NCERT Exemplar Solutions Class 9 Science Natural Resources

Multiple Choice Questions (MCQs)............................

Question 1:  The atmosphere of the earth is heated by radiations which are mainly

(a) Radiated by the sun                             

(b) Re-radiated by land

(c) Re-radiated by water                           

(d) Re-radiated by land and water

Solution 1:   (d) Re-radiated by land and water. 

Some solar radiation is absorbed by the soil, but the vast majority is reflected back or re-radiated by land and water bodies. The atmosphere is heated by re-radiated or reflected solar radiation. Convection currents result as a result of this.

Question 2: If there were no atmosphere around the earth, the temperature of the earth will
(a) increase
(b) go on decreasing
(c) increase during day and decrease during night
(d) be unaffected

Solution 2:  (c) increase during day and decrease during night. 

Air is a limitless natural resource. There would be no life, no winds, clouds, or rain, no fires, and no protection from harmful solar radiation if there was no air. This is due to the atmosphere's blanket-like coverage of the earth. As air is a poor conductor of heat the atmosphere keeps the average temperature of the earth reasonably steady during the day and even during the course of whole year.
Only abrupt temperature increases during daylight hours are prevented by the atmosphere. The atmosphere often slows the release of heat into space at night. For example, the moon is around the same distance from the sun as the earth, but it lacks an atmosphere similar to ours. The temperature of the moon varies from -190° C to 110° C due to the lack of an atmosphere.

Question 3:  What would happen, if all the oxygen present in the environment is converted to ozone?
(a) We will be protected more
(b) It will become poisonous and kill living forms
(c) Ozone is not stable, hence it will be toxic
(d) It will help harmful sun radiations to reach earth and damage many life forms

Solution 3:  (b) It will become poisonous and kill living forms. 

Ozone is a triatomic [O₃] aliotrope (a substance that exists in many forms) of oxygen. It's a blue gas with a pungent odour that's extremely toxic to living things.
It occurs in the stratosphere of the atmosphere, but not in the lower atmosphere area known as the troposphere, and therefore has no lethal impact on life forms. If its value in the atmosphere rises to a significant level, it may become fatal, i.e., poisonous, and destroy all living things.

Question 4:  One of the following factors does not lead to soil formation in nature

(a) the sun                    

(b) Water                  

(c) Wind                   

(d) Polythene bags

Solution 4:  (d) Polythene bags. 

Soil is made up of rocks that have undergone the following processes:

(a) Weathering (breaking down of larger rocks into smaller mineral particles) and

(b) Paedogenesis (bacterial decomposition).
Polythene bags are a form of plastic that is not biodegradable. Since they can't be broken down by paedogenesis or weathering (physical, chemical, or biological), they don't help to shape soil. Aside from these, the soil's main non-degradable contaminants.

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  

Solution 5:   (c) ozone and oxygen. 

Our atmosphere contains oxygen in the form of a diatomic molecule. It is found in the troposphere in approximately 20.93 percent of the time (percentage of volume). Oxygen is required by living beings for respiration and material combustion (combustion). Its proportion in air is balanced by photosynthesis.
Ozone is an oxygen aliotrope found in large amounts in the stratosphere. It has a pungent odour and is a triatomic blue gas. The ozone layer is important because it filters out the sun's high-energy UV rays. Ozone is split into molecular and atomic oxygen by these rays.

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

(a) molecular form of hydrogen                 

(b) Elemental form of oxygen

(c) water                                                          

(d) Elemental form of nitrogen

Solution 6:  (b) Elemental form of oxygen.

Certain bacteria such as Azotobacter (occur freely in the soil) and Rhizobium (occur in root nodules of leguminous plants as pea, gramme, bean, etc.), turn the atmospheric nitrogen into water soluble nitrates. Nitrogen fixation is the term used to describe the mechanism of biofixing nitrogen.
Nitrogenases are enzymes that are needed for nitrogen biofixation. Nitrogenases are extremely vulnerable to oxygen depletion. In the presence of oxygen, many bacteria stop producing enzymes. Many nitrogen-fixing bacteria thrive in anaerobic environments, respiring to reduce oxygen levels or binding oxygen to proteins such as leg haemoglobin.

