Important Questions for CBSE Class 9 Science Chapter 14 – Natural Resources

Important Questions Class 9 Science Chapter 14 – Natural Resources

Science is a complex subject as it involves various branches like Physics, Chemistry, Biology, Geology etc. Therefore, it is considered to be one of the utmost essential subjects in the academic curriculum; hence, students must study it sincerely.

The chapter ‘Natural resources’ studies all the natural resources available on earth by nature and how one should use them carefully to keep our planet eco-friendly. The vital topics included in Chapter 14 Class 9 Science important questions are

  • Natural Resources
  • The Breath of Life: Air
  • Water: A Wonder Liquid
  • Mineral Riches in the Soil
  • Biogeochemical Cycles
  • Ozone Layer

The ways to conserve, recycle, and replenish natural resources have been included in the important questions Class 9 Science Chapter 14 for students to understand the value of nature. That will help them become better citizens and protectors of our planet earth.

Extramarks provides NCERT textbook, NCERT solutions, NCERT Exemplar, NCERT revision notes, NCERT formulas, NCERT-based mock tests and the Important Questions Class 9 Science Chapter 14 on the official website so that students don’t lack behind in any aspect of their preparation and excel in their examinations with ease.

Get Access to CBSE Class 9 Science Important Questions 2022-23 with Solutions

Also, get access to CBSE Class 9 Science Important Questions for other chapters too:

CBSE Class 9 Science Important Questions
Sr No Chapters Chapter Name
1 Chapter 1 Matter in Our Surroundings
2 Chapter 2 Is Matter Around Us Pure
3 Chapter 3 Atoms and Molecules
4 Chapter 4 Structure of Atom
5 Chapter 5 The Fundamental Unit of Life
6 Chapter 6 Tissues
7 Chapter 7 Diversity in Living Organisms
8 Chapter 8 Motion
9 Chapter 9 Force and Laws of Motion
10 Chapter 10 Gravitation
11 Chapter 11 Work and Energy
12 Chapter 12 Sound
13 Chapter 13 Why Do We Fall ill
14 Chapter 14 Natural Resources
15 Chapter 15 Improvement in Food Resources

Natural Resources Class 9 Important Questions with Answers

The following important questions and their solutions are included in the Science Class 9 Chapter 14 important questions:

Question  1. The atmosphere of earth is heated by radiation which is mainly

(a) radiated by the sun

(b) re-radiated by the land

(c) re-radiated by the water

(d) re-radiated by land and water

Answer  1. 

The answer is (d) re-radiated by land and water


The heat from the sun reaches the earth and its water bodies. This heat is re-radiated by the ground as well as water that heats the atmosphere.

Question  2. When there is no atmosphere around the earth, the temperature of the earth would

(a) increase

(b) go on decreasing

(c) increase during the day and decrease during the night

(d) be unaffected

Answer 2. 

The answer is (c) increase during the day and decrease during the night


Because the atmosphere prevents a lot of heat from reaching the earth’s surface, the atmosphere also prevents the escape of the heat during the night. Thus the atmosphere is responsible for maintaining ambient temperature.

Question 3. What would happen when all the oxygen in the environment is converted to ozone?

(a) We would be protected more

(b) It would become poisonous and kill living forms

(c) Ozone is not stable; hence it would be toxic

(d) It would help harmful sun radiations to reach earth and damage many life forms.

Answer 3. 

The answer is (b) It will become poisonous and kill living forms


All organisms living on earth require oxygen to live. When oxygen is converted to ozone, all living beings will die.

Question 4. One of the following factors doesn’t lead to soil formation in nature

(a) the sun

(b) water

(c) wind

(d) polythene bags

Answer 4. 

The answer is (d) polythene bags


Polythene bags pollute the soil hence making it infertile.

Question 5. The two forms of oxygen found in the atmosphere are

(a) water and ozone

(b) water and oxygen

(c) ozone and oxygen

(d) water and carbon dioxide

Answer 5. 

The answer is (c) ozone and oxygen


Ozone is an allotropic form of oxygen.

Question 6. The process of the nitrogen-fixation by bacteria does not take place in the presence of

(a) the molecular structure of hydrogen

(b) the elemental form of oxygen

(c) water

(d) the fundamental system of nitrogen

Answer 6. 

(b) the elemental form of oxygen

Question 7. Rainfall patterns depend upon

(a) the underground water table

(b) the number of water bodies in an area

(c) the density pattern of the human population in an area

(d) the prevailing season in an area

Answer 7. 

The answer is (b) the number of water bodies in an area


Bodies of water provide water for evaporation, which turns into clouds and brings rain.

Question 8. Among the given option, which one is incorrect for using a large number of fertilisers as well as pesticides?

(a) They are eco-friendly

(b) They turn fields barren after some time

(c) They adversely affect valuable components of the soil

(d) They destroy the soil fertility

Answer 8. 

The answer is (a) They are eco-friendly

Question 9. The nitrogen molecules present in the air can be converted into nitrates and nitrites by

(a) a biological process of the nitrogen-fixing bacteria present in the soil

(b) a natural process of the carbon fixing factor present in the soil

(c) any of the industries manufacturing nitrogenous compounds

(d) plants used as cereal crops in the field

Answer 9. 

The answer is (a) a biological process of nitrogen-fixing bacteria in the soil.


Cereals can’t fix nitrogen on their own. They comprise bacteria into their root nodules which would convert nitrates to nitrites. That process is known as nitrogen fixation.

Question 10. One of the following processes is not a step involved in the water cycle operating in nature

(a) precipitation

(b) transpiration

(c) evaporation

(d) photosynthesis

Answer 10. 

The answer is (d) photosynthesis


Photosynthesis is part of the carbon cycle and not the water cycle.

Question 11. The term “water pollution” can be defined in several ways. Which of the following statements doesn’t give the correct definition?

(a) The addition of undesirable substances to the water bodies 

(b) The removal of desirable substances from bodies of water

(c) A change in pressure for the water bodies

(d) A change in temperature for the water bodies

Answer 11. 

The answer is (c) A change in the pressure of the water bodies


Physical causes lead to changes in pressure on water bodies. Hence the change in water pressure would not affect the quality of water.

Question 12. Which of the following is not a greenhouse gas?

(a) Methane

(b) Carbon dioxide

(c) Carbon monoxide

(d) Ammonia

Answer 12. 

The answer is (d) Ammonia

Question 13. Which step is not part of the carbon cycle?

(a)  Burning of fossil fuels

(b) Transpiration

(c) Respiration

(d) Photosynthesis

Answer 13. 

The answer is (b) Transpiration


 Transpiration is the process of exhaling water from trees. Transpiration is involved in the water cycle.

Question 14. Ozone-hole means

(a) thickening of ozone in the ozone layer

(b) thinning of the ozone layer

(c) small holes scattered in the ozone layer

(d) a large-sized hole in the ozone layer 

Answer 14. 

The answer is (b) thinning of the ozone layer

Question 15. Ozone-layer is getting depleted due to

(a) excessive use of automobiles

(b) excessive formation of industrial units

(c) excessive use of man-made compounds containing both fluorine and chlorine

(d) excessive deforestation.

Answer 15. 

The answer is (c) excessive use of man-made compounds containing fluorine and chlorine.


Carbon and fluorine react with ozone to convert them into oxygen. That results in the thinning of the ozone layer, called ozone depletion.

Question 16. Which of the following is a recent environmental issue?

(a) Global warming

(b) Greenhouse effect

(c) Ozone layer depletion

(d) All of the above

Answer 16.  

The answer is (d) All of the above

Question 17. When we breathe in air, nitrogen and oxygen go inside. What is the fate of nitrogen?

