bodies that pollute the water. 
• Sewage from homes and waste from factories are dumped into rivers or lakes. 
• Hot and cold water discharged from industries make a change in temperature, which is harmful for aquatic organisms. 
• All these affect the balance among various organisms that are found in water bodies. 

Water pollution refers to: 

• Addition of undesirable substances to water bodies: The substances like fertilizers and pesticides used in farming, mercury salts used by paper industries could be poisonous. There could also be disease-causing organisms, like the bacteria which causes-cholera. 
• Removal of desirable substances from water bodies : Industrial or household waste reduces the dissolved oxygen in water bodies, thereby affecting aquatic life. 
• A change in temperature: Aquatic organisms can stay alive in a certain range of temperature. Sudden change in temperature of water bodies is dangerous for aquatic organisms and affects their breeding.

3.0Soil 

• It forms the upper surface of the land and supports plant growth. 
• Soil is the layer of unconsolidated particles derived from weathered rock, organic matter (humus), water and air. 
• Soil is an important resource that decides the diversity of life in an area. 
• The outermost layer of our Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life forms. 

Factors or Processes for soil formation:

• The Sun : The Sun heats up rocks during the day so that they expand. At night, the rocks cool down and contract. The unequal expansion and contraction in different parts of the rock results in the formation of cracks and ultimately rocks break up into smaller pieces. 
• Water : Water helps in the formation of soil in two ways : Firstly, water could get into the cracks in the rocks formed due to uneven heating by the Sun. If this water freezes, it will widen the cracks. Secondly, fast flowing water carries big and small particles of rock downstream, causing breakdown of rock particles into smaller, finer particles through their abrasive effects. 
• Wind: Strong winds also erode rocks down. They also carry sand from one place to the other like the water does. 
• Living organisms also influence the formation of soil : While lichens grow on the surface of rocks, they release certain substances that cause the rock surface to powder down and form a thin layer of soil. Small plants like moss and roots of big trees also break the rocks. 

Components of soil:

• It contains small particles of rocks that vary in size (sand > silt > clay).  
• It contains bits of decayed living organisms which are called humus.  
• Soil also contains various forms of microscopic life. 
• It contains nutrients and availability of which depends on the rocks from which it was formed.  
• It contains air & water.

Soil Pollution

• It is the removal of useful components from the soil and addition of other substances, which adversely affect the fertility of the soil and kill the diversity of organisms that live in it. 
• Use of large amounts of fertilizers and pesticides destroy the soil structure by killing soil microorganisms that recycle nutrients in the soil. 
• It also kills the earthworms which are instrumental in making the rich humus thus affect the fertility of soil.

Soil Erosion 

It is the removal and thinning of the fertile top soil from a region due to climatic and physical processes, such as high rainfall and wind etc. Soil erosion occurs easily where the soil is not covered by vegetation.

Causes of soil erosion:

• Wind causes soil erosion by carrying away the top soil particles. 
• Rain causes soil erosion on unprotected topsoil by washing it down. 
• Improper farming or tilling and leaving the field fallow for a long time causes soil erosion. 
• Frequent flooding of rivers causes soil erosion by removing the topsoil of the fields near the river banks. 
• Deforestation also leads to soil erosion.

Prevention of soil erosion:

• It can be prevented by intensive cropping.
• It can be prevented by providing proper drainage canals around the fields. 
• Soil erosion in hilly areas can be prevented by practicing terrace farming. 
• It can be prevented by planting trees and sowing grasses. 
• It can be prevented by constructing strong embankments along the river banks. 

4.0Biogeochemical Cycles 

• The cyclic flow of nutrients between non-living environments and living organisms is known as biogeochemical cycles. 
• It is the process of transfer and circulation of the essential chemical nutrients such as Carbon, Hydrogen, Oxygen and Nitrogen in a biosphere.

1. Water Cycle

• The water cycle is the continuous movement of water on Earth through various processes. It starts with evaporation, where water from oceans, lakes, and rivers turns into water vapor due to the sun's heat. Plants release water through  transpiration. 
• The vapor rises, cools, and undergoes condensation to form clouds. 
• When clouds become heavy, precipitation occurs in the form of rain, snow, or hail. 
• The water either infiltrates into the ground, replenishing groundwater, or flows as runoff back into bodies of water, completing the cycle. 
• This process is vital for maintaining water availability and supporting life.

2. Nitrogen Cycle

• The source of nitrogen is the atmosphere which contains 78 percent of nitrogen in the form of gas. Nitrogen is thus an essential nutrient for all life forms. 
• Nitrogen-cycle in the biosphere involves the following important steps.  
• Nitrogen fixation : The process is converting atmospheric nitrogen into usable form (nitrates, ammonium ions) which are soluble in water. This is done by various N2 fixing bacteria e.g., Rhizobium, blue green algae and bacteria azotobacter. Other than these bacteria, the only other manner in which the nitrogen molecule is converted to nitrates and nitrites is by a physical process. During lightning, the high temperature and pressure created in the air convert nitrogen into oxides of nitrogen which dissolve in water to give nitric and nitrous acids and fall on land along with rain which is then utilized. 
• Ammonification: It is the process of decomposing complex, dead organic matter into ammonia. This is done by microorganisms living in the soil e.g., bacteria and fungi. 
• Nitrification : It is the process of conversion of ammonia into nitrites and then into nitrates. This is done by nitrifying bacteria e.g., Nitrosomonas and Nitrobacter. 
• Denitrification : It is the process of reducing nitrates present in the soil to release nitrogen gas back into the atmosphere e.g., Pseudomonas. Thus, there is a nitrogen cycle in nature in which nitrogen passes from its elemental form in the atmosphere into simple molecules in the soil and water, which gets converted into more complex molecules in living beings and back again to the simple nitrogen molecule in the atmosphere

3. The Carbon Cycle 

• Carbon is found in various forms on the Earth. It occurs in the elemental form as diamond and graphite. In abiotic environment, carbon is present in the following forms: 
• As carbon dioxide in the atmosphere. 
• As carbonate and hydrogen-carbonate salts in various minerals. 
• As dissolved carbonic acid and bicarbonates in water.
• As fossil fuels like coal, petroleum and natural gas. Plants utilize the atmospheric carbon dioxide in photosynthesis to produce carbohydrates, which are taken by herbivores and then pass through small and large carnivores. Many marine animals use carbonates dissolved in seawater to make their shells. 

4. The Oxygen Cycle

• Oxygen constitutes about 21 percent of the atmospheric gasses. 
• It is also present in dissolved form in water bodies and helps in the survival of aquatic life. 
• Oxygen is also present in combined forms such as carbon dioxide (CO2 ) and water (H2O). 
• In the earth's crust oxygen 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.  
• Oxygen cycle maintains the level 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. 
• All living organisms, plants, animals and decomposers take oxygen from their surroundings and utilize it for respiration. 
• Oxygen is returned to the atmosphere in only one major process, i.e., photosynthesis. Green plants are a major source of oxygen in the atmosphere.