NCERT Exemplar Class 9 Science Solutions Chapter 14 Natural Resources

NCERT Exemplar Class 9 Science Solutions Chapter 14

Given below are the solved questions and answers of different types like MCQs and short and long answers that increase the clarity and knowledge of the concepts and make you familiar with the types of questions that can come in an exam so that you can answer them with confidence and skill.

Discover NCERT Exemplar Class 9 Science Solutions Chapter 14-MCQ

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
Answer: The correct answer is option (d), re-radiated by land and water.

Explanation: The Earth's atmosphere is heated mainly by the radiation that is re-radiated by both land and water. When sunlight reaches the Earth's surface, it is absorbed by land and water bodies. These surfaces then release heat in the form of infrared radiation, which warms the atmosphere.

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
Answer: The correct answer is option(c), increase during the day and decrease during the night

Explanation: Without the atmosphere, the earth would get extremely hot during the day due to direct sunlight and very cold at night as all the heat would escape quickly.

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.
Answer: The correct answer is option(b). It will become poisonous and kill living forms

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
Answer: The correct answer is option(d), Polythene bags

Explanation: Soil formation is a natural process caused by factors like the sun, water, and wind, which break down rocks into smaller particles. Polythene bags are non-biodegradable and do not contribute to soil formation. Instead, they harm the environment by polluting the soil.

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: The correct answer is option(c), ozone and oxygen

Explanation: Oxygen does not exist in atomic form. The two forms of oxygen found in the atmosphere are oxygen (O₂), which is essential for breathing, and ozone (O₃), which forms a protective layer in the upper atmosphere that blocks harmful UV 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
Answer: The correct answer is option (b), the elemental form of oxygen.

Explanation: Nitrogen-fixing bacteria, like Rhizobium, cannot perform nitrogen fixation in the presence of elemental oxygen (O₂) because it stops the enzyme nitrogenase, which is essential for the process. These bacteria can perform only in anaerobic conditions.

Question:7

Rainfall patterns depend on
(a) the underground water tables
(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
Answer: The correct answer is option (b), the number of water bodies in an area

Explanation: Rainfall patterns depend on the number of water bodies in an area because large water bodies like lakes and rivers increase moisture in the atmosphere through evaporation, which leads to cloud formation and thus increases the rainfall.

Question:8

Among the given options, which one is not correct for the use of large amount of fertilizers 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
Answer: The correct answer is option(a); they are eco-friendly.

Explanation: Large amounts of fertilizers and pesticides are not eco-friendly. They harm the environment, reduce soil fertility, and kill useful microorganisms in the soil, leading to barren fields.

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
Answer: The correct answer is option(a)

Explanation: Nitrogen fixation process converts nitrogen present in atmosphere into nitrogen compounds.Nitrogen-fixing bacteria, like Rhizobium, convert nitrogen from the air into nitrates and nitrites, which plants can absorb and use for growth. This process is essential for maintaining soil fertility.

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
Answer: The correct answer is option(d), Photosynthesis

Explanation: Photosynthesis is the process by which plants make their food using sunlight, water, and carbon dioxide. It is not a step of the water cycle, which involves evaporation, transpiration, condensation, and precipitation.

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
Answer: The correct answer is option(c), a change in pressure of the water bodies

Explanation: Water pollution refers to the addition of harmful substances, removal of essential nutrients, or temperature change in water bodies such as Lakes, ponds, rivers, ocean, underground water etc. that harm aquatic life. A change in pressure is not a standard definition of water pollution.

Question:12

Which of the following is not a greenhouse gas?
(a) Methane
(b) Carbon dioxide
(c) Carbon monoxide
(d) Ammonia
Answer: The correct answer is option(d), Ammonia

Explanation: Ammonia (NH₃) is not a greenhouse gas. Greenhouse gases are those gases which contribute in greenhouse effect. Greenhouse gases like methane (CH₄) and carbon dioxide (CO₂) trap heat in the atmosphere, but ammonia mainly contributes to air pollution, not global warming.

Question:13

Which step is not involved in the carbon-cycle?
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Burning of fossil fuels
Answer: The correct answer is option(b), Transpiration

Explanation: Transpiration is the process of the removal of water vapor from plants through leaves, and it is part of the water cycle, not the carbon cycle. It does not involve emission or absorption of carbon dioxide.The carbon cycle involves photosynthesis, respiration, and the burning of fossil fuels.

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
Answer: The correct answer is option(b), Thinning of the ozone layer

Explanation: The Ozone layer around the earth is very much required for life on earth. This layer is getting depleted by man-made compounds containing fluorine chlorine etc. The thinning of the ozone layer refers to the ozone hole that allows harmful UV rays of the sun to reach the Earth.