(a) It moves along with the oxygen into the cells

(b) It comes out with CO2 during exhalation

(c) It is absorbed by the nasal cells

(d) Nitrogen concentration is already more in cells. Thus, it is not absorbed.

Answer 17.  

The answer is (b) It comes out with CO2 during exhalation


Nitrogen is the most abundant gas in nature; since, while inhalation, nitrogen goes inside our body along with oxygen. But it is not utilised by our body and is exhaled along with carbon dioxide.

Question 18. Topsoil contains the following

(a) Humus and living organisms only

(b) Humus and soil particles only

(c) Humus, living organisms and plants

(d) Humus, living organisms and soil particles.

Answer 18.  

The answer is (d) Humus, living organisms and soil particles.

Question 19. Choose the correct sequences

(a) CO2 in the atmosphere → decomposers → organic carbon in animals → organic carbon in plants

(b) CO2 in the atmosphere → organic carbon in the plants → organic carbon in the animals → inorganic carbon in soil

(c) Inorganic carbonates in the water → organic carbon in the plants → organic carbon in animals → scavengers

(d) Organic carbon in the animals → decomposers → CO2 in the atmosphere → organic carbon in plants

Answer 19.  

The answer is (b) CO2 in the atmosphere → organic carbon in plants → organic carbon in animals, → inorganic carbon in the soil.


Green plants utilise atmospheric carbon dioxide during photosynthesis to make organic compounds. If animals eat plants, organic compounds will go to animals. When plants or animals die, they decompose into inorganic carbon.

Question 20. Major source of minerals in the soil is the

(a) parent rock from which the soil is formed

(b) bacteria

(c) animals

(d) plants 

Answer 20.  

The answer is (a) parent rock from which soil is formed


Rock weathering is the process which forms soil. Soil is produced from rocks (parent material) through the processes of weathering and natural erosion. Rocks are rich in minerals and so is the soil which is formed from them.

Question 21. The total area of ​​the earth covered by water is 

(a) 75%

(b) 50%

(c) 85%

(d) 60%

Answer 21.  

The answer is (a) 75%

Question 22. Biotic components of the biosphere are not constituted by

(a) producers

(b) consumers

(c) decomposers

(d) air

Answer 22.  

The solution is (d) air


The biotic component of the biosphere comprises living entities, and the air is a non-living component; hence the air is not a biotic component.

Question  23. How do fossil fuels cause air pollution?

Answer 23.  

If we burn fossil fuels, carbon dioxide, nitrous oxide and other chemicals are released, which increase the greenhouse effect as well as contribute to global warming. Nitrous oxide forms smog and results in acid rain.

Question 24. How could we prevent the loss of the topsoil?

Answer 24.  

Loss of topsoil could be stopped by 

1) Afforestation, 

2) Crop rotation, 

3) Counter farming 

4) proper irrigation methods.

Question 25. How is the life of the organisms living in the water affected when water gets polluted?

Answer 25.  

Adding pollutants like fertilisers and chemicals to the water bodies would cause diseases in aquatic organisms. Impurities increase the biological oxygen demand of the microorganisms living in water since the dissolved oxygen in the water reduces drastically.

Question 26. During summer, when you go near the lake, you feel relief from the heat; why?

Answer 26.  

 The water in the lake evaporates, and the vapours produced by evaporation create a cooling effect near the lake. Therefore, we feel relieved from the heat.

Question 27. In coastal areas, wind current move from the sea towards the land during the day; but at night, it moves from the ground to the sea. Discuss the reason.

Answer 27.  

During day time, the land heats more than the sea. That creates low pressure on the ground, and the wind always moves from the region of low pressure to high pressure. Similarly, the land cools faster at night, and the sea remains hot, making the wind move from the sea to the ground.

Question 28. Following are a few organisms

(a) lichen

(b) mosses

(c) cactus

(d) mango tree

Which among the above could grow on stones, and also help in the formation of the soil? Write the mode of its action for making soil.

Answer 28.  

Answers are (a) lichen and (b) mosses


Lichens grow on the rocks and release certain enzymes that promote moss growth. Mosses form clumps of the soil from the rock, resulting in topsoil formation.

Question 29. Both abiotic and biotic factors result in soil formation. List the names of those factors by classifying them as abiotic and biotic.

Answer 29.  

Abiotic factors;

Sun, water and wind

Biotic Factors:

Lichens, mosses and trees.

Question 30. All living organisms are made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.

Answer 30.  

C, N, S, P, H and O enter the living community through plants. Carbon comes through photosynthesis, and nitrogen is obtained through nitrogen-fixing bacteria. Sulphur, and Phosphorus, are absorbed from the soil. Hydrogen, and oxygen, are acquired by water. Animals obtain these nutrients from plants.

Question 31. Why does the percentage of gases such as oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?

Answer 31. 

Humans use these gases for their growth and development. However, these are returned to the environment in one form or another. This process of using natural resources and returning them to nature is called the biogeochemical cycle. Due to the biogeochemical cycle, the proportion of gases such as oxygen, nitrogen and carbon dioxide in the atmosphere remains almost the same.

Question 32. Why does the moon have extreme temperature variations, e.g., from (190°C – 110°C), even though it is at the same distance from the sun as the earth is?

Answer 32.  

Earth has an atmosphere which prevents overheating/ overcooling during the day and the night time respectively. On the other hand, the moon does not have an atmosphere. Hence it is  hotter during the day. The lack of atmosphere on the moon also allows heat to escape at night, which leads to a drastic fall in temperature. Hence it becomes cold at night. Because of this phenomenon, the temperature on the lunar surface varies.

Question 33. Why do people love to fly the kites near the seashore?

Answer 33.  

Near the seashore, the breeze blows during the daytime, which is ideal for flying kites.

Question 34. Why does the Mathura refinery pose problems to the Taj Mahal?

Answer 34.  

The Mathura Refinery releases sulfur oxides that cause acid rain. Acid rain corrodes the Tajmahal marble; Therefore, the Mathura refinery is posing problems for Tajmahal.

Question 35. Why can’t we find as many lichens in Delhi as in places like Manali or Darjeeling?

Answer 35.  

Lichens are sensitive to the Sulphur oxide released by automobiles. Delhi has a wide number of vehicles which emits pollution. Due to the poisonous gasses present in automobile pollution, insects like Lichens cannot survive. 

Question 36. Why does water needs conservation even though large oceans surround the landmasses?

Answer 36.  

Sea water is not suitable for human usage or plant nutrition. Freshwater resources are limited. Thus they need to be conserved.

Question 37. There is mass mortality of the fish in a pond. What may be the reasons?

Answer 37.  

Reasons for mortality of the fish in a pond are i) Thermal pollution, ii) the addition of mercuric compounds and other toxic chemicals iii) the Blockage of gills by the pollutants.

Question 38. Lichens are called pioneer colonisers of the bare rock. How could they help in the formation of the soil?

Answer 38.  

Lichens release enzymes to break the rock into smaller pieces and help form soil.

Question 39. “Soil is formed by water.” when you agree with this statement, then give reasons

Answer 39.  

Water causes soil formation by following steps.

  1. Water wears off the rock over an extended period.
  2. As water flows it rubs between the rocks and the rocks get covered into smaller particles deposited as soil.
  3. On a freezing, water expands to cause cracks in the rock.

Question 40. Fertile soil has lots of humus. Why?

Answer 40.  

Fertile soil has several microorganisms that decompose dead and organic matter to convert to humus. Humus provides nutrients, absorbs water and makes soil porous.

Question 41. Why is step farming common in the hills?

Answer 41.  

In hills, steep slopes can lead to the washout of topsoil by wind and rain. To conserve the topsoil, step farming is done in the mountains.

Question 42. Why are root nodules beneficial for plants?

Answer 42.  

