Important Questions for CBSE Class 9 Science Chapter 14 Natural Resources


Question.1 Name the three processes in which oxygen is used.
Answer. Combustion, respiration and in the formation of oxides of nitrogen.

Question.2 Name two natural resources available on the earth. [SAII -2014]
Answer. Water and air.

Question.3 Give one example of biotic component of the biosphere.
Answer. All animals, plants and microorganisms.

Question.4 Identify which of the following are not the part of biotic environment, soil, plants, fish, air, insects.
Answer. Soil, air.

Question.5 Name two oxides formed by burning of fossil fuels, which are responsible for acid rain.  [SAII – 2013]
Answer. The oxides of nitrogen and sulphur:
(i) Sulphur dioxide and sulphur trioxide.
(ii) Nitrous oxide and nitrogen dioxide.

Question.6 Mention the two forms of precipitation in nature when the temperature of air is very low.
Answer. (i) Fog and smog, (ii) Hail, (iii) Mist, (any two)

Question.7 Name the factor responsible for change in rainfall patterns in India. [SAII – 2012]
Answer. Rainfall patterns are decided by the prevailing wind patterns. In large part of India, rains are mostly brought by South-West or North-East monsoons.

Question.8 Combustion of fossil fuels results in the increase of suspended particles in the air. What are these particles ?
Answer. The suspended particles in the air could be unburnt carbon particles or hydrocarbons which lead to smog.

Question.9 How the frozen water between cracked rocks causes the cracks to widen ? [SAII – 2014]
Answer. The water inside the cracked rocks expand on freezing. When it expands, its volume increases and it causes the cracks to widen.

Question.10 Name two gases which cause greenhouse effect.
Answer. (i) Carbon dioxide, (ii) Methane, (iii) Oxides of nitrogen, (any two)

Question.11 Name two biologically important compounds that contain both oxygen and nitrogen.
Answer. Proteins and nucleic acids (DNA and RNA).

Question.12 Name two essential biological molecules in which oxygen is present.
Answer. (a) Proteins, (b) Carbohydrates, (c)‘ Fats aid lipids, (d) Nucleic acids, (any two)

Question.13 Name two biologically important compounds that contain both oxygen and nitrogen.  [SAII-2011]
Answer. Proteins and nucleic acids (DNA and RNA).

Question.14 What is the greenhouse effect ? [SAII – 2011]
Answer. Some gases prevent the escape of heat from the Earth. An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase worldwide and this is called the greenhouse effect.

Question.1 The atmosphere acts as a blanket, how ? [SAII – 2012]
Answer. Air is a bad conductor of heat which keeps average temperature of the Earth steady during day and  at night. The ozone shield of the atmosphere absorbs most of the harmful radiations coming from Sun.

Question.2 Name four human activities which cause air pollution. [SAII – 2013]
(a) Mining activities : Dust released due to mining activities.
(b) Thermal power plants : Fossil fuel burnt in these places causes air pollution.
(c) Firework on festivals : It results in the release of toxic chemicals into air along with hot and toxic gases.
(d) Burning of fossil fuel : In industries, automobiles, domestic purposes etc.

Question.3 Name the stages of the life cycle of aquatic animals which are affected by change in temperature.
Answer. The eggs and larvae of various aquatic animals are susceptible to temperature changes. As the aquatic organisms are used to a certain range of temperature in the water body where they live, and sudden marked change in this temperature would be dangerous for them or affect their breeding.

Question.4 How do sun and wind influence the formation of soil ? [SAII -2014]
Answer. The Sun: The Sun heats up rocks during the day so they expand and at night they cool down and contract. This results in the formation of cracks and rocks ultimately break up into smaller pieces. Wind : Strong winds help in the formation of rock particles by their erosional actions. This helps in formation of soil,

Question.5 Define weathering. Write the different means which cause weathering. [SAII -2014]
Answer. The process of breaking down of rocks into small, fine mineral particles is called weathering.

  •  The weathering may occur due to physical, chemical or biological means.

Question.6 Write the composition of soil. On what basis is the type of soil decided ? [SAII – 2013]
Answer. Soil is a mixture. It is composed of small particles of rocks of different sizes, humus (bits of decaying living organism) and various micro-organisms.

  •  The type of soil is decided by the average size of particles found in it.

Question.7 What are the consequences of global warming ? [SAII -2012]

  • An increase in temperature of earth even by 1 °C may lead to melting of ice on the poles.
  •  The melting of ice will result in rise of sea level.
  •  Due to rise in sea level,many coastal cities will be flooded or submerged.
  •  Increase in temperature of earth, results the changes in weather and may cause excessive raining or drought or extreme hot or cold weather conditions.