Question 7:  Rainfall patterns depend on
(a) the underground water table
(b) the number of water bodies in an area
(c) the density pattern of human population in an area
(d) the prevailing season in an area

Solution 7:  (b) the number of water bodies in an area.

When the water sources in an area are heated during the day, a significant amount of water evaporates and goes into the air, which influences the rainfall pattern and amount.
Water vapour is also released into the environment as a result of biological activities. Because of the sunshine, this air is also heated. The water vapour is carried up by the hot air as it rises.
The air expands and cools as it rises. As a result of the cooling, water vapour in the air condenses into tiny water droplets. Water condensation is aided if certain particles, such as dust and other suspended particles, serve as the "nucleus" or core particle from which the drops form.

Condensation expands the water droplets after they have formed. When the drops have grown large enough and heavy enough, they fall as rain.

Question 8:  Among the given options, which one is not correct for the use of large amount of fertilisers and pesticides?
(a) They are eco-friendly
(b) They turn the fields barren after some time
(c) They adversely affect the useful component from the soil
(d) They destroy the soil fertility

Solution 8:  (a) They are eco-friendly. 

Long-term use of pesticides and fertilisers can deplete soil fertility and structure by destroying soil microorganisms that recycle nutrients throughout the soil. It also destroys earthworms, which are essential for the production of rich humus.

Question 9:  The nitrogen molecules present in air can be converted into nitrates and nitrites by
(a) a biological process of nitrogen fixing bacteria present in soil
(b) a biological process of carbon fixing factor present in soil
(c) any of the industries manufacturing nitrogenous compounds
(d) the plants used as cereal crops in field

Solution 9:  (a) a biological process of nitrogen fixing bacteria present in soil. 

Nitrogen gas makes up about 78 percent of our environment, and it's also found in essential molecules like proteins and nucleic acids (DNA and RNA). As a result, it is a necessary nutrient for all living things.
A biological process involving nitrogen-fixing bacteria may transform nitrogen molecules in the air into nitrates and nitrites (present in the soil or present in association with plants). (Also see question 6)

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

(a) evaporation                 

(b) Transpiration             

(c) Precipitation              

(d) Photosynthesis

Solution 10:  (d) photosynthesis. 

Evaporation, transpiration, and precipitation are some of the processes involved in the water cycle.

Question 11:  The term ‘water pollution’ can be defined in several ways. Which of the following statements does not give the correct definition?

(a) The addition of undesirable substances to water-bodies
(b) The removal of desirable substances from water-bodies
(c) A change in pressure of the water-bodies
(d) A change in temperature of the water-bodies

Solution 11:   (c) A change in pressure of the water-bodies. 

Water pollution is described as an undesirable change in the physical, biological, or chemical qualities of water that has a negative impact on aquatic life and renders the water unfit for usage. Water pollution is one of the world's most critical environmental issues.
Water pollution can be of following three forms-
(i)   Surface water pollution (or inland water pollution).
(ii)  Underground water pollution.
(iii) Marine water pollution.
Chemicals, bacteria, and physical or sensory changes such as elevated temperature and discoloration are among the pollutants that cause water contamination. Waterborne diseases are caused by pathogens.
Water pollution is caused by changes in physical and chemical properties of water, such as pH, electrical conductivity, temperature, and eutrophication (an increase in the concentration of chemical nutrients). Water contamination is not caused by changes in water pressure.

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

(a) Methane                                              

(b) Carbon dioxide

(c) Carbon monoxide                              

(d) Ammonia

Solution 12:   (d) Ammonia. 

The greenhouse effect is a mechanism in which thermal radiations from a planetary surface (for example, the earth) are absorbed by atmospheric greenhouse gases and re-radiated in all directions, resulting in an increase in the planet's overall temperature (earth). The four main gases that contribute to the greenhouse effect on the planet in terms of percentage contribution are:

(i) Water vapour 36-70%               

(ii) Carbon dioxide 9-26%

(iii) Methane 4-9%                           

(iv) Ozone 3-7%

Nitrous oxide (N₂0) and Chlorofluorocarbons (CFCs) are two other greenhouse gases.