Root nodules are the home of nitrogen-fixing bacteria called Rhizobium. Rhizobium fixes atmospheric nitrogen, thereby increasing soil fertility.

Question 43. How do fossil fuels cause air pollution?

Answer 43.  

Fossil fuels like petrol, diesel and kerosene release oxide of sulphur, nitrogen and carbon. Sulphur, and Nitrogen oxides, cause acid rain.

Burning fossil fuels releases carbon monoxide, which increases the carbon-di-oxide in the atmosphere, affecting living organisms.

The burning of fuels increases the number of suspended particles in the air, reducing visibility.

Question 44. What are the causes of water pollution? Discuss the measures to be taken to reduce it. . 

Answer 44.  

The causes of water pollution are given below.

  1. Chemical Fertilisers and pesticides consist of poisonous chemicals which reach the water body turning it toxic.
  2. Dumping of sewage directly into the water bodies
  3. Release of industrial effluents into the water resources.

Below are the steps we could take to reduce water pollution

  1. Stop connecting sewage lines directly to the water bodies.
  2. Avoid throwing garbage and other domestic waste into the water resource.
  3. Prevent dumping of toxic chemicals into the water body.
  4. Avoid washing clothes near water bodies.

Question 45. A motor car, with its glass closed, is parked directly under the sun. The inside temperature of the car rises very high. Explain why.

Answer 45.  

Infrared radiation emitted by the sun can pass through the transparent glass and increase the temperature inside the car. These radiations have smaller wavelengths than the radiations emitted by the vehicle. For these waves, transparent glass remains opaque, further increasing the temperature.

Question 46. Justify “Dust is a pollutant”?

Answer 46.  

Dust is the fine powder of tiny earth particles and waste matter. It is carried into the atmosphere by the wind. Dust causes allergy in humans as well as affects plant growth by blocking the stomata on the leaf surface. Thus, dust also carries toxic substances from the environment to pollute water bodies affecting aquatic life.

Question 47. Explain the role of the sun in soil formation.

Answer 47.  

Sunlight heats the rock in the afternoon, causing the rock to expand. When it cools down at night, contraction occurs, which is not at the expansion rate. Because of that difference in the rate of expansion and contraction, the rock gets cracked to form small rock particles.

Question 48. Carbon dioxide is necessary for plants. Why do we consider it a pollutant?

Answer 48.  

Carbon dioxide is a pollutant because, as a greenhouse gas, it is responsible for global warming. This leads to a change in the earth’s climate. In addition, excess CO2 is harmful to plants. Increasing CO2 concentrations change the physiology, growth and chemistry of plants. The high concentration of CO2  also causes suffocation, and breathing difficulties. 

Question   49. How is our atmosphere different from the atmospheres of Venus and Mars?

Answer 49.   

Earth’s atmosphere is composed of various gases like oxygen, carbon dioxide, nitrogen, and water vapour, along with multiple gases in small quantities, therefore making it a balanced composition which is more livable than other planets. Planets like Venus and Mars have more than 95% of carbon dioxide in the air making the existence of life impossible.

Question 50. How does the atmosphere act like a blanket?

Answer 50.  

⇒ It maintains consistency in temperature throughout the day, making it a comfortable place to stay.

⇒ The ozone in the atmosphere is responsible for maintaining the temperature without letting the harmful ultraviolet rays affect it.

Question 51. What causes winds?

Answer 51.  

The uneven heating of the earth’s surface is the main cause of winds. The air rises on being heated, so low pressure is created. Hence, the air in high pressure occupies the low-pressure region causing the wind to flow.

Question 52. How are clouds formed?

Answer 52.  

During the daytime, in the presence of sunlight, water from sources like well, lakes, ponds, sea, rivers and various other sources evaporate, and these water vapours rise with the hot air. At a particular height, the air cools, and water vapour condenses to form minute droplets to form clouds.

Question 53. List three human activities that you think would lead to air pollution.

Answer 53.  

⇒ Burning of fuels like petroleum, kerosene, and coal in the atmosphere

⇒ smoke released from manufacturing industries

⇒ Smoke from vehicles

Question 54. Why do organisms need water?

Answer 53.  

Organisms need water for

⇒  To help in the cellular processes 

⇒ To help in the process of Photosynthesis in the plants

⇒ Transportation of substances in the body takes place through water by dissolving the contents in the water.

⇒ Required minerals are transported in Terrestrial animals through water.  

⇒  To eliminate waste from the body.

Question 54. What is a significant source of freshwater in the city/town/village where you live?

Answer 54.  

⇒ Rainfall

⇒ Underground water from wells

⇒ Water sources like ponds, rivers, and lakes

⇒ Snowfall

Question 55. Do you know of any activity polluting this water source?

Answer 55.  

⇒ Dumping waste in the river

⇒ Factory waste

⇒ Sewage

Question 56. What are the different states where water is found during the water cycle?

Answer 56.  

Water is found in the three states like

⇒ A solid state (Snow, ice)

⇒ Liquid state (river water, underground water)

⇒ Gaseous state (water vapour)

Question 57. Name two biologically important compounds which contains both oxygen and nitrogen

Answer 57.  

⇒ DNA (Deoxyribonucleic Acid)

⇒ RNA (Ribonucleic Acid)

⇒ Amino acids

Question 58. List any three human activities which will lead to an increase in the carbon dioxide content of the air

Answer 58.  

⇒ Breathing process where Carbon dioxide is released

⇒ Burning of petrol, coal, and fuel

⇒ Using fridge, air conditioners and oven

Question 59. What is the greenhouse effect?

Answer 59.  

Gases like Carbon dioxide as well as methane trap the sun’s radiation and do not allow it to go back, causing warming of the atmosphere and the greenhouse effect.

Question 60. What are the two forms of oxygen found in the atmosphere?

Answer 60.  

Oxygen is present in two forms

⇒ Diatomic molecular form (O2)

⇒ Triatomic molecular form (O3)

Question 61. Why is the atmosphere essential for life?

Answer 61.  

⇒ The atmosphere comprises various leading gases like O2, N2, and CO2, which are the basis of living microorganisms, plants and animals.

⇒ Photosynthesis occurs due to the earth’s atmosphere 

 ⇒ The consistent temperature of the earth is the cause of the earth’s atmosphere 

 ⇒ Processes such as respiration and combustion are due to the atmosphere 

 ⇒ The atmosphere is the main reason for preventing UV radiation to enter the earth’s surface 

Question 62. Why is water essential to life? 

 Answer 62.  

 ⇒ All biological activities, respiration, digestion and other biological reactions are sustained by water 

 ⇒ Living things are composed of more than 70% water 

 ⇒ The transport of matter from one form to another occurs due to the presence of water. 

Question  63. Write a note about how forests affect the quality of our air, soil, and water resources.

Answer 63.  


  • Forests help in purifying air by absorbing all kinds of pollutants.
  • Forests help increase the oxygen level in the air by absorbing carbon dioxide during photosynthesis.
  • Transpiration help to maintain the temperature of the surroundings and helps in the formation of clouds.


  • Plants in forests hold the soil, thereby preventing soil erosion.
  • Adds nutrients to the soil as much vegetation in the forest gets decomposed.


  • Forest helps bring rain and increase the water level underground.

Question 64. How does the sun help to break down rocks into smaller pieces to form soil? 

Answer 64.  The sun heats and expands up the rock during the day. At night, that rock cools and shrinks. Because not all parts of the rock expand as well as a contract at the same rate. As a result, massive cracks form and break into smaller pieces.

Question 65. What is the composition of air?

Answer 65.  The air has the following components:

Sr. No. Name of gas Percentage composition of gas by volume Percentage composition of gas by mass
1. Nitrogen 78.09 75.5
2. Oxygen 20.95 23.2
3. Argon 0.93 1.0
4. Carbon dioxide 0.031 0.046
5. Neon  0.002 0.0005
6. Helium Negligible Negligible

In addition to the gases, water vapours are also in the air.