Question.8 How are clouds formed ?  [SAII – 2013]
Answer. The water evaporates due to heating Up of water bodies and other biological activities. The air also heats and rises. On rising, it expands and cools to form tiny droplets. These droplets grow bigger, expand and form clouds. The collection of dust and other suspended particles facilitate the process.

Question.9 What is the major source of freshwater in the city/town/village where you live ? [SAII -2011]
Answer. The major sources, of freshwater in the city/town/village is the underground water which is mostly taken out with the help of hand pumps or tube wells. The rivers flowing in the nearby areas, lakes and ponds also serve as the source of freshwater.

Question.10 What is soil erosion ? [SAII -2012]
Answer. The removal of topsoil which is rich in humus and nutrients by flowing water or wind is known as soil erosion. If this process continues further, then all soil may get washed away and the rocks underneath may get exposed. It may lead to the loss of all valuable resources because nothing grows as such on the rocks.

Question.11 What are the two forms of oxygen found in the atmosphere ? [SAII -2011]
(i) Elemental oxygen is normally found in the form of a diatomic molecule (O2) in the lower regions of the atmosphere to the extent of 21%. It is non-poisonous form of oxygen.
(ii) But in the upper reaches of the atmosphere (stratosphere), it occurs in the form of ozone, containing three atoms of oxygen and having the molecular formula O3. It is the poisonous form of oxygen

Question.1 Name the various organisms involved in nitrogen cycle. [SAII -2014]

  1.  Nitrogen fixing bacteria, e.g., Rhizobium, Azotobacter.
  2.  Bacteria which convert complex nitrogenous organic compounds (proteins) into ammonia, e.g., Actinomyces.
  3.  Nitrifying bacteria which converts ammonia into nitrates, e.g., Nitrosomonas and nitrobactor.
  4. Denitrifying bacteria, e.g., Pseudomonas.

Question.2 What are the three ways by  which CO2 is returned back into atmosphere ? [SAII -2011]
Answer. The three ways by which CO2 is returned back into atmosphere are :

  1.  By the decomposition of dead organic matter.
  2.  As the product of respiration by both plants and animals.
  3.  As the gaseous waste formed by the combustion of fuels like coal, wood, petrol and gaseous fuels.

Question.3 Define biosphere. Name its components. [SAII -2012]
(a) The life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible is known as biosphere.
(b) Two components of biosphere ate :
(i) Biotic : All living forms such as:plants, animals .and microorganisms.
(ii) Abiotic : Air, water and the soil.

Question.4 Mention three ways by which atmosphere regulates the average temperature on Earth.
(a) As the air is a bad conductor  of  heat, therefore, the atmosphere keeps the average temperature pf the earth fairly steady during the day even during  the course of the whole year.
(b) The atmosphere prevents the  sudden increase in hours.
(c) During the night, it slows down the escape of heat into the outer space and prevents the earth from excessive cooling.

(a) Explain the formation of acid rain.
(b) What does the presence of smog in an area indicate ? [SAII – 2014]
Answer. (a)

  •  Acid rain is the rainwater which contains excessive amount of acids/.e., sulphuric acid and nitric acid.
  •  These acids are formed in the atmosphere by the reaction of oxides of sulphur and
    nitrogen with water.
  • The Oxides of sulphur and nitrogen are produced by combustion of fossil fuels in industries, automobiles, thermal power plants and domestic appliances etc.
  •  The sulphur and nitrogen, present in fossil fuels form these oxides by reacting with oxygen of air by the process of combustion.

(b) The presence of smog in an area indicates the high percentage of smoke released in the air by combustion of fossil fuel in industries, thermal power plants or automobiles. It is an indicator of air pollution.

Question.6 What are the harmful effects of air pollution ? [SAII – 2012]

  1. It may cause respiratory problems like sneezing, allergy, asthma or bronchitis in some persons.
  2. It may cause acid rain which leads to deterioration of metals and other building material.
  3. It may cause global warming which leads to change in the climate of the Earth.
  4. Carbon monoxide may lead to many problems of respiratory system.
  5. Smog, which reduces the visibility as well as causes respiratory ailments.

Question.7 Mention any three important roles of water required for organisms on the earth’s surface.

  1.  All cellular processes take place in water medium.
  2.  Water regulates-body temperature.
  3. Water is required for transportation of nutrients from one part of the body to the other.

(a) Explain how soil pollution is caused ?
(b) Write three ways to prevent soil pollution. [SAII -2014]
(a) The soil pollution may be caused by dumping the industrial wastes in vacant sites viz., along the roads, railways tracks or sanitary land fields etc. The wastes from residences, cattle sheds, industries, agricultural fields etc. also pollute the soil. The excessive use of fertilizers and pesticides also pollutes the soil.