Question 13:  Which Step is not involved in the carbon-cycle?         

(a) Photosynthesis                                

(b) Transpiration

(c) Respiration                                        

(d) Burning of fossil fuels

Solution 13:   (b) Transpiration. 

The steps involved in carbon cycle are-

Question 14: ‘Ozone hole’ means
(a) a large sized hole in the ozone layer
(b) thinning of the ozone layer
(c) small holes scattered in the ozone layer
(d) thickening of ozone in the ozone layer

Solution 14:  (b) thinning of the ozone layer. 

The ozone layer, ozonosphere, ozone umbrella, or ozone shield are all terms for the portion of the atmosphere that is rich in ozone. Farman discovered that the ozone layer had thinned over Antarctica in 1985. It was referred to as the ozone hole. Augestein discovered a similar but smaller hole over the arctic zone (1987).
It has increased in size since 2000, when it was just 13 million km2. Ozone levels in the atmosphere are measured using a spectrometer and expressed in Dobson Units (DU).

Question 15:  Ozone layer is getting depleted because of
(a) excessive use of automobiles
(b) excessive formation of industrial units
(c) excessive use of manmade compounds containing both fluorine and chlorine
(d) excessive deforestation

Solution 15:   (c) excessive use of manmade compounds containing both fluorine and chlorine.

Reduction in the concentration of ozone layer is termed ozone depletion. It is caused by some chemicals which are usually rich in some of the chlorine, fluorine and carbon and are called Ozone Depleting Substances (ODS). Chlorofluorocarbons (CFCs), halones, methyl bromide, nitrogen oxides, Carbon Tetra Chloride (CCI₃), and dichlorodifuoromethane are just a few examples of important ODSs.
CFCs are widely used as aerosol propellants, refrigerants, shaving foams, and fragrance spray agents, among other things. Jets operating at high altitudes release some OD into the stratosphere.

Question 16:  Which of the following is a recently originated problem of environment?

(a) Ozone layer depletion               

(b) Greenhouse effect

(c) Global warming                          

(d) All of these

Solution 16:   (d) All of these.

Various toxic gases such as S0₂, C0₂, CO, CFCs, H₂S, HCN, and others are released into the environment as a result of widespread usage of vehicles and thermoelectric plants, gaseous emissions from industries, and the use of aerosol propellants, refrigerants, shaving foams, and spray agents, among other things..
These gases are significant contributors to air pollution and are intertwined in the degradation of the ozone layer, the greenhouse effect, and global warming.

Question 17:  When we breathe in air, nitrogen also goes inside along with oxygen. What is the fate of this nitrogen?
(a) It moves along with oxygen into the cells
(b) It comes out with the C0₂ during exhalation
(c) It is absorbed only by the nasal cells
(d) Nitrogen concentration is already more in the cells so it is not at all absorbed.

Solution 17:   (b) It comes out with the C0₂ during exhalation.

Elemental nitrogen in the atmosphere can't be used directly by plants or animals, so it has to be reduced before it can be used by higher plants and animals. Lightning-induced nitrogen fixation results in small amounts of ammonium and nitrate in precipitation.
Nitrogenase enzymes are found in many bacteria that can fix atmospheric nitrogen into an ammonium ion that is chemically useful to higher species.

Question 18:  Top soil 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

Solution 18:   (d) Humus, living organisms and soil particles.

The word "soil profile" refers to the vertical portion of the earth's crust made up of a series of horizontal layers known as horizons that vary in thickness, colour, texture, structure, consistency, porosity, acidity, and composition. The top soil, also known as the A-horizon, comprises the majority of the litter living organisms and humus. It also has a leaching region, which allows dissolved materials to drain downward. Tiny plants have their roots buried in the top soil. Mineral soil makes up the second horizon, or B-horizon (sub soil).