Question 66. How does soil pollution occur?

Answer 66.  Soil pollution occurs in the following ways: 

  1. Using high amounts of fertilisers and pesticides kills the microorganisms that help recycle the soil’s nutrients. 
  2. Earthworms that create humus and fertilise the soil are also getting killed with increased use of pesticides.
  3. Addition of harmful substances and removal of valuable components also affect soil fertility.

Question 67. Define smog and the process of its formation.

Answer 67.  Smog – Smog is the combination of smoke and fog.

Formation of the smog – Smog is formed when air pollution exists, and a high level of smoke is therein the atmosphere. That smoke gets mixed with the fog forming smog.

Question 68. What is the importance of water in life?

Answer 68.  Water is essential for life because

  1. All life processes occurring inside the cell occur in a water medium.
  2. Transportation of various substances in the body occurs through water.
  3. Transportation of various substances in the plants also occurs through the water.

Question 69. How do living things cause erosion of the rocks? 

Answer 69.  When growing on the surface of the rock, organisms such as lichens release certain chemical substances that cause crushing of the rock’s surface, breaking it down into fine particles.

Question 70. What is the process of rain formation? 

Answer 70.  Water vapours are formed when water from the water bodies evaporates. These water vapours move up in the atmosphere and condense to form tiny water droplets. If a vast amount of water droplets are collected, it becomes a giant water droplet and  becomes heavy, which results in the occurrence of rain.

Question 71. How is earth’s atmosphere different from Venus and Mars? 

Answer 71.  The air present on earth is mainly a mixture of many gases like nitrogen (78%), oxygen (21%), and carbon dioxide (0.03%). However, on planets like Venus and Mars, that has been observed that carbon dioxide is the major component of its atmospheric air. It has been found that carbon dioxide is 95-97% in the atmosphere of Venus as well as Mars.

Question 72. Why is the atmosphere considered a blanket? 

Answer 72.  Because air is a lousy conductor of heat, an atmosphere that covers the earth is like a blanket. The atmosphere stabilises the earth’s average temperature during the day and throughout the year. The atmosphere prevents rapid temperature rises during the day and slows the rate at which heat goes into space at night.

Question 73. How is the wind created? 

Answer 73.  Due to heated land or water, the air over their surface gets heated up and rises. The air over land gets rapidly heated up compared to the air present over water because the ground gets heated faster than the water. Therefore, the atmosphere on land heats up faster during the daytime and begins to rise. If this air rises, a low-pressure region is created, and  the air above the sea moves to the low-pressure area. The wind is created due to air movement from one part to another.

Question 74. What is the process of cloud formation? 

 Answer 74.  A large amount of water evaporates into the air as bodies of water warm during the day. Other biological activities also cause the movement of the water in the atmosphere. Along with the water vapours, the air gets heated and rises. If the air rises, it expands and cools. The cooling causes condensation of the water vapours and converts them into droplets. This water condensation is facilitated when some particles can act as the “nucleus” around which these droplets can form. In general, dust in the air, as well as other suspended particles, act as nuclei. This process creates clouds.

Question 75. Write down human activities that are responsible for causing air pollution.

Answer 75.  The given human activities could cause air pollution:

  1. Combustion of the fossil fuels such as coal or petroleum releases various nitrogen and sulphur oxides into the air.
  2. Smoke and other suspended particles are released into the air due to the burning of wood.
  3. Usage of harmful chemicals like aerosols, CFCs, etc., could cause air pollution.

Question 76. What is the need for water for living organisms?

Answer 76.  Living organisms require water to perform the various life processes. All living things are made up of cells, and all cellular processes take place in water. The chemical reactions occur in living cells between the compounds dissolved in water. Also, the transportation of various substances occurs from one part of the body to another in dissolved form. Therefore, living organisms must maintain their bodies’ water levels to stay alive.

Question 77. What are freshwater sources in different places on earth?

Answer 77.  Following are some freshwater sources found in the different places on earth:

  • Ponds
  • Lakes
  • Rivers
  • Wells and Tubewells
  • Dams
  • Rainwater provides water to all of the above freshwater sources.

Question 78. Do you know about activities that could pollute freshwater sources? 

Answer 78.  We use fertilisers and pesticides on our farms. Their excess use could pollute these water sources. The sewage in our towns and cities, waste from factories, and water used for cooling in various operations in specific industries are released into these water sources. Such activities pollute the water bodies.

Question 79. What is the process of soil formation?

Answer 79.  Over a long time, like millions of years ago, the rocks on earth were weathered by various physical, chemical and biological factors. That weathering resulted in the formation of soil particles. Factors responsible for weathering of rocks and the construction of soil are given below:

The Sun: The sun’s heat radiation causes the rocks’ expansion. These rocks cool down at night and contract, thus, forming cracks in the rocks.

Water: Water supports two methods by which soil formation takes place. First, water could enter cracks of rock formed due to uneven heating by the sun. Then, later on, this water freezes and causes damage to spread.

Wind: Strong winds rub against rocks and erode them down in a similar way to that of water.

Living organisms: Some living organisms release a chemical that causes the crushing of the rocks. Lichens are organisms that grow on stones and  release some chemicals that convert the rocks into soil particles. Some other plants like mosses grow on the rocks and create cracks as their roots penetrate the rocks.

Question 80. By which methods can soil erosion be reduced or prevented?

Answer 80.  By applying the following methods, soil erosion could be reduced or prevented:

  • Deforestation and overgrazing of the animals should be reduced.
  • More trees shall be planted to support afforestation or reforestation.
  • The agricultural method should be improved.

Question 81. What is the role of the atmosphere in making life possible on earth?

Answer 81.  The atmosphere is essential for life in the following ways:

  • It protects the living organism from harmful sun radiations by acting like a blanket that covers the earth’s surface and traps the harmful UV radiations from the sun. In this way, the atmosphere also maintains a constant earth temperature.
  • The atmosphere provides carbon dioxide for photosynthesis and oxygen for respiration and combustion.
  •  A sudden change in the earth’s temperature is prevented by the atmosphere.

Question 82. What is the role of water in making life possible on earth?

Answer 82.  Water is essential for all types of life forms because:

  • All living organisms comprise living cells, and various kinds of cellular processes that occur in water mediums. All types of metabolic reactions occur in living organisms, and their cells occur between the substances dissolved in water.
  • Transportation of substances that occur in the living organisms takes place in dissolved form.
  •  Water is required in digestion, excretion, as well as egestion-like body processes.
  • Water regulates the body temperature of the organisms by sweating.

Question 83. How do living things depend on soil? Are the organisms living in water completely independent of the earth as a resource? 

Answer 83.  Plants require simple nutrients, like certain elements, to grow normally, most of these elements are obtained from the soil. Plants use these elements to prepare their food in the presence of the sun. Because all other living things depend on plants for their development and diet, we could say that organisms living in the water are not entirely independent of the soil as a resource. Another reason is that the organic matter in soil is dissolved in the water to provide nutrients for the aquatic organism. 

Question 85. Many human activities lead to increased air, water, and soil pollution. Do you think isolating these activities in restricted and enclosed areas will help reduce pollution?

Answer 85.  Isolating many human activities this cause an increase in air, water, and soil pollution will help reduce water and soil pollution. Still, it is unlikely to affect the severity of air pollution because gases can spread quickly from the transmission area to other places nearby. We need to focus on sustainable management of the resources, rather than isolate them, and reduce or replace their consumption, like using clean fuels like CNG to replace fossil fuels. 

Question 86. Explain how forests affect the quality of the air, water, and soil resources.