  1.  By judicious use of fertilizers and pesticides.
  2. By proper management of disposal of household waste.
  3. Intensive cropping, terrace farming should be practiced.

Question.9 Explain the following terms:
(i) Nitrogen fixation, (ii) Nitrification, (iii) Denitrification. [SAII – 2013]

  1. The process in which atmospheric nitrogen is converted into usable forms like ammonia, nitrates, nitrites or N02 etc. is called nitrogen fixation.
  2. The process of formation of nitrites and then to nitrates from ammonium compounds is called nitrification.
  3. The process of conversion of some ammonium compounds, nitrites and nitrates into molecular nitrogen is called denitrification.

(a)ozone layer found ?
(b)What is ozone hole and how is it caused ? Where is
(c)State the harmful effects of ozone depletion. [SAII -2014]
(a)Ozone layer is found in stratosphere about 18-50 km above the atmosphere.
(b)Thinning of ozone layer over a restricted area is called ozone hole.
The excessive use of chemical substances like CFCs is the major cause for depletion of ozone layer. These chemicals reach the stratosphere and start reacting with ozone layer and results in thinning of ozone layer over a restricted area.
(c) The depletion of ozone layer may cause :
(i) Skin cancer
(ii) Damage to eyes
(iii) Damage to immune system
(iv) In plants also it may increase the harmful mutations.

Question.11 What causes winds ? [SAII – 2012, 13]
Answer. Winds are caused due to unequal heating of atmospheric air. This phenomena can easily be seen near coastal regions during the daytime. 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.

Question.12 List any three human activities that you think would lead to air pollution. ]SAII – 2013]
Answer. Human activities that would lead to air pollution are :

  1. Excessive use and burning of fossil fuels like coal and petroleum produces different oxides of nitnopfrand sulphur. These are not only dangerous to our respiratory system but also leads to acid rain.
  2. Incomplete combustion of various fuels forms unburnt carbon particles which lowers the visibility, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.
  3. Large usage of automobiles and improperly tuning of engines leads to the formation of carbon monoxide gas and other oxides of nitrogen which causes lot of respiratory problems.
  4. Forest fires, excessive mining and ore refining, excessive use of chlorofluorocarbons and v excessive industrialization leads to air pollution.

Question.13 Why do organisms need water ? [SAII-2012]
Answer. Organisms need water due to the following reasons :

  1. All cellular processes take place in a water medium.
  2. All the reactions that take place’Within our body and within the cells occur between substances that are dissolved in water.
  3. Substances are also transported from one part of the body to the other in a dissolved form.
  4. Water makes-up about 70% of body weight of all living organisms.
  5. It helps in the digestion of food and absorption of nutrients in the blood. Hence, organisms need to maintain the level of water within their bodies in order to stay alive.
  6. It helps in maintaining body temperature. –

Question.14 Do you know any activity which may be polluting these water sources ?
Answer.There are many activities which cause pollution of water sources such as :

  1. Dumping of waste from factories, sewage from our towns and cities into rivers or lakes.
  2.  Discharging hot water from cooling towers into the water bodies affects the breeding capacity of aquatic organisms.

Question.15 How is soil formed ? [SAII – 2013, 2014]
Answer. Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes. The end product of this breaking down is the fine particles of soil. There are many other factors which play a vital role in the formation of soil. These factors are :

  1. The Sun : It causes heating of rocks which causes cracking and ultimately breaking-up into smaller pieces.
  2. Water : It breaks rocks both by freezing and fast flow.
  3. Wind : It causes erosion of rocks similar to as done by fast flowing water. It also carries sand from one place to the other like water does.
  4. Living organisms : Lichens and moss plants grow on the rock surface and cause rock surface to powder down and form a thin layer of soil. The roots of big trees sometimes go into cracks in the rocks and as the roots grow bigger, the crack is forced bigger.

Question.16 What are the different states in which water is found during the water cycle ? [SAII – 2011]
Answer. Three different states of water can be seen during the water cycle. These states are :

  1. Gaseous stateTtn the form of water vapour which evaporates from the surface water).
  2. Liquid state (It is formed by the condensation of water vapour and can be seen in the form of rain).
    (iii) Solid state (It is formed by the freezing of liquid droplets in the upper layer of atmosphere which can be seen in the form of snow, hail or sleet).