Question:15

Ozone-layer is getting depleted because of
(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: The correct answer is option(c)

Explanation: The ozone layer is depleting due to chlorofluorocarbons (CFCs) and other man-made compounds that contain fluorine and chlorine that are released from refrigerators. The thickness of ozone layer is decreasing at many part around the earth. The ozone layer around the earth is very much required for life on earth.

Question:16

Which of the following is a recently originated problem of environment?
(a) Ozone layer depletion
(b) Green house effect
(c) Global warming
(d) All of the above
Answer: The correct answer is option(d), All of the above.

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$C{O}_2$ 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.
Answer: The correct answer is option(b). It comes out with the carbon dioxide during exhalation.

Explanation: Nitrogen is inhaled with oxygen but is not used by the body because it is not needed for respiration. It remains unchanged and is exhaled along with carbon dioxide. Nitrogen is the most abundant gas in nature, so it enters the body but also comes out.

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.
Answer: The correct answer is option(d), Humus, living organism, and soil particles.

Question:19

Choose the correct sequences
(a) $C{O}_2$ in atmosphere → decomposers → organic carbon in animals → organic carbon in plants
(b) $C{O}_2$ in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil
(c) Inorganic carbonates in water → organic carbon in plants → organic carbon in animals → scavengers
(d) Organic carbon in animals → decomposers $C{O}_2$ in atmosphere → organic carbon in plants
Answer: The correct answer is option(b)

Question:20

Major source of mineral in soil is the
(a) parent rock from which soil is formed
(b) plants
(c) animals
(d) bacteria
Answer: The correct answer is option(a), parent rock from which soil is formed.

Explanation: All soils initially come from rocks; this is termed the ‘parent material. ’ The Parent Material may be directly below the soil or great distances away if wind, water, or glaciers have transported the soil. The formation of soil can be seen as a combination of the products of weathering and other processes.

Question:21

Total earth’s surface covered by water is
(a) $71\mathrm{\%}$
(b) $60\mathrm{\%}$
(c) $85\mathrm{\%}$
(d) $50\mathrm{\%}$
Answer: The correct answer is option(a), 71%

Question:22

Biotic component of biosphere is not constituted by
(a) producers
(b) consumers
(c) decomposer
(d) air
Answer: The correct answer is option(d), air

Explanation: Biotic components include living organisms such as plants, animals, and humans. All the other factors, such as water, sunlight, air, and soil, are considered abiotic factors. Abiotic factors refer to non-living physical and chemical elements in the ecosystem.

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
Answer: The correct answer is option (d), abundance of desert plants

Question:24

Oxygen is returned to the atmosphere mainly by
(a) burning of fossil fuel
(b) respiration
(c) photosynthesis
(d) fungi
Answer: The correct answer is option(c), photosynthesis

Explanation: Oxygen is returned to the atmosphere mainly by the process of photosynthesis, as in this process, plants use carbon dioxide, water, and sunlight to prepare food and release oxygen and sugar. This oxygen is returned to the atmosphere and utilized by humans and animals. Respiration is a catabolic process while photosynthesis is an anabolic process. During respiration oxygen is taken and carbon dioxide is given out while during photosynthesis carbon dioxide is taken and oxygen is given out.

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 these
Answer: The correct answer is option(b), unburnt carbon particles or hydrocarbons suspended in air

Explanation: Low visibility during cold weather is due to smog, which consists of unburnt particles of carbon or hydrocarbons that are present in the air. It causes air pollution and is released from vehicles and industries. The exhaust from diesel vehicles contain unburnt carbon particles and hydrocarbons that also cause pollution.

Question:26

Growth of Lichens on barren rocks is followed by the growth of
(a) moss
(b) ferns
(c) gymnosperms
(d) algae
Answer: The correct answer is option (a), moss

Question:27

Aquatic organisms are used to a certain range of temperature in the water bodies where they live. 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.
Answer: The correct answer is option(a), breeding of animals.

Explanation: Aquatic animals are highly susceptible to temperature changes. To lay eggs aquatic animals need optimum temperature. Thus, any temperature change affects the breeding process.

Question:28

Soil erosion can be prevented by
(a) raising forests
(b) deforestation
(c) excessive use of fertilizer
(d) overgrazing by animals
Answer: The correct answer is option(a), raising forests

Explanation: Soil erosion refers to the removal of topsoil by the wind, water, or any other factors. To reduce the soil erosion, more plants and trees need to be grown as the roots of the plants hold the soil and do not carry it away by wind or water.

Question:29

What happens when rain falls on soil without vegetational 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
Answer: The correct answer is option(b), rain water causes loss of surface soil

Explanation: Soil erosion refers to the wearing away of a field's topsoil by the natural physical forces of water. When rain falls on soil without vegetational cover, rainwater causes the loss of surface soil or topsoil. Topsoil, which is high in organic matter, is washed off by the wind or water.