Answer 86.  Effects of forests on air: Trees, and plants in the woods, can absorb carbon dioxide and  release oxygen, thereby maintaining the level of these gases in the biosphere.

Effects of forests on the water: Forests enable the water cycle in nature to form clouds which  condense to cause rainfall.

Effects of forests on the soil: The roots capture soil particles and prevent soil erosion. Dead trees and plants or parts enrich the soil with humus as well as organic matter, making them fertile.

Question 87. Write down the biotic and abiotic factors that cause soil formation.

Answer 87.  Some of the abiotic factors this cause soil formation are given below:

  • The Sun: The sun’s heat radiation causes the rocks’ expansion. These rocks cool and shrink at night, causing cracks in the rocks. 
  •  Water: Water supports two methods by which soil formation occurs. First, water could enter cracks of rock formed due to uneven heating by the sun. And later on, this water freezes and causes cracks to spread.
  •  Wind: Strong winds rub against rocks and erode them down in a similar way to that of water.

Biotic factors responsible for soil formation:

Some living organisms release chemicals that cause the crushing of the rocks. Lichens are organisms that grow on the rocks and release some chemicals that convert the stones into soil particles. Some other plants like mosses grow on the rocks and create cracks as their roots penetrate the rocks. 

Question 88. Mention some sources that cause air pollution.

Answer 88.  The given sources can cause air pollution:

  • Some natural processes like forest fires can cause air pollution, smoking volcanoes, sandstorms, floating pollen particles, and organic degradation.
  • Consequences of some human activities like overpopulation, deforestation, urbanisation and industrialisation.  
  • The burning of fossil fuels in automobiles, thermal power stations and industries cause air pollution.

Question 89. Why is the Mathura refinery a problem for the Taj Mahal?  

Answer 89.  The Mathura refinery emits acidic gases such as sulphur and nitrogen dioxide into the air. In the presence of moisture, sulphur dioxide is oxidised to sulfuric acid, and nitrogen dioxide is oxidised to nitric acid in the air. . Acid rain is the rainwater that contains acid as a pollutant. This acid rain turned the white marble of the Taj Mahal pale.

Question 90. How does the atmosphere function as a protective blanket? Can you mention the harmful effects of ultraviolet light?  

Answer 90.  The atmosphere protects the earth as it absorbs the most harmful radiation, such as ultraviolet radiation from the sun. The deadly radiation is absorbed by the upper atmosphere and reflected into space. The sun’s rays are reflected in the area by dust particles, water vapour, and clouds. Because of this, the earth receives the necessary heat and light from the sun, which helps control the weather and allows living things to survive. The harmful effects of UV radiation can cause blindness and diseases such as  skin cancer.

Question 91. Explain the reasons:  

  1. a) Step farming is prevalent in the mountain.   

Answer 91.  On a hilly slope, step farming reduces the steepness of the hill thus controlling soil erosion.  

  1. b) Fertile soil contains a lot of hummus. 

Answer 91.  The decomposition of the dead organic matter occurs in the topsoil. This monastery, built-in, converts organic materials into hummus. Therefore, fertile soil has hummus.

Question 92. What are the hazards of air pollution?  

Answer 92.  The Harmful Effects of Air Pollution are:

  • Air pollution affects the respiratory tract of living things, causing bronchitis,  pneumonia, asthma, and lung cancer.  
  • Burning fossil fuels such as coal and patrols releases nitrogen oxides and sulphur and cause acid rain.  
  • Burning fossil fuels like coal and petroleum would also increase particulate matter in the air. The presence of those pollutants in the air during the cold season could cause the formation of smog, which reduces visibility as well as causes traffic problems.

 Question 93. Most of the land is surrounded by sea. Then why do we need to save water?  

Answer 93.  Though most of the land is covered by water but as a fact, there are very few sources of fresh water which is appropriate for human usage. Hence, it becomes important to conserve those sources. Some of the other reasons are given as follows: 

  1. Due to the growth of the population, water consumption is increasing substantially.  
  2. Due to the increase in water pollution, the sources are becoming inappropriate for human usage, hence causing a shortage of water.  
  3. The groundwater level has fallen down due to overuse. 

Question 94. What is weathering? How does weathering happen?  

Answer 94.  The formation of the soil due to the destruction of rocks is called weathering. It is derived from  

  • physical factors including the sun (temperature), rain, wind, and frost.  
  • Biological media-through the action of plants, animals and microorganisms.

Question 96. “Water is important.” Give the reason for the statement.  

Answer 96.  The value of the water of life is explained in the following points:

  • It acts as the universal solvent.  
  • Most of the activities for the body are carried out in the water.  
  • Transfer of the substance from one part of the body to another in a dissolved form.
  • Dissolve waste and promote excretion from the body.  
  • Aquatic organisms use oxygen dissolved in water.

Question 97. How do forests affect our water, air,  and soil? 

Answer 97.  Forests affect air, water, and soil in the following ways:

  • The forest acts like an air purifier. During photosynthesis, they consume carbon dioxide and release oxygen.  
  • The forest also keeps water levels below ground level. The roots absorb water as well as raise the water level. Trees also contribute to cloud formation during evaporation and increase the air’s humidity (water vapour). This water vapour will form more clouds, which will help when it rains. 
  • Tree roots support the soil and prevent erosion, thereby maintaining soil fertility.

Question 98. What is the greenhouse effect? How does this affect the earth’s atmosphere?

Answer 98.  Increasing the concentration of water vapour and other atmospheric gases (such as nitrous oxide methane) will prevent the release of solar radiation. That increases the atmosphere’s temperature above the earth’s surface, making it warmer. This phenomenon is called the greenhouse effect. The atmosphere would melt snow from the polar and high mountains, rising sea levels and low-lying flood areas.

Question 99. What are the hazards of water pollution?  

Answer 99.  The hazards of water pollution are as follows:  

  • Polluted water could cause water-borne diseases like dysentery, cholera and jaundice.  
  • Pesticides like DDT enter the water body with rainwater and, from there, enter the food chain through producers and accumulate at various trophic levels. This is called a biological surge, which seriously affects the body at the top of the food chain.  
  • Eutrophication-Excessive phytoplankton growth due to wastewater discharge will reduce the level of dissolved oxygen, thereby affecting the aquatic organisms.

Question 100. What is a biogeochemical cycle? How is the nutrient cycle in the atmosphere? 

 Answer 100.  The cycle of nutrients between the inanimate environment (soil, air, water) and living organisms is called the biogeochemical cycle.

 Where i) shows the ammonification process while ii) shows denitrification. 

Question  101. Explain how you can reduce the concentration of carbon dioxide in the atmosphere. 

 Answer 101.  Ways to Reduce Carbon Dioxide Concentration- 

  1. a) Photosynthetic plants absorb carbon dioxide from the air and use it to synthesise food. 
  2. b) Fossils: Earth’s pressure and temperature convert dead plants and animals into fossil fuels such as coal and oil. 
  3. c) The carbon dioxide in the water combines with the carbonate and graphite in the rock. 

Question  102. How do fossil fuels pollute the air? 

 Answer 102.  The burning of fossil fuels has the following effects: 

  1. a) When burning fossil fuels, nitrogen oxides are released in addition to sulphur. This could lead to respiratory problems and acid rain. 
  2. b) The burning of fossil fuels increases the amount of particulate matter in the air, which can cause smog, impaired visibility and traffic accidents in winter. 
  3. c) When burned, it emits carbon dioxide, which absorbs solar energy and raises the temperature of the earth. 

Question  103. Write down what happens when the water becomes contaminated. 

 Answer 103.  When water becomes polluted, the following events occur: 

  1. a) Undesirable substances that could cause cholera are added to water bodies. 
  2. b) It could remove required substances from water bodies and dissolve oxygen, which is important for aquatic organisms and poses a danger to marine organisms.  
  3. c) if water is polluted, the water’s temperature will change, adversely affecting the life forms in water.