Question.17 List any three human activities which would lead to an increase in the carbon dioxide content of air. [SAII – 2011]
Answer.Three human activities which would lead to an increase in the CO2  content of air are :

  1. Respiration : It is the natural process of release of CO2   by both plants and animals. But this release is neither dangerous nor it has any adverse effect on our environment.
  2. Combustion of fuels : The various types of fuels are burnt to provide energy for various – , needs like heating, cooking, transportation and industrial fuels.
  3. Deforestation : Trees help in the conversion of CO2   into organic compounds such as glucose, starch etc., by the process of photosynthesis. When these trees are cut non- judiciously, then the level CO2   increases in our environment.

Question.18 How are living organisms dependent on the soil ? Are organisms that live in water totally independent of soil as a resource ? [SAII – 2014]
Answer. Living organisms are dependent on the soil in the following ways :

  1.  Soil provides a natural habitat for various different organisms (such as bacteria, fungi, algae) which help in improving the quality of the soil. Thus, they maintain the fertility of the soil.
  2. Number of insects, animals like rats, rabbits etc. build their home in the soil.
  3.  Earthworms perform all their activities in the soil. They maintain fertility also as their excreta is rich in nitrogen.
  4.  Soil pro/ides anchorage and nutrients to the plants for their growth and development.

Yes, all organisms that live in water are totally dependent on soil as a resource : The mineral, nytrients are present in water in the dissolved form. But their recycling takes place only with the help of decomposers which are present in the soil beds. Thus, all water bodies has soil beds which contain decomposers for the recycling of nutrients and to convert them into readily absorbable forms.

Question.19 You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather ?
Answer. Weather observatories collect information regarding the pattern of temperature, speed of wind, air pressure, ocean features and all other features which can affect the weather. This information is collected by remote sensing and weather forecasting satellites. The information collected is then sent to the meteorological departments which prepare a weather report which is displayed on the maps. This information is further transmitted through radio and television.
You might have heard about weather report saying ‘depressions’ in the Bay of Bengal have caused rains in some areas.

Question.20 We know that many human activities lead to increasing levels of pollution of the air, water bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution ? [SAII -2012]
Answer. Yes, definitely if these activities are isolated to specific and limited areas, then the level of pollution of the air, water bodies and soil will decrease. For example :
(i) If all the sewage discharge, industrial waste is collected and treated properly before discharging into water bodies, then obviously aquatic life in these water bodies will be  affected to a little extent.
(ii) If hot water from the industries (which is used for cooling machines and other devices) is collected at a commonplace and cooled and aerated properly before discharging into water bodies. Then this will not affect the breeding capacity of aquatic organisms.
(iii) If all the industries and commercial places of a city/town are located in a particular area which is far away from a residential area. Then all diseases resulting from air pollution could be minimised.
(iv) Above all, if we use only biodegradable substances, then they will get decomposed easily and there will be very little pollution of our precious natural resources.

Question.1 What are the various causes of soil erosion. [SAII – 2014]
Answer. Causes of Soil Erosion :
(i) Wind causes soil erosion by”carrying away the topsoil particles.
(ii) Rain causes soil erosion on unprotected topsoil by washing it down.
(iii)Improper farming or tilling and leaving the field fallow for long time causes soil erosion.
(iv)Frequent flooding of rivers causes soil erosion by removing the topsoil of the fields near the river banks.
(v) Deforestation also leads to soil erosion.

Question.2 Explain the role of the sun in the formation of soil. Justify “Dust is a pollutant” [SAII -2012]

  •  Sun plays an important role in the formation of soil.
  •  The rocks heat up and expand under the influence of solar radiations.
  •  At night the rocks cool down and contract.
  •  Continuous expansion and contraction and uneven heating of different parts of rocks
    tends to break them into smaller pieces. .
  •  These smaller pieces of rocks play an important role in the formation of soil.


  •  Dust causes many respiratory problems like asthma, lung cancer, bronchitis etc.
  •  Dust along with smoke and water vapour forms smog. It causes respiratory problems in humans and reduces visibility leading to accidents.
  •  Inhalation of dust of cement, asbestos or coal etc. may cause sneezing and allergy or TB.

Question.3 How does nitrogen fixation take place during lightning ? How do plants make use of the nitrates and nitrites present in soil ? [SAII -2014]
Nitrogen fixing bacteria mostly found in the root nodules of leguminous plants convert
atmospheric nitrogen molecules into nitrates.
During lightning, the high temperatures and pressure created in the air convert nitrogen into
oxides of nitrogen. These oxides dissolve in water to give nitrous and nitric acids that fall on
land along with rain.