The unconsolidated parent material is found in the third, or C-horizon. The final horizon, referred to as the D-horizon, is made up of rock or unaltered parent material.

Question 19:  Choose the correct sequences
(a) C0₂ in atmosphere → Decomposers → Organic carbon in animals → Organic carbon in plants
(b) C0₂ in atmosphere → Organic carbon in plants → Organic carbon in animals → Inorganic carbon in soil
(c) Inorganic carbonates in → Organic carbon in plants Organic carbon in animals →  scavengers
(d) Organic carbon in animals → Decomposers → CO_;, in atmosphere → Organic carbon in plants

Solution 19:   (b) C0₂ in atmosphere → Organic carbon in plants → Organic carbon in animal’s → Inorganic carbon in soil.

Question 20:  Major source of mineral in soil is the
(a) parent rock from which soil is formed
(b) plants
(c) animals
(d) bacteria

Solution 20:  (a) parent rock from which soil is formed.

Soil formation is aided by the physical and chemical weathering of rocks. Natural soil aggregates with one or more minerals or mineraloids are known as rocks. The minerals quartz, feldspar, and biotite, for example, make up traditional granite.

Question 21:  Total earth’s surface covered by water is

(a) 75%                   

(b) 60%                     

(c) 85%                     

(d) 50%

Solution 21:   (a) 75%.

Water is essential for all known forms of life and covers approximately 75% of the earth's surface.  96.5 percent of the planet's water is found in seas and lakes, 17% in groundwater, 1.7 percent in glaciers and ice caps, and 0.001% in the atmosphere as water vapour, clouds, and precipitation.
Freshwater makes up only 2.5 percent of the earth's water, with the remaining 98.8% in ice and groundwater. Surface water (rivers, lakes, cakes, and ponds) and soil water are responsible for the remainder.

Question 22:  Biotic component of biosphere is not constituted by

(a) producers         

(b) Consumers         

(c) Decomposer      

(d) Air

Solution 22:   (d) air.

The biosphere is the global sum of all ecosystems, encompassing all living things and their interactions with the lithosphere (land), hydrosphere (water), and atmosphere (air).

The biosphere is made up of-
(i) Biotic Components- Biotic Components are the living organisms that contribute to the formation of an ecosystem. Producers, consumers, and decomposers are common biotic components.
(ii)  Abiotic Components- The non-living chemical and physical components of the environment, such as air, water, soil, temperature, and sunlight, are known as abiotic components.

Question 23:  An increase in carbon dioxide content in the atmosphere would not cause
(a) more heat to be retained by the environment
(b) increase in photosynthesis in plants
(c) global warming
(d) abundance of desert plants

Solution 23:  (d) abundance of desert plants.

Increased carbon dioxide levels in the atmosphere will not result in more desert plants because their ability to absorb carbon dioxide decreases as temperature increases (due to increased carbon dioxide emissions).

Question 24:  Oxygen is returned to the atmosphere mainly by

(a) burning of fossil fuel                         

(b) Respiration

(c) photosynthesis                                   

(d) Fungi

Solution 24:   (c) photosynthesis.

CO₂ is emitted into the atmosphere as fossil fuels are burned. Photosynthesis is the mechanism by which plants make their food in the presence of carbon dioxide and sunlight, resulting in oxygen in the atmosphere.

Question 25:  Low visibility during cold weather is due to
(a) formation of fossil fuel
(b) unburnt carbon particles or hydrocarbons suspended in air
(c) lack of adequate power supply
(d) None of the above

Solution 25:  (b) unburnt carbon particles or hydrocarbons suspended in air.

The volume of suspended particles in the air increases as a result of the burning of fossil fuels.

It's possible that the suspended particles are unburned carbon particles (i.e., hydrocarbons). When these pollutants are present in high concentrations, visibility is reduced, particularly in cold weather when water condenses out of the air. This is referred to as smog, and it is a noticeable sign of pollution in the air.

Question 26:  Growth of lichens on barren rocks is followed by the growth of

(a) moss                                                    

(b) Ferns

(c) gymnosperms                                    

(d) Algae

Solution 26:   (a) moss.

