Class 9th Science: Chapter 14 Natural Resources
Materials provided by nature on earth which can be used by living organisms are termed to be natural resources. Three different regions of earth are lithosphere, hydrosphere and atmosphere.
• The solid outermost layer of the earth’s crust and the rigid upper part of its mantle is called the lithosphere.
• The water that is found on the earth’s surface, above it as clouds and below it as groundwater, is called the hydrosphere.
• The air which includes gases that cover the earth like a blanket, is called the atmosphere.
The region on earth comprising of both biotic and abiotic components is called as biosphere.
• Biotic components include all the living organisms.
• Abiotic components include air, water and the soil.
Biotic components interact with all the abiotic components such as air, water and soil to sustain their life.
Air is a mixture of gases like nitrogen, oxygen, carbon dioxide and water vapour.
• Nitrogen is used to produce a number of organic molecules like proteins. Nitrogen is fixed in plants and is transferred to animals through food chain.
• Oxygen is used by plants and animals in the process of respiration. The combustion of fossil fuels also requires oxygen.
• Carbon dioxide is used by plants in the process of photosynthesis. Marine animals absorb atmospheric carbon dioxide to form carbonic acid. These carbonate ions are used by marine animals to make shells.
Functions of Air:
• It helps to maintain a steady temperature on Earth during the day
• It controls the climate.
• It helps in the formation of rain.
• The atmosphere on earth prevents the increase of temperature during day time. Atmosphere slows down the heat from escaping to outer space during night time.
Sea breeze and land breeze:
During the day, air moving from the high pressure area over the sea to the low pressure area over land creates sea breeze. During night, since soil cools faster than water, the air above the land is cooler than the air above the sea. Now, the air moving from the high pressure area over land to the low pressure area over the sea creates land breeze.
Formation of rain:
Water bodies get heated during the day and evaporate into the air. As the vapour rises, it cools. This causes the vapour to condense into tiny water droplets, which fall down as rain by the process of precipitation.
Air moving from an area of high pressure to an area of low pressure causes winds. Rains are brought by seasonal winds called as monsoons. Based on rainfall pattern, regions of India can be classified into three types, namely heavy rainfall regions, moderate rainfall regions and low rainfall regions. Regions receiving heavy rainfall exhibit high biodiversity.
The contamination of air with chemicals, smoke, dust particles and disease-causing agents is called air pollution.
Water is essential for the survival of plants and animals, as cellular processes take place in a water medium. Water is found on the Earth’s surface, under the ground and in the atmosphere as water vapour. Maximum amount of water available is marine water which is salty. Most of the fresh water available on the earth is in the form of frozen ice.
The contamination of water by sewage, chemicals, detergents, fertilisers and other harmful substances is called water pollution. Increase in water temperature due to pollutants decreases the amount of dissolved oxygen. Dissolved oxygen is the source of oxygen for aquatic organisms. Reduction of dissolved oxygen results in the death of many aquatic organisms.
Soil is another important natural resource that supports life. Soil contains soil particles, humus and living organisms. It also contains some amount of water in the form of droplets or air in between the soil particles.
Formation of soil:
Soil is formed by many factors like sun, water, wind and living organisms.
• Uneven contraction and expansion of rocks, cracks and breaks them into smaller particles of soil.
• Frozen water logged in the cracks of rocks, cracks and breaks the rocks into soil.
• Lichens growing on the surface of rocks release chemicals which powder the rocks into soil.
• Flowing water in rivers breaks hard rocks into soil particles.
• Strong winds erode rocks and carry sand particles.
The addition of substances that adversely affect soil fertility is called soil pollution. Use of fertilisers killed lot of useful microorganisms and reduced soil fertility. Deforestation has lead to erosion of topmost fertile layer of the soil. Overgrazing by animals also led to the soil erosion. Fine particles of water are also carried away by wind and water.
The cycling of chemicals between the biological and the geological world is called biogeochemical cycle.
The biotic and abiotic components of the biosphere constantly interact through biogeochemical cycles. During these interactions, there is a transfer of nutrients between living organisms and the non-living environment.
The four important biogeochemical cycles are water cycle, nitrogen cycle, carbon cycle and oxygen cycle.
The water cycle involves various steps like evaporation, transpiration, condensation and precipitation.
• When the water bodies are heated during the day, water enters the atmosphere as water vapour by the process of evaporation.
• There is another way in which water evaporates into the atmosphere. This happens through transpiration.
• The water vapours in the atmosphere changes to water droplets and collects to form clouds. This process is called condensation.
• Air currents move the clouds formed by condensation and carry them over the land, where they break into rain, snow or fog. This is called precipitation.
The sequence in which nitrogen passes from the atmosphere to the soil and organisms, and then is eventually released back into the atmosphere, is called the nitrogen cycle.
• Nitrogen makes up 78 percent of the earth’s atmosphere. The percentage of nitrogen in the atmosphere is maintained by nitrogen cycle.
• Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins, and chlorophyll.
• Plants and animals cannot utilise atmospheric nitrogen readily. It has to be fixed by some organisms called as nitrogen fixers.
• Nitrogen-fixing bacteria like Rhizobium live in symbiotic association in the root nodules of certain leguminous plants.. These bacteria convert atmospheric nitrogen into ammonia, which is utilised readily by plants.
• Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90 percent of nitrogen fixation.
• Lightning plays an important role in nitrogen fixation. When lightning occurs, the high temperature and pressure convert nitrogen and water into nitrates and nitrites.
• Nitrates and nitrites dissolve in water and are readily used by aquatic plants and animals.
• Ammonification is the process by which soil bacteria decompose dead organic matter and release ammonia into the soil.
• Nitrification is the process by which ammonia is converted into nitrites and nitrates.
• Denitrification is the process by which nitrates are converted into atmospheric nitrogen.
Carbon is cycled repeatedly through different forms by the various physical and biological activities constituting the carbon cycle.
• The carbon cycle starts in plants. Plants use carbon dioxide in the atmosphere to synthesise glucose in the presence of sunlight by the process of photosynthesis. Glucose is a form of carbohydrates.
• Plants and animals break these carbohydrates to produce energy and release carbon dioxide through respiration.
• Plants and animals, after they die, are decomposed by decomposers to release carbon in the form of carbon dioxide.
• Some dead plant and animal remains, in the soil, are converted into coal, petroleum and natural gas, better known as fossil fuels. Burning of fossil fuels releases carbon dioxide into atmosphere. Fossil fuels are used for cooking, transportation and in the industries. The balance between the biological and geological world is maintained.
The sequence in which oxygen from the atmosphere is used by organisms and eventually released back into the atmosphere through photosynthesis is called as oxygen cycle.
• Oxygen makes up 21 percent of the air. It is an essential constituent of carbohydrates, proteins, fats and nucleic acids.
• Oxygen is found in air, in combined form as carbon dioxide, and in the earth’s crust as carbonates, sulphates and nitrates.
• Plants and animals use atmospheric oxygen during respiration and release the same during photosynthesis.
• Fossil fuels require oxygen for combustion.
• The ozone layer is present in stratosphere, one of the layers of the atmosphere. Each molecule of ozone is made up of three oxygen atoms. The ozone layer prevents harmful radiations from reaching the earth’s surface, where they might damage life forms.
Solar radiation reaching the earth is reflected back into the atmosphere. Much of the heat is lost to the environment. But some of the energy is trapped by the atmosphere thereby causing Greenhouse effect.
<< Back to NCERT Solutions of Class 9th Science
<< Back to NCERT/CBSE Notes