  •  Nitrogen fixing bacteria which are found in the roots of leguminous plants convert atmospheric nitrogen into  nitrate (the usable form by plants).
  •  During lightning and thunder, the high temperature and pressure help to convert atmospheric nitrogen into  oxides of nitrogen and to give nitric and nitrous acids which fall along with rain.
  •  The plants use nitrogen in the form of nitrates and nitrites to form amino acids and
  •  The plants are used as food by animals.
  •  After the death of plants and animals, the bacteria convert these compounds of nitrogen into nitrates and  nitrites, which are used by new plants to grow.
  •  Some other types of bacteria convert nitrites and nitrates into molecular nitrogen, which escapes into  atmosphere and becomes a part of it.

Question.4 Draw labelled diagrams of :
(a) Carbon cycle
(b) Oxygen cycle and briefly explain oxygen cycle.[SAII – 2013]
Answer. (a)
Oxygen cycle:

  •  Oxygen from the atmosphere is used up in combustion, respiration and
    in the formation, of oxides of nitrogen.
  •  Oxygen is returned to the atmosphere through photosynthesis. This
    constitutes oxygen cycle in nature.

Question.5 What are the methods of preventing or reducing soil erosion ? [SAII -2012]
Answer. The methods of preventing soil erosion are :
(i) Afforestation : Forests reduce erosion as the roots of trees hold the soil in place.
(ii) Shelter belts : Trees planted in lines or hedges around farmland reduce erosion by
reducing the speed of the wind.
(iii) Contour ploughing : Farmers plough land so that furrows lie across the natural slope of
the land. These furrows trap water and do not allow it to flow down carrying the topsoil.
(iv) Terrace (or step) farming : A terraced hillside is less likely to tie eroded than a natural
hillside. Here a series of steps formed by horizontal strips supported by walls, catch the
descending water. It gives the water sufficient time to percolate Into the soil and nourish
the crop.
(v) Soil cover : Soil left bare after harvesting a crop is often covered with dried vegetation to prevent erosion. Steep slopes that cannot be ploughed are covered with grass or pasture crops.
(vi) Preventing overgrazing : As the grass has a tendency to bind soil molecules, so even a very little grass on a field prevents erosion of soil. But if the grass is overgrazed, it exposes the soil to erosion.

Question.6 Why is the atmosphere essential for life ? [SAII-2011]
Answer. Atmosphere is essential for life because of the following reasons :
(i) It keeps the average temperature of the earth fairly steady during the day and even during the course of the whole year.
(ii) It prevents the sudden increase in temperature during the daylight hours.
(iii) It contains all the important gases which are required for sustaining life on earth. These gases are :
(a) Oxygen for respiration of living organisms and oxidation.
(b) Carbon dioxide for photosynthesis in plants and for making food.
(c) Nitrogen foTproviding inert atmosphere and making proteins.
(iv) The stratosphere region (16-23 km from the surface of Earth) of atmosphere contains a thick layer of ozone which filters the harmful UV radiation from Sun. If these radiations reach on the surface of Earth, then they may cause cancer in animals and are also harmful for plants.

Question.7 Write a note on how forests influence the quality of our air, soil and water resources.
[SAII – 2014]
Answer. Forests influence the quality of air, soil and water resources in the following ways :
(i) Influence of forests in controlling the quality of air :
(а) Forests help in minimising the level of CO2 in the atmosphere. This prevents – , greenhouse effect and global warming.
(b) Forests reduce environmental temperature which in turn increases the rate of photosynthesis in plants in the surrounding regions.
(c) Some of the trees have the abllity to absorb harmful gases present in the atmosphere, e.g., Jamun trees can absorb compounds of lead easily.
(ii) Influence of forests in controlling the quality of soil:
(a) The roots of huge trees spread in a larger area and prevent erosion of topsoil by holding the soil particles tightly.
(b) Forests also regulate biogeochemical cycles which are responsible for cycling of nutrients and making them available for the plants in the soil.
(c) Many of the decomposing bacteria and nitrogen-fixing bacteria live in close association with the roots of the trees.
(iii) Influence of forests in controlling the quality of water :
(a) Forests help in returning pure water back to the surface of earth through rains.
(b) Forests help in maintaining the water cycle as well as water resources of the earth.


Question.1 There is mass mortality of fishes in a pond. What may be the reasons ? [SAII -2013]

  1. Thermal pollution.
  2. Addition of poisonous (mercury) compounds in water.
  3. Due to blockage of gills with any pollutant.

Question.2 Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil ?
Answer. Lichens release chemical substances to break the rocks into smaller particles and hence make soil.

Question.3 “Soil is formed by water.” If you agree to this statement then give reasons.
Answer. Water helps in the formation of soil in the following ways :

  1.  Water causes ‘wear off’ of rocks over a long period of time.
  2. It also causes the rocks to rub against other rocks creating small particles which are taken away downstream and deposited as soil.
  3. Water expands on freezing in crevices of rocks and crack rocks into smaller pieces.