Lichens are the forerunners of succession, producing acid to erode the barren soil, and so on.

The majority of lichens can be found on solid rock surfaces or on the bark of old trees. They are an essential component of soil stabilisation and aid in water retention. This allows masses to develop on the soil after lichen, and gymnosperms to follow.

Question 27:  Marked temperature changes in aquatic environment can affect

(a) breeding of animals                            

(b) More growth of aquatic plants

(c) process of digestion in animals        

(d) Availability of nutrients

Solution 27:   (a) breeding of animals.

The majority of aquatic animals are cold blooded, which means that their body temperature varies depending on the environment; however, aquatic animals' eggs and larvae are especially vulnerable to temperature changes.

Question 28:  Soil erosion can be prevented by

(a) raising forests                                     

(b) Deforestation

(c) excessive use of fertiliser                  

(d) Overgrazing by animals

Solution 28:   (a) raising forests.

The following are some of the techniques used to avoid soil erosion:

1. Cropping on a large scale Crops help to tie the soil.
2. Planting xerophytes and sowing grasses Planting xerophytes or sowing grasses on barren soil can tie the loose soil.
3. Planting on terraces (terracing) To slow the flow of water, terracing divides the hills into a variety of flat fields. Furthermore, eroded soil from hills' upper regions is deposited in lower terraces.
4. Bundling on the contour on the edges of fields, small bunds (embankments or dikes) are elevated to avoid top soil loss due to wind or water.
5. Tillage for conservation Reduced or no tillage may be used instead of traditional tillage.
6. Breaks in the wind Trees and shrubs are planted in rows perpendicular to the prevailing wind direction.
7. Drainage canals around the fields that are in good condition. This approach entails draining excess rainwater into small drainage canals that have been created across the fields.

Question 29:  What happens when rain falls on soil without vegetation cover?
(a) Rain water percolates in soil efficiently
(b) Rain water causes loss of surface soil
(c) Rain water leads to fertility of the soil
(d) Rain water does not cause any change in soil

Solution 29:   (b) Rain water causes loss of surface soil.

The presence of vegetation on the field aids in the stabilisation of the soil. It also aids in the percolation of water into the soil's deeper layers. Soil erosion can occur when vegetation isn't present.

Question 30:  Oxygen is harmful for

(a) ferns                                                   

(b) Nitrogen fixing bacteria

(c) Chara                                                   

(d) Mango tree

Solution 30:  (b) nitrogen fixing bacteria.

Anaerobic environments, or the lack of oxygen, are where nitrogen-fixing bacteria can be found.

Short Answer Type Questions.............................

Question 31:  Rivers from land, add minerals to sea water. Discuss how?

Solution 31:   The soil is made up of rocks (which are accumulation of minerals) (which are aggregation of minerals). Due to heavy rains and hoods the unprotected top soil gets washed into the streams and rivers. The top soil in the fields and along the river banks is washed away by the swift flowing water. Almost all rivers, along with eroded soil and mineral particles, end up in oceans and seas, adding to their mineral content.

Question 32:  How can we prevent the loss of top soil?

Solution 32:   Humus, earthworms, and other living species make up top soil. Excessive waves, flooding, rainwater, and other natural disasters are the major causes of loss. Deforestation, desertification, and other factors are significant contributors to soil erosion (loss of top soil). Various techniques, such as contour farming and afforestation, may be used to avoid it.

(Refer to Q. 28 as well.)

Question 33:  How is the life of organisms living in water affected when water gets polluted ?

Solution 33:   Almost all types of water pollution have an effect on aquatic life. Pollutants promote the growth of certain life forms while hindering the growth of others. This has an effect on the balance of species that survive in that environment (ecosystem). Bacteria grow rapidly as the amount of organic waste in water increases, consuming all usable oxygen. Fish and other marine species die as a result of the lack of oxygen.

Aquatic species are used to a certain temperature range in the water body in which they live; a drastic shift in this temperature (they are cold-blooded animals) can be extremely dangerous to them, affecting, for example, aquatic animal breeding.