Question 104. Do you write about the nitrogen cycle in nature? 

 Answer 104.  The nitrogen cycle is divided into the following stages: 

  1. a) Atmospheric nitrogen is converted into the protoplasm of green plants by nitrogen fixation. 
  2. b) The protoplast is converted into ammonia by ammonia.
  3. c) Ammonia then converts to nitrite and then to nitrate. 
  4. d) Nitrogen in the atmosphere is then directly converted to nitrate by nitrification. 
  5. e) Nitrate is converted to nitrogen by denitrification. 

Source: Internet

Question  105. What is the greenhouse effect? What happens when the amount of carbon dioxide in the air increases?

Answer 105.  The greenhouse effect is the phenomenon in which various gases absorb heat in the air and cause the earth’s temperature to rise. When the carbon dioxide content in the air grows because carbon dioxide is a greenhouse gas, the greenhouse effect will increase and cause the earth’s atmospheric temperature to rise rapidly. That leads to the melting of glaciers and becoming a danger for various living organisms.

Question 106. What role does ozone play in the atmosphere? How is the ozone hole formed? 

 Answer 106.  The ozone layer absorbs harmful radiation from the sun, preventing it from reaching the earth’s surface, where it can harm living things. There are ozone layers, just as an ozone hole was discovered over Antarctica. 

Question  107. What role does the soil play in agriculture? 

 Answer 107.  Soil is the loose surface material that covers most land. It consists of inorganic particles and organic matter. Soil is the breeding ground for all plants. It provides material support, nutrients for plant growth, and adequate air and water. 

Question  108. What is the difference between the earth’s atmosphere and the atmospheres of Venus and Mars? 

Answer 108.  The earth’s atmosphere is a mixture of gases consisting mostly of nitrogen and oxygen, and a small amount of carbon dioxide, water vapours and other gases. This presence of gases makes the existence of life possible on earth. However, the atmosphere of Venus and Mars is mainly composed of carbon dioxide. So the possibility of having life on Venus and Mars is not there.

Question 109. What is air pollution, and how does it cause acid rain? 

Answers 109. The air is mixed with pollutants, altering the components of the air in a way that makes it harmful, known as air pollution. If fossil fuels such as coal and oil are burned, various oxides of nitrogen and sulfur are produced, which mix with rainwater to form nitric acid and sulfuric acid, and then fall to the surface of the earth as rain acid. It is very dangerous because it can disrupt living organisms and destroy buildings and monuments. 

Question 110. Why is carbon dioxide so important for the survival of life on earth? What two methods are there to attach it to the ground? 

 Answer 110.  Carbon dioxide contributes to the warming of the earth’s surface, which helps maintain a suitable temperature for life forms on earth. It is also necessary for photosynthesis in plants.

 It fixes in two ways: 

 (a) Green plants convert to glucose in the presence of sunlight. 

 (b) Marine animals use carbonates dissolved in seawater to make shells.

Benefits of Solving Class 9 Science Chapter 14 Important Questions

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Q.1 Identify the different components of the given cycle and name the cycle represented here.


The different parts of the cycle are:

1 = Sun

2 = Clouds

3 = Evaporation

4 = Precipitation/Rain

5 = Ocean

The cycle represented here is a water cycle.

Q.2 Why does the average temperature on earth remains fairly steady?


Atmosphere acts as a blanket and prevents the extreme fluctuation of temperatures. Average temperature on earth remains fairly steady because air is a bad conductor of heat. The atmosphere slows down the escape of heat into outer space during night and prevents the sudden increase in temperature during day time.

Q.3 What function does the atmosphere play in regulating the climate?


The atmosphere keeps the average temperature of the earth fairly steady during the day and even during the course of the whole year. The atmosphere prevents the sudden increase in temperature during the daylight hours. And during the night, it slows down the escape of heat into outer space.

Q.4 Name the outer layer of the earth.



Q.5 Write the name of two organisms, which take part in the nitrogen fixation.


Rhizobium and Azotobacter.

Q.6 Define hydrosphere.


All the water present on earth is called as hydrosphere. Water covers 75% of the earth’s surface.

Q.7 Draw a neat and clean diagram of C-cycle.


Q.8 What are the various methods to control pollution?


The methods to control pollution are:
(i) Conversion of organic waste and faecal material into compost.
(ii) Dumping of non-degradable waste in low lying areas.
(iii) Proper disposal of sewage.
(iv) Installation of gobar gas plants.
(v) Growing of plants capable of fixing carbon monoxide and nitrogen oxides.
(vi) Use of CNG in automobile

Q.9 Describe the nitrogen cycle.


Nitrogen is an essential nutrient for all life-forms and life. However, other than a few forms of bacteria, life-forms are not able to convert the comparatively inert nitrogen molecule into forms like nitrates and nitrites which can be taken up and used to make the required molecules. 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 temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various lifeforms.
Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins. Some other biochemical pathways are used to make the other complex compounds containing nitrogen. These proteins and other complex compounds are subsequently consumed by animals. Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. A different type of bacteria converts the nitrates and nitrites into elemental nitrogen.

Q.10 What is atmosphere?


The air that covers the whole of the earth is called atmosphere.

Q.11 What is the percentage of CO2 on Venus?



Q.12 Define combustion.


The process, which results in the consumption of the oxygen and production of carbon dioxide and energy is called combustion.

Q.13 What is the role of ozone layer?


Ozone layer protects us from UV rays.

Q.14 What will happen if the CO2 concentration in the atmosphere increases?


The temperature of earth will increase.

Q.15 Define nitrogen fixation.


The conversion of atmospheric nitrogen into compounds that plants and other organisms can assimilate is called nitrogen fixation. This is done by certain soil microorganisms, such as Rhizobium.

Q.16 How can you describe global warming?


The gradual increase in the temperature of the earth’s atmosphere, believed to be due to the greenhouse effect, caused by increased levels of carbon dioxide, chlorofluorocarbons, and other pollutants.

Q.17 What are the biotic and abiotic components?


Living things such as animals and plants constitute the biotic component of the earth, while the non living things such as the air, water and soil form the abiotic component.

Q.18 What are the modes of CO2 fixation?


(i) Green plants convert CO2 into glucose in the presence of sunlight. This process is called photosynthesis.
(ii) Many marine animals use carbonates dissolved in sea-water to make their shells.

Q.19 Define biosphere.


The part of the earth and its atmosphere in which living organisms exist or that is capable of supporting life is known as biosphere.

Q.20 How can you decide whether a given sample of water is polluted or non-polluted?


When there is any physical, biological or chemical change in water which adversely affects living organisms and makes it unfit for use, it is called as polluted. Water contamination can be detected by the smell or sight of the water. The smell of rotting eggs emanates from water contaminated with sulphur or certain bacteria.

Q.21 Define humus and give its function.


A brown or black organic substance consisting of partially or wholly decayed plant or animal matter is called humus. It provides nutrients for plants and increases the ability of soil to retain water.

Q.22 What are pollutants? Give the different types of the air pollutants with example.


The agents which cause pollution are called pollutants. Different type of pollutants are as follows

  • Gaseous pollutants: – Sulphur dioxide, nitrogen peroxide, etc.
  • Particulate pollutants: – Carbon particles, dust, etc.

Q.23 Draw the labelled diagram of the O2 cycle.


Q.24 Why do organisms need water?


Water is required by organisms to maintain numerous life processes. In addition, water is a necessary component of all living organisms. All cellular processes take place in water medium. Moreover, the substances are transported from one part of the body to the other in the dissolved form.

Q.25 Define ammonification and nitrification.