Question.4 Justify “Dust is a pollutant”. [SAII – 2014]
Answer. Dust remains present in air as suspended particles can cause allergy and other respiratory diseases. It also affects plant growth by covering stomata on leaf surface. It acts as the carrier of toxic compounds like heavy metals.

Question.5 Explain the role of the Sun in the formation of soil. ..
Answer. The rocks are heated by the sun; they contract during night but not at same rate – resulting in cracks in rocks and ultimately to smaller particles.

Question.6 What are the various forms in which oxygen is available ? [SAII -2011]

  1. In the atmosphere, oxygen is found in the elemental form to the extent of 21 %.
  2. In combined form, it occurs as CO2 both in the earth’s crust as well as in the air.
  3. In the crust, it is found as the oxides of most metals and silicon and also as carbonate,  sulphate, nitrate and other minerals.
  4. It is also an essential component of most biological molecules like carbohydrates, proteins, nucleic acids and fats (or lipids).

Question.7 What causes movement of air ? Mention’the factors which influence these winds ? [SAII – 2012]

  1. Uneven heating of the atmosphere.
  2. Rotation of the earth.
  3. Presence of mountain range.
  4. Difference in cooling and heating of land and water bodies.
  5. Formation and condensation of water vapours, (any two)

Question.8 Explain why is there a change in the wind direction in coastal areas during the day and at night. [SAII -2012]
Answer. During the day: Air above the land gets heated faster and starts rising to create a region of low pressure. While the sea water does not get heated so rapidly and the air above it remains cool. This causes the air over the sea to move into the region of low pressure i.e., towards land. During the night : At night, the land and sea starts cooling. The land cools faster than the water, so the air above water is warmer than the air above land and hence, the direction of wind is reversed i.e., from land to the sea.

Question.9 How is the atmosphere of Venus/Mars different from that of the Earth ? Name two main gases present in earth’s atmosphere. [SAII -2013]

  •  The major component of the atmosphere of Venus/Mars is carbon dioxide while on Earth it is only a fraction of a per cent.
  •  The carbon dioxide constitutes upto 95-97% of the atmosphere on Venus and Mars but it constitutes only 0.03 to 0.04% of atmosphere on Earth.
  •  Two main gases present in Earth’s atmosphere are nitrogen and oxygen.

Question.10 In what forms the water is found on the earth surface ? Describe in brief. [SAII -2011]

  •  Most of the water on Earth’s surface is found in the form of liquid in seas, oceans, rivers, lakes, ponds etc.
  •  It is found in the form of ice (solid) in the ice-caps on mountain peaks and in polar regions.
  •  Water is also found in vapour state when it evaporates at the surface of water bodies, as moisture in the atmosphere, air transpired by plants and air exhaled by animals.

Question.11 ‘A change in temperature in the water body affects aquatic organisms’. Explain in brief.
[SAII -2013]
Answer.Change in the water temperature can affect the aquatic life in the following ways :

  1.  It can encourage the growth of some life forms and harm some other life forms.
  2. This affects the balance between various organisms which had been established in that – system.
  3. This can lead to removal of desirable substances like oxygen and other nutrients from water
  4. The eggs and larvae of various animals are particularly susceptible to temperature changes.
    So such aquatic life forms may become extinct from the related water bodies.
  5. The breeding of aquatic organisms will be affected.

(a) In what ways the water cycle helps the marine organisms ?
(b) ‘The biosphere is a dynamic but stable system.’ Justify this statement. [SAII – 2013]

  •  Water is capable of dissolving a large number of substances.
  •  Water flows through or over rocks containing soluble minerals.
  •  Some of the minerals get dissolved in the water which is carried by water bodies and made available to aquatic organisms.


  •  There is a constant interaction between the biotic and abiotic components of the
  •  These interactions consist of a transfer of matter and energy between the different components of the biosphere and make it a dynamic but stable system.

Question.13 Describe how lichens and big trees influence the formation of soil.

  1. Lichens grow on the surface of rocks and release substances that powder down the rock surface.
  2.  Moss grows on this surface and breaks it further.
  3. The roots of trees grow into rocks, form cracks and widen them further to form soil.

Question.14 How is soil formed ? List four factors which play a vital role in the formation of soil.  [SAII – 2014]
Soil is formed by breakdown of rocks by various physical, biological and chemical processes. Following factors play important role in the formation of soil :
(i) Temperature variations due to solar radiation, (ii) Rainwater, (iii) Wind, (iv) Living organisms.

