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NCERT Solutions for Class 9th Science

 

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Chapter 14. Natural Resources

Chapter Review

 

 

 

Chapter-Review

 

  • Life on Earth depends on resources like soil, water and air, and energy from the Sun.
  • We need to conserve our natural resources and use them in a
    sustainable manner.
  • Water covers 75% of the Earth’s surface.
  • The air that covers the whole of the Earth like a blanket, is called
    the atmosphere.
  • This life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible, is known as the biosphere.
  • Living things constitute the biotic component of the biosphere.
  • The air, the water and the soil form the non-living or abiotic component of the biosphere.
  • Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour.
  • Carbon dioxide constitutes up to 95-97% of the atmosphere on Venus and Mars.
  • Eukaryotic cells and many prokaryotic cells need oxygen to break down glucose molecules and get energy for their activities.
  • The process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion.
  • Carbon dioxide is ‘fixed’ in two ways: (i) Green plants convert carbon
    dioxide into glucose in the presence of Sunlight and (ii) many marine animals use carbonates dissolved in sea-water to make their shells.
  • Air is a bad conductor of heat.
  • The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year.
  • During the night, atmosphere slows down the escape of heat into
    outer space.
  • The surface of moon has the temperature ranges from -119 C to 110 C due to no atmosphere. 
  • Uneven heating of air over land and water-bodies causes winds.
  • Evaporation of water from water-bodies and subsequent condensation give us rain.
  • Water vapour is formed due to the heating of water bodies and the activities of living organisms.
  • The atmosphere can be heated from below by the radiation that is
    reflected back or re-radiated by the land or water bodies. On being heated, convection currents are set up in the air.
  • Rainfall patterns are decided by the prevailing wind patterns.
  • The hot air rises up carrying the water vapour with it.
  • The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur.
  • On burning fossil fuels produces different oxides of nitrogen and sulpher. 
  • Oxides of sulpher and nitrogen dissolve in rain to give rise to acid rain.
  • The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.
  • Presence of hight levels of pollutants in fog cause visibility to be lowered, this is known as smog. This indicates air pollution. 
  • An increase in the content of harmful substances in air is called air
    pollution
    .
  • Water occupies a very large area of the Earth’s surface and is also found underground.
  • Most of the water on Earth’s surface is found in seas and oceans
    and is saline.
  • Fresh water is found frozen in the ice-caps at the two poles and on snowcovered mountains. The underground water and the water in rivers, lakes and ponds is also fresh.
  • All cellular processes take place in a water medium.
  • 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 the body to the other in a dissolved form.
  • organisms need to maintain the level of water within their bodies in order to stay alive.
  • Terrestrial life-forms require fresh water for  because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water.
  • The quality of the topsoil is an important factor that decides
    biodiversity in that area.
  • The sun, water, wind and some living organism like Lichen help in formation of soil.
  • Removal of surfaces of soil by water and wind is known as soil erosion.  
  • The upper most layer of earth contains bits of decayed living organisms which is called humus.
  •  Humus is a major factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.
  • The mineral nutrients that are found in a particular soil depends on the
    rocks it was formed from.
  • The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil.
  • The quality of the topsoil is an important factor that decides biodiversity in that area.
  • Use of large amounts of fertilizers and pesticides over long periods of time can destroy the soil structure by killing the soil micro-organisms that recycle nutrients in the soil.
  • The roots of plants have an important role in preventing soil erosion.
  • The water-cycle, the nitrogen-cycle, the carbon-cycle, the oxygen-cycle are parts of biogeochemical cycles. 
  • Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins.
  • Nitrogen-fixing bacteria fixes atmospheric nitrogen to ntrates and nitrites. 
  • Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins.
  • 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.
  • The process of photosynthesis converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.

 

 

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