Question 34:  During summer, if you go near the lake, you feel relief from the heat, why?

Solution 34:   We are relieved from the heat since the high-pressure air over the lake blows into the low pressure air over ground. As opposed to the air over the ground, the air over the lake is significantly cooler.

Question 35:  In coastal area, wind current moves from the sea towards the land during day; but during night it moves from land to the sea. Discuss the reason.

Solution 35:   During the day, there is a steady flow of cool air from the sea to the land in coastal areas. There is a reverse migration of air from land to sea at night. This occurs because land heats up faster than water during the day and the radiated heat from land heats the air above it. The hot air rises, creating a low-pressure zone.
Since sea water does not heat up as quickly as air, the air above the sea is relatively cold. In comparison to air over ground, a high-pressure area develops above sea level.

As a result, cooler air from the sea flows into the land (low-pressure area). Winds are generated by the passage of air from one location to another. 

During the night, there is a reverse flow of air. The soil cools quickly, and the air above it cools as well. Since sea water cools slowly, the air above it is cooler and has a lower air pressure than the air above the land. As a result, cooler air from the ground flows into the sea.

Movement of wind from sea to land during day and from land to sea during night

Question 36:  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 from making soil.

Solution 36:  (a) Lichens can grow on rocks and are one of the species mentioned above. They release substances that cause the rock surface to powder down and form a thin layer of soil during their development. Lichens are microscopic organisms that grow on the surface of rocks and extract minerals. Small crevices form where a thin layer of soil has accumulated.
Mosses develop over these crevices, causing the crevices to deepen and more soil to accumulate within. When the roots of short-lived herbs move through deeper crevices, cracks develop, and cracks grow wider and deeper.
The roots of larger plants (e.g., peepal, banyan tree) migrate through the cracks over time. Cracks expand over time, causing rock fracturing and ultimately pulverisation.

Question 37:  Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?

Solution 37:   The following are some of the abiotic factors that play a role in soil formation:]

(a) Rocks                                                   

(b) Water

(c) Sun                                                       

(d) Wind

The following biological factors play a role in soil formation:

(a) Lichens  

(b) Bryophytes

(c) Bacteria                                                

(d) Fungi

(e) Nematodes                                         

(f) Earthworm

(g) Arthropods

e.g., ants.

Question 38:  All the living organisms are basically made up of C, N, S, P, H and 0. How do they enter the living forms? Discuss.

Solution 38:   Plants enable elements such as carbon, nitrogen, sulphur, phosphorus, hydrogen, and oxygen to enter living forms. During photosynthesis, the majority of these elements joins plants and become part of their organic material. These components are passed down the food chain from plants to other species. Plants (grasses) are consumed by goats, which are then consumed by humans. As a result, organic materials move from grass to goat and then to man.

Question 39:  Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?

Solution 39:   The percentage of gases such as oxygen, nitrogen, and carbon dioxide in the atmosphere is preserved by their cyclic flow.

The oxygen, nitrogen, and carbon cycles all function continuously in nature due to the continual interaction between the biosphere's biotic and abiotic components. These interactions include the exchange of matter and energy among the biosphere's various components.

As a result, their levels in the atmosphere are kept steady and within acceptable limits.

Question 40:  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?

Solution 40:   The moon and the earth are at the same distance from the sun, but there are extreme temperature differences, ranging from -190°C to 110°C. The lack of an atmosphere on the moon is the primary cause of its extreme temperature variations. The environment plays a critical role in temperature regulation. Since air is a poor conductor of heat, it serves as a temperature buffer, preventing excessive warming during the day and excessive cooling during the night.

Question 41:  Why do people love to fly kites near the seashore ?

Solution 41:   During the day, the air above the land in seashore or coastal regions heats up faster and rises. When the air rises, a zone of low pressure forms, and air from the sea flows into it.
Winds are generated by the passage of air from one area to another. The wind will be blowing from the sea to the land during the day. As a result, flying kites near the seashore is much easier than anywhere else. (Refer to 0. 35 as well.)