(а) Explain how forests influence the quality of our air, soil and water resources.
(b) State two ways in which atmospheric carbon dioxide is fixed. [SAII -2014]
(a) Forests influence the quality of our air, soil and water resources in many ways :

  • The vegetation/trees in the forest purify the air by the process of photosynthesis.
  • The roots of trees and plants, bind the soil and prevent the soil erosion as well as floods.
  •  The roots absorb the water present in the soil as groundwater.
  •  The water released by the process of transpiration as water vapour becomes a part of
    atmosphere which helps to bring the rain.
  •  The forests also help to regulate the temperature of air.

(b)  (i) Carbon dioxide is fixed into carbohydrate by the process of photosynthesis.
(ii) The carbon dioxide is fixed in the form of carbonates and bicarbonates; compounds and endoskeletons  and exoskeletons of various animals are formed from carbonate salts.

Question.16 Carbon dioxide is necessary for plants, justify this statement. Why do we consider it as a pollutant ?
Answer.It is true that carbon dioxide is necessary for plants as it is used in photosynthesis.
In photosynthesis, carbon dioxide is fixed into carbohydrate.
Question.16 Carbohydrate is the major source of food for all heterotrophs.
Excess quantity of carbon dioxide results in greenhouse effect and leads to global warming. The excess carbon dioxide in air may cause several respiratory problems in living beings. Therefore, the carbon dioxide, if produced in excess quantity is considered as a pollutant.

(а) Write the name of triatomic molecule of oxygen.
(b) Is its presence necessary in nature ?
(c) How does it affect the environment ? Explain. [SAII – 2013]
(a) The triatomic form of oxygen is called ozone.
(b) Yes, its presence is necessary in nature.
(c) Ozone absorbs the harmful radiations from the Sun and, thereby protects many forms of life from getting damaged.

Higher Order Thinking Skills (HOTS) Question

Question.1 Rivers from land, add minerals to sea water. Discuss how. [SAII – 2013]
Answer.Water is capable of dissolving a large number of substances. As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. Thus, rivers carry many nutrients from land to the sea.

Question.2 How can we prevent the loss of topsoil ?
Answer.Loss of topsoil can be prevented by :

  1. increasing the vegetational cover
  2. checking the falling of trees
  3. by preventing excessive grazing by animals.

Question.3 Fertile soil has lots of humus. Why ? [SAII-2012]
Answer. Fertile soils are rich in organisms that decompose dead organic matter forming humus. Humus gives minerals, absorbs water and makes soil porous.

Question.4 Following are a few organisms :
(a) lichen (b) mosses
(c) mango tree (d) cactus
Which among the above can grow on stones and also help in formation of soil ? Write the mode of their action for making soil. [SAII – 2014]
Answer. Lichens and mosses (a) and (b). Lichens and mosses release substances which break down the stones resulting in the formation of soil.

Question.5 Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic.  
Answer. Abiotic factors making soil — sun, water, wind. Biotic factors — lichens, mosses and trees.

Question.6 A motor car, with its glass totally closed, is parked directly under the sun. The inside temperature of the car rises very high. Explain why.
Answer. Infrared radiations in sunlight pass through the glass and heat the interior of the car. The radiation emitted by upholstery and other inner parts of the car cannot pass out of the glass, so the heat trapped inside raises the temperature of the interior. This is because glass is transparent to infrared radiation from the sun having smaller wavelength than that emitted by the interior of the car which are of longer wavelength to which the glass is opaque.

Question.7 What is the importance of carbon cycle ? [SAII – 2014]
Answer. It helps to maintain a constant level of CO2 in the earth’s atmosphere which further help in maintaining earth’s temperature through greenhouse effect.

Question.8 What is meant by the following terms :
(i) Soil (ii) Pedogenesis? [SAII – 2012]
(i) Soil: It is the humus containing and life sustaining weathered uppermost crust of earth.
(ii) Pedogenesis : The process of formation of soil is called pedogenesis.

Question.9 Give two examples where oxygen is not playing any role in supporting life.

  1. Some bacteria are poisoned by elemental oxygen.
  2. The process of nitrogen-fixing by bacteria does not take place in the presence of oxygen.

Question.10 Name any two kinds of fertilizers whose excessive presence in water bodies result in algal
growth. What is the consequence of eutrophication ? Define eutrophication.

  1. Nitrates and phosphates.
  2. The presence of nitrates arid phosphate fertilizers in sewage water provide a lot of nutrients to the algae present in the water body and causes algal bloom. When the algae die, the aerobic decomposers become active and consume all the dissolved oxygen of water. This results in shortage of oxygen for other aquatic life forms, ultimately resulting in their death.
  3. Eutrophication : The process in which the presence of extra quantity of nitrogenous and phosphate fertilizers leads to excessive growth of algae in the water body which further leads to depletion of dissolved oxygen in water, resulting in killing of other aquatic organisms.

