14. Natural Resources Class 9 science Solutions English Medium-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 -119^० C to 110^० 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.