Question 42: Why does Mathura refinery pose problems to the Taj Mahal ?

Solution 42:  The Mathura refinery emits a variety of contaminants into the atmosphere, including sulphur dioxide. Sulphuric acid is formed when S02 reacts with water in the atmosphere. Rain washes out the sulphuric acid into the soil (acid rainfall). This acid erodes stone, affects salmon reproduction, and damages brickwork, among other things.

As a result, they pose a significant threat to the Taj Mahal, as they have the ability to degrade the consistency and colour of the marble, among other things.

Question 43:  Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?

Solution 43:  Lichens are bio-indicators of emissions in the air. Sulphur dioxide (S0₂) emissions in the air from cars and other factories are extremely harmful to them. In comparison to Manali and Darjeeling, Delhi has the highest level of air pollution due to the large number of vehicles. As a result, lichens do not flourish in Delhi or any other city with high levels of air pollution.

Question 44:  Why does water need conservation even though large oceans surround the land masses?

Solution 44:   Water is one of the most unique natural compounds on the planet, as well as a vital component of life. Snow, water, and water vapour are all forms of it. Terrestrial life forms need fresh water to survive, and fresh water is difficult to come by.

(Refer to Q. 21 as well.)

Question 45:  There is mass mortality of fishes in a pond. What may be the reasons?

Solution 45:   Water contamination may be the cause of mass fish mortality in a pool.

(Refer to Q.33 as well.)

Question 46: Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil?

Solution 46:  Lichens is a type of lichen that grows on the surface of rocks and extracts minerals from them. This results in small crevices where a thin layer of soil has built up.

(Refer to Q. 36 as well.)

Question 47:  ‘Soil is formed by water.’ If you agree to this statement then give reasons.

Solution 47:  The breakdown of larger rocks into smaller mineral particles is aided by water. It could get into cracks in the rocks caused by uneven sun heating. If this water freezes, it will widen the cracks.
And hard rock can be worn away by flowing water over time. Large and small rock fragments are often carried downstream by fast-moving water. These rocks collide with other rocks, causing the rock to break down into smaller and smaller fragments as a result of the abrasion. These particles are then carried by the water and deposited elsewhere.

Question 48:  Fertile soil has lots of humus, why?

Solution 48:  Since it includes microorganisms that decompose dead organic matter in the soil and aid in the production of humus, fertile soil has a lot of it. Flume is a mineral source that absorbs water and makes the soil porous for plant roots to move through easily.

Question 49:  Why step farming is common in hills?

Solution 49:   Step farming is a common method of preventing soil erosion due to rain and strong winds.

(Refer to Question 28 as well.)

Long Answer Type Questions..........................

Question 50:  Why are root nodules useful for the plants?

Solution 50:   Root nodules are special parts of plants' roots that contain nitrogen-fixing bacteria. These bacteria convert inert aerial nitrogen into nitrates for the use of plants. Nitrogen fixation refers to the process of nitrogen being bio fixed by bacteria such as Rhizobium.

Question 51:  How do fossil fuels cause air pollution?

Solution 51:   The introduction of particulate matter, gases, and vapours into the atmosphere causes air pollution, which has a negative impact on humans, animals, vegetation, and human assets. There are two types of air pollution:

1. Natural (e.g., forest fire, dust storm, pollen);

2. Human made (e.g., burning of fossil or fuels in industries, vehicles and thermoelectric plants, gaseous emission from industries, mining processing, stone crushing).
Because particulate air pollutants stay suspended in the air for a long time, they are also known as suspended particulate matter or SPM. SPM is made up of smokes, soot (a black powder substance produced when coal, wood, and other materials are burned), fly ash, and dust (i.e., particles of silica, grit, lead, asbestos, cement, sulphur, etc.).
Sulfur dioxide, nitrogen oxides, carbon monoxide, hydrogen sulphide, hydrogen cyanides, hydrogen fluorides, arsenic, methane, and ammonia are gases that pollute the air. They're made up of nitrogen, sulphur, and carbon compounds that come from fossil fuels and decomposing organic matter. Unburned hydrocarbons are among the pollutant vapours (benzene).