Ammonification: – The conversion of organic material of the plants and animals into ammonia
Nitrification: – The conversion of atmospheric nitrogen into nitrates

Q.26 Describe the factors or processes that make the soil.


The factors that contribute to the soil formation are as follows

  • Sun : Responding to the temperature variation during day and night, all parts of the rock do not expand and contract at the same rate, resulting in the formation of cracks and ultimately the rocks break.
  • Water : On freezing the water accumulated in the cracks of rocks starts expanding, resulting in the broadening of cracks and ultimately the rocks break. Fast flowing water wears away rocks.
  • Wind : Strong wind rubs against rocks and wears them down.
  • Living organisms : Lichens while growing on the surface of the soil release certain substances that cause the rock surface to powder down and form a thin layer of soil.

Q.27 Describe the wind movement in the coastal regions.


The situation in coastal regions during the day the air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land. At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land. Thus during night, movement of wind would be from land to sea.

Q.28 Describe the process which results in rain.


When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it. 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. This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function. Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.

Q.29 Describe the effects of the air pollution.


When fossil fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur. Not only is the inhalation of these gases dangerous, they also 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 of hydrocarbons. Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution. Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.

Q.30 State any three cause of water pollution.


The three cause of water pollution are as follows
(i) Agricultural substances like fertilizers and pesticides are used to increase crop yield, and some percentage of these is washed into the water bodies that pollute the water.
(ii) Sewage from homes and wastes from factories are dumped into rivers or lakes, ultimately polluting the water.
(iii) Hot and cold water discharged from industries also contribute to water pollution. These result in a change in temperature which is harmful for aquatic organisms.

Q.31 Define photosynthesis, which gas is released as its by-product?


Photosynthesis is the production of food (carbohydrates) by plants from carbon dioxide and water in the presence of green pigment called chlorophyll, using energy, captured from sunlight and releasing of excess oxygen as a by-product.

Q.32 How is Earth’s atmosphere different from that of Venus and Mars?


In Earth’s atmosphere CO2 is 0.03% and in Mars and Venus, it is 95-97%.

Q.33 At what stage water is said to be polluted?


When there is any physical, biological or chemical change in water that adversely affects living organisms and makes it unfit for use, it is called polluted.

Q.34 Mention the cause of green house effect.


Greenhouse effect is caused by gases in the atmosphere that have the ability to absorb sun’s energy. The ‘greenhouse gases’ allow short-wave radiations to pass through to the earth, but absorb the long-wave radiations that are reflected back to space. These gases include carbon dioxide, methane, water vapour, nitrous oxides, CFCs etc. An increase in the percentage of these gases in the atmosphere causes increase in average temperature of earth, known as greenhouse effect.

Q.35 Explain oxygen cycle in nature with diagram.


Oxygen is required for respiration by all the living organisms. Oxygen oxidizes the food materials and produce energy and carbon dioxide. The carbon dioxide is utilized by the plants to produce food materials during the process of photosynthesis. The free oxygen released in photosynthesis is again used in respiration or it may return to environment as molecular oxygen.

Q.36 Complete the boxes with appropriate natural resources and define the zone that comprises of all the three forms of life.


The biosphere is the life supporting zone of earth where all 3 forms of life – air, land and water co-exists.

Q.37 Name the man-made component which is responsible for the depletion of ozone layer.


CFC (Chloro Fluoro Carbon).

Q.38 How is ‘humus’ formed?


‘Humus’ is the organic constituent of soil formed by complete or partial decomposition of plant and animal materials.

Q.39 Mention two methods through which living organisms influence the formation of soil.


1. Roots of big trees penetrate into the crevices of rocks and enhance rock-breaking process.
2. Lichens, bryophytes (mosses) release some substances causing powdering of rock surfaces.

Q.40 Explain how water is useful to living organisms.


1. All cellular processes take place in water medium. The reactions that take place within our body inside the cells occur between substances that are dissolved in water.
2. Water is a very good solvent. Also, substances are transported from one part of the body to the other in dissolved form.

Q.41 a) What is symbiosis?
b) Name a symbiotic life form.


a) Symbiosis is the relation between two different species of organisms that are interdependent; each gains benefit from the other.
b) A symbiotic life form— Lichen (association of a fungus and an alga)

Q.42 a) Mention two ways of mode of fixation of CO2.
b) Mention three ways by which carbon returns to the C-cycle.


a) Mode of fixation of carbon-di-oxide:
(i) Green plants convert CO2 into glucose in the presence of sunlight. This process is called photosynthesis.
(ii) Many marine animals use carbonates dissolved in sea-water to make their shells.

b) (i) Both plants and animals release carbon dioxide to the atmosphere as a product of respiration.
(ii) By decomposition of organic wastes and dead bodies via decomposers.
(iii) By burning of fossil fuels like coal and petroleum.

Q.43 Explain water or hydrological cycle in the nature with diagram.


The water cycle is a series of activities or processes that transport water between the earth’s seas, atmosphere, and land, including precipitation as rain and snow, drainage in streams and rivers, and evaporation and transpiration, as shown below in the diagram.

Q.44 Mention any two human activities which would be responsible for air pollution.


1. Increased use of vehicles run by fossil fuels raises the gaseous air pollutants.
2. Factory outlets, low efficiency engines throw exhaust gases in the air.

Q.45 Give one visible indication of air pollution.


Formation of smog is a visible indication of air pollution. Presence of high level of pollutants such as hydrocarbons causes visibility to be lowered, especially in cold weather when water also condenses out of air. Increase in the content of these harmful substances in air causes air pollution.

Q.46 What do you understand by fixed nitrogen?


Fixed nitrogen is more stable form of nitrogen, e.g., ammonia or nitrate. Ammonia is formed by biological fixation of nitrogen and nitrate is the product of high energy fixation by lightning or cosmic radiation.

Q.47 What is humus? Explain the role of earthworms in the formation of humus.


Humus is the decomposed plant and animal material which makes the soil fertile. Earthworms play a major role in converting large pieces of organic matter into rich humus, improving soil fertility.

Q.48 Why does the Earth’s average temperature remain relatively constant?


The atmosphere acts as a blanket and prevents the extreme fluctuation of temperatures, as air is a bad conductor of heat. The ‘greenhouse effect,’ which is caused by naturally occurring greenhouse gases like water vapour, keeps Earth’s surface temperature stable. This makes it possible for the planet to sustain life.

Q.49 What will be result if the CO2 concentration in the atmosphere increases? Give an example of what causes the concentration of carbon dioxide in the atmosphere to rise.


The temperature of the earth will increase due to global warming caused by greenhouse effect. The concentration of carbon dioxide in our atmosphere has increased as a result of human activity, intensifying the Earth’s natural greenhouse effect.

Q.50 With the help of a labelled diagram, show biogeochemical cycle through which nitrogen is converted into many forms


Q.51 With the help of a labelled diagram, show the cycling of carbon in nature.


Q.52 Suggest any two measures for avoiding misuse and wastage of potable water.


The two measures for avoiding misuse and wastage of potable water are as follows

1. Development of integrated water shed plan for drinking, irrigation, and industrial uses.
2. Transfer of surplus water to water deficit basins by interlinking rivers.

Q.53 (a) Name three processes through which oxygen is used from the atmosphere and one process through which oxygen is returned to the atmosphere.
(b) Mention three ways by which carbon returns to the C-cycle.


(a) Three processes by which oxygen is used from the atmosphere are:
1. Combustion
2. Respiration
3. Formation of oxides of nitrogen

The process by which oxygen is returned to the atmosphere is – photosynthesis.

(b) Three processes by which carbon is returned to the C-cycle are:
1. Both plants and animals release carbon dioxide to the atmosphere as a product of respiration.
2. By decomposition of organic wastes and dead bodies by decomposers.
3. By burning of fossil fuels like coal and petroleum.