Reasoning Questions

Question.1 Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere ? [SAII – 2013]
Answer. Cycling of these gases maintains consistency.

Question.2 Why does moon have very cold and very hot temperature variations, e.g., from -190 °C to 110 °C even though it is at the same distance from the sun as the earth is ?
Answer. Absence of atmosphere on the moon.

Question.3 Why does Mathura refinery pose problems to the Taj Mahal ? [SAII – 2014]
Answer. Mathura refinery releases toxic gases (like oxides of sulphur) which causes acid rain and hence corrosion of the marbles of Taj Mahal.

Question.4 Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling ?
Answer. It is a bio-indicator and sensitive to SO2pollution from automobiles. Delhi has maximum number of automobiles, hence has a highly polluted environment.

Question.5 Why doeswater need conservation even though large oceans surround the land masses ?
Answer. Marine water is not useful for human and plant life directly. Uneven distribution of limited freshwater resources need conservation to cater to the demands.

Question.6 State reasons for the following:
(i) Excess burning of coal causes greenhouse effect.
(ii) Soil isamixtui
(iii) Temperature ranges from -190 °C to 110 °C on the surface of the moon.

  • Excess burning of coal produces greenhouse gases like carbon dioxide and hydrocarbons.
  •  These gases have a tendency to trap the heat of the sun, thereby causing greenhouse effect.

(ii) Soil is a mixture as it contains small particles of rock (of different sizes), bits of decayed . living organisms and various forms of microscopic life. It also contains air and water
(moisture) in it.
(iii) The moon has no atmosphere. The atmosphere helps to regulate the temperature. In absence of atmosphere, the temperature on the surface of moon ranges from -190 °C to 110 °C.

Question.7 Explain why are root nodules useful for the plants ? [SAII-2012]
Answer. Root nodules contain the symbiotic bacteria, Rhizobium which convert/fix the atmospheric nitrogen into usable form /.e., nitrates’Which are utilised by plants for the synthesis of amino acids and proteins.

Important Topics/Areas/Questions which are
frequently asked in the examination

(a) What is the outermost layer of our Earth called ?
(b) How is this important to life forms ? ‘
(c) Name four factors that help in the formation of soil from rocks.
(a) The outermost layer of our Earth is called crust. The outer crust of Earth is called lithosphere.
(b) The living forms get all substances of their requirement for supporting life form this region.
(c) (i) Winds, (ii) Water, (iii) Living organisms, (iv) Temperature variations (due to solar radiation).

Question.2 Write in brief the harmful effects of water pollution. [SAII – 2014]

  •  Causes water borne disease.
  • Destroys microorganisms thereby affecting self purification of water.
  •  Decreases amount of dissolved 02 in water bodies.
  •  Changes the temperature of water, oceans, leading to melting of polar ice.
  • Disturbs aquatic life.
  • Kills aquatic organisms.

Question.3 Mention any three human activities which are responsible for water pollution. [SAII -2013]

  1.  Excessive use of fertilizers and pesticides.
  2. Disposal of industrial waste which contains poisonous substances into nearby water bodies.
  3. Sewage discharged into sewers from household/domestic units.
  4. Synthetic soap and detergents used during washing in household units.
  5.  Hot water released from industrial units.

Question.4 What are the harmful effects of modern farming practices ? Mention any three effects:
[SAII- 2013, 14]

  1.  Modern farming practices are based on excessive use of fertilizers and pesticides.
  2. These are used to increase the crop production as well as for pest and weed control.
  3. From the soil, these chemicals enter the food chain and affect the life of living organisms.

The harmful effects are :

  1. The excessive use of fertilizers and pesticides affects the fertility of soil and changes its texture i.e., it may become acidic or alkaline and less fertile.
  2. Harmful non-biodegradable chemicals enter the food chain and adversely affect the health of animals or even human.
  3. Excessive use of fertilizers and pesticides in the long run reduces the crop yield or soil.fertility and kills the diversity of organisms that live in it.

Question.5 What is the chemical formula of ozone ? What essential function does this gas perform and where it is found ? What are CFCs ? [SAII – 2014]

  1. Ozone (O3).
  2. It absorbs the harmful solar UV radiation to prevent various harmful effects on man, animals and plants.
  3. Ozone is found in the stratosphere, i.e., about 18-50 km above the atmosphere.
  4. CFCs (Chlorofluorocarbons) are synthetic harmful chemicals which are used in refrigerators and air conditioners as coolants, in fire extinguishers, in aerosol sprayers etc. They are responsible for depletion of ozone layer in the atmosphere.

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