Question 52:  What are the causes of water pollution? Discuss how you can contribute in reducing water pollution.

Solution 52:   The following are some of the various sources of air pollution:

(i) Industrial wastes Mill and industry effluents, such as those from paper mills and petroleum refineries, contain vast amounts of toxic chemicals such as acids, alkalis, and heavy metals (e.g., mercury salts from paper industries). These contaminants are dumped into bodies of water (rivers and lakes).
(ii) Synthetic soaps and detergents Soap and detergent-contaminated water is discharged into rivers from homes and factories.
(iii) Fertilisers and pesticides In order to improve crop yield, fertilisers and pesticides are used excessively in the fields. Rainwater washes these into bodies of water, polluting them.      .
(iv) Petroleum oil In the oceans, drilling and shipping operations are normal. Water contamination occurs when petroleum oil leaks during such activities or as a result of incidents (e.g., an oil spill).
(v) Solid particles Rain erodes soil and transports silt to bodies of water. Clay and dust particles suspended in the water settle as well. Turbidity in water is caused by these soil particles.
(vi) Thermal pollution The discharge of hot water from factories and thermal plants into bodies of water alters the water's natural temperature. The amount of oxygen in the atmosphere decreases. Reduced oxygen levels destroy marine organisms and slow the decomposition of organic matter, causing it to accumulate.
(vii) Sewage Food processing plants, dairy farms, piggeries, poultry farms, slaughterhouses, breweries, tanneries, and other businesses contribute organic waste as domestic and industrial sewage. Animal excreta deposited in pits or discharged into fields enter water bodies via runoff and leaching, causing water pollution, particularly during the rainy season.

Water emissions can be reduced in the following ways:

(i) If sewage and garbage created by homes and factories are properly handled before being discharged into water bodies, water contamination will be reduced and marine life will be less harmed.

(ii) The breeding ability of aquatic species will not be harmed if hot water provided by factories is collected in a common area, allowed to cool, and then discharged in water bodies.

(iii) It is possible to reduce the impact of air pollution on people if commercial fields, factories, and manufacturing are relocated to a remote location away from residential areas.

Question 53:  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?

Solution 53:   UV rays are emitted by the sun, which pass through the glass and heat the vehicle. The heat trapped inside increases the temperature of the interior because the radiations produced by inner parts cannot move through the glass.
This is due to the fact that glass is transparent to infrared rays emitted by the sun, which have a shorter wavelength than those emitted by the interior of the car, which have a longer wavelength, and to which the car's glass is opaque.

Question 54:  Justify ‘Dust is a Pollutant.

Solution 54:   Dust is a pollutant for the following reasons:

(i) Dust is made up of suspended spores. Dust inhalation can cause a variety of problems, including allergic asthma, bronchitis, a cold, or a cough.

(ii) It decreases light intensity.

(iii) Dust particles settle on leaves, blocking stomata and reducing plant gaseous exchange.

(iv) It irritates the eyes.

(v) Plant photosynthetic activity is reduced by dust particles.

(vi) It contains pollutants such as smoke, fly ash, silica particles, lead, asbestos, and so on, which pollute the atmosphere.

Question 55:  Explain the role of the sun in the formation of soil.

Solution 55:   During the day, the sun heats up the rocks, causing them to grow. These rocks cool down and contract at night. Since not all rock parts expand and contract at the same pace (ultimately huge rocks break into smaller pieces). Soil is formed as a result of this process.

(Refer to Q. 37 as well.)

Question 56:  Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?

Solution 56:   For plants to perform photosynthesis, carbon dioxide gas is needed. It also contributes to global warming. It is both a good raw material and an imperative for keeping the earthworm alive up to a certain concentration1 in the atmosphere (approximately 350 ppm). However, when the concentration of CO₂ exceeds a certain threshold, it becomes a pollutant. This is what causes the greenhouse effect. It can cause a variety of respiratory problems and contributes to the development of smog.