Q.54 What is nitrogen fixation? Explain with the help of a diagram.


Nitrogen fixation is a biological process that converts nitrogen gas into a form that plants and other microorganisms can use. Nitrogen gas in the atmosphere is transformed into ammonia and other nitrogenous compounds in this process.

Q.55 (i) What are the abiotic components of the biosphere?
(ii) Identify A, B and C in the given image:


(i) The three abiotic components of the biosphere are: air, water and soil.

Q.56 Why are fishes not able to survive in a water body that supports dense algal growth?


Water body that supports dense algal growth is enriched with nutrients. The plant vegetation regularly consumes all the nutrients and oxygen at an increased rate from the water. As a result, other aquatic animals do not get oxygen for respiration and ultimately die. This process is called eutrophication. So, the possibility of survival of other living organisms is decreased in such water bodies.

Q.57 Complete the missing links in the oxygen cycle:


Q.58 Expand the term “CNG”. Why is it known as an eco-friendly fuel?


CNG stands for Compressed Natural Gas.

CNG is a substitute for fossils fuels like petrol, gasoline, diesel etc. It consists mainly of methane. It is a clear, odourless and non-corrosive fluid having a high calorific value. CNG is safer in case of leaks as it is lighter and spreads easily. It emits pollutants in considerably lesser amounts.

Q.59 Sulphur dioxide and nitrogen dioxide gases react with the water vapour present in air. What are the products formed by this reaction? What is this process known as and what are its effects?


Sulphur dioxide and nitrogen dioxide on reaction with water vapours form sulphuric acid and nitric acid respectively. This acid falls down along with the rain and this rain is called acid rain. It has harmful effects on plants, aquatic animals, and infrastructure. Aquatic life dies when water becomes acidic. This acid rain corrodes the metal and stones of buildings and monuments.

Q.60 Answer the following questions

(i) What distinguishes the atmosphere of the earth from that of other plants, such as Mars?
(ii) Mention two human activities that contribute to an increase in air pollutants.


(i) In planets such Mars, no life is known to exist, as CO2 constitutes up to 95 to 97% of the atmosphere whereas the earth’s atmosphere has only 0.03% of the CO2.

(ii) Human activities that lead to air pollution are:
– Industrialization and increasing vehicles have driven the increase of greenhouse gases in the atmosphere because of the use of low efficiency engines that throw products of incomplete combustion into the atmosphere.

– Deforestation due to increased urbanization has also lead to increased air pollution.

Q.61 Both UV-A and UV-B reach earth after passing through the ozone layer. However, as ozone layer is getting depleted, which of the two rays will be more harmful to earth and why?


UV-B is absorbed by the molecules of ozone, thus reducing UV-B exposure on the earth’s surface. But, on depletion of the ozone layer, UV-B radiation is allowed to pass through and its exposure at the earth’s surface increases. UV-B rays can directly damage the DNA, causing mutation that may lead to cancerous growth. It can damage collagen fibres which will accelerate aging of the skin and also destroy vitamin A in skin that may cause sunburn, tanning etc.

Q.62 Smog is a serious problem in many countries and continues to harm human health. Justify.


Smog is a visible indication of air pollution. It is a combination of various suspended particles with water vapour and dust. These suspended particles are unburnt carbon particles called hydrocarbons, produced due to combustion of fossil fuels. Ground-level ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide are harmful for senior citizens, children and people with heart and lung problems such as asthma. Smog hampers the visibility and harms the environment.

Q.63 Answer the following questions

(i) Apart from natural calamities like floods, human beings are also responsible for causing soil erosion. Discuss various activities of humans that lead to soil erosion.
(ii) Mention one biotic and abiotic factor that contributes in the formation of soil.


(i) Various human activities are:
– Ploughing of fields extensively, after harvesting over a period of time, makes the soil very loose and more prone to degradation.
– Tillage and cropping practices lower the soil organic matter levels, causing poor soil structure and increasing soil erodibility.
– Cattle and sheep that are left to graze their meadows trample the ground, particularly where they camp, leading to soil degradation.
– Fields are compacted by heavy machinery. Passage of heavy vehicles over the area destroy the vegetation and erode the soil.

(ii) Lichens (biotic factor) grow on the surface of the rocks and release some acidic substances that cause the rock surface to powder down and form a thin layer of soil.

Abiotic factor like water causes the widening of cracks in the rocks through their path of flow between them. Freezing of water inside the cracks further causes widening of the cracks. Flowing water wears away the hard rocks over a long period of time. Rocks rub against each other and get converted into smaller and smaller particles.

Q.64 Answer the following questions

(i) With help of a labelled diagram, show nitrogen cycle in nature.

(ii) Describe briefly any two processes involved in the cycling of nitrogen in the atmosphere.


(i) Nitrogen cycle:

(ii) Processes involved in the cycling of nitrogen in the atmosphere are:

– Fixing of nitrogen by nitrogen fixing bacteria that are found in the root nodules of the leguminous plants.

– Fixing of nitrogen by free living bacteria present in the soil that converts ammonia to nitrites and then to nitrates with the help of different bacteria. Other bacteria convert nitrates and nitrites into elemental nitrogen which goes back into the atmosphere.

Q.65 Answer the following questions

(i) How does the movement of air bring about changes in the atmosphere?
(ii) What are the various factors that influence winds?


(i) Changes in the atmosphere occur due to the heating of air and the formation of water vapours. Due to the heating of water bodies and the activities of living organisms, water vapour is formed. Radiations that are reflected back or re-radiated by the land or water bodies heat up the atmosphere. On being heated, convection currents are set-up in the atmosphere. Since the land gets heated faster than water, the air over the land also gets heated faster. Movement of air from one region to another creates winds and generates rainfall patterns that bring about changes in the atmosphere.

(ii) Various factors that influence winds are:

Rotation of the Earth

– Presence of mountain ranges in the path of the winds.

Q.66 Michael read about Green Houses built in colder regions to keep tropical plants warm. He explains how Earth’s atmosphere plays exactly similar role to keep the Earth warm, to his friend John. However, John raises his concern for Global Warming and concludes green house effect as main reason for global warming.

Answer the following questions, based on above information:
i. What is green house effect?
ii. Do you agree with John’s conclusion about green house effect?
iii. Why do you think, we need to reduce Global Warming? How can you contribute towards its reduction?


i. In colder regions, green houses are built. Glass of green house entraps heat and keeps the place warm for tropical plants. Earth’s atmosphere, entraps solar radiations and maintains the optimum heat, suitable for organism’s survival. This process is called greenhouse effect.
ii. Yes, in the atmosphere, green house effect is exhibited by green house gases (e.g. CO2, CH4 etc). Excess of accumulation of such gases, due to pollution, causes increased green house effect. Consequently, Earth’s temperature raises and leads to global warming.
iii. Higher temperature of earth causes melting of glaciers and ice on Polar regions, which lead to natural calamities like floods. As a result, global warming disturbs nature’s balance. Thus, it’s important to reduce it.
To reduce the global warming, we should:
(a) plant more trees.
(b) reduce the production of green house gases by using public transport or carpool, using alternative sources of energy.

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2. What is the list of chapters covered in Class 9 Science?

 The following list of chapters is covered in Class 9 Science:

  • Chapter 1 Matter in Our Surrounding

  • Chapter 2 Is Matter Around Us Pure
  • Chapter 3 Atoms and Molecules
  •  Chapter 4 Structure of the Atom
  •  Chapter 5 The Fundamental of Unit of Life
  •  Chapter 6 Tissues
  •  Chapter 7 Diversity in Living Organism
  •  Chapter 8 Motion
  •  Chapter 9 Force and Law of Motion
  •  Chapter 10 Gravitation