Question:30

Oxygen is harmful for
(a) ferns
(b) nitrogen fixing bacteria
(c) chara
(d) mango tree
Answer: The correct answer is option(b), nitrogen-fixing bacteria.

Explanation: The process of nitrogen fixation occurs when atmospheric nitrogen is converted to ammonia by a Nitrogenase enzyme. Nitrogenases are rapidly degraded by oxygen. For this reason, many nitrogen-fixing organisms exist only in anaerobic conditions and fix atmospheric nitrogen.

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Question:31

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

Minerals from the land reach the sea by the process of weathering and erosion of rocks, which releases minerals. When rain falls on soil, these minerals are carried by rainwater into rivers, and after that, they reach the ocean. Once it reaches the sea, the minerals dissolve and spread, providing nutrients that support marine life.

Question:32

How can we prevent the loss of top soil?
Answer:

We can’t completely eliminate soil erosion, but we can reduce the loss of top soil by taking simple steps. Planting trees and grass keeps the soil in place because the roots of the plants hold the soil together. Farmers can protect the soil by changing crops and plowing in a way that stops soil from washing away. Covering empty soil with leaves or other materials also slows down water and keeps the soil safe. These steps help keep the soil healthy and ready for growing plants.

Question:33

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

When water gets polluted, it harms the organisms present in it. Dirty water reduces the amount of oxygen that fish and other animals need for their survival. Harmful chemicals and waste can poison the water, and some pollutants are synthetic and do not degrade easily, making them unsafe for plants and animals.. Over time, many aquatic animals may die, and the balance of life in the water is disturbed. The effect of pollution on water is huge, and it affects all the species living there.

Question:34

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

During summer, when we go near a lake, we feel relief from the heat because the air around the water gets cooled. Water, in comparison to the land, gets heated and cooled more slowly, due to which the air near the water gets cooled, which is known as a land breeze and makes the temperature low, due to which we feel good and cool near the lake.

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.
Answer:

The reason for this process is land and sea breeze. A land breeze is created when the land is cooler than the water, such as at night, and the surface winds have to be very light. When this happens, the air over the water slowly begins to rise. As the air begins to rise, the air over the surface of the ocean has to be replaced; this is done by drawing the air from the land over the water.

A sea breeze is created when the surface of the land is heated sufficiently to start the rising of the air. As air rises, it is replaced by air from the sea. Sea breezes tend to be much stronger and can produce gusty winds as the sun can heat the land to very warm temperatures, thereby creating a significant temperature contrast to the water. So that is the reason wind current moves from the sea towards the land during day; but during night it moves from land to the sea.

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 for making soil.
Answer:

Organisms that can colonize bare rock are called pioneer species. Among the organisms mentioned, lichens and mosses can grow on stones and help in the formation of soil. Lichens are usually the first pioneer species, and they look like white, green, grey, yellow, or even orange. Mosses are plants that don't have flowers or stems or roots - just tiny green leaf-like structures.
Lichens release certain acids that break down the surface of the rocks. This process turns the rock into small particles. After some time, lichens and mosses die and decay, and they mix with these particles to create the first layer of soil. This slow process helps in the formation of fertile soil, which supports the growth of larger plants like mango trees, etc.

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?
Answer:
Abiotic factors involved in soil formation are
(a) Rocks
(b) Water
(c) Sun
(d) Wind
Biotic factors involved in soil formation are
(a) Lichens
(b) Bryophytes
(c) Bacteria
(d) Fungi
(e) Nematodes
(f) Earthworm
(g) Arthropods

Question:38

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

All living organisms are mainly made up of carbon (C), nitrogen (N), oxygen (O), hydrogen (H), phosphorus (P), and sulfur (S). These elements enter living organisms through a cyclic path that is from environment to living organisms and back to the environment. These circular paths are called biogeochemical cycles or nutrient cycles.
Plants absorb carbon from the air as carbon dioxide during photosynthesis. They take nitrogen and phosphorus from the soil through their roots. Water, which contains hydrogen and oxygen, is also absorbed by plants. Herbivores and consumers get these elements by eating plants or other animals. In this way, they enter into the body of living organisms.

Question:39

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

The percentage of gases like oxygen, nitrogen, and carbon dioxide remains the same in the atmosphere because of a natural balance. The movement of oxygen, nitrogen, and carbon dioxide between the atmosphere and the biosphere results in maintaining a constant amount of these compounds in the atmosphere over time. For example, Plants take carbon dioxide during the process of photosynthesis to prepare food and release oxygen, while animals and humans take that oxygen and release carbon dioxide. Nitrogen stays stable because it is recycled through the nitrogen cycle, where it moves between the air, soil, and living things. These natural processes work together to maintain a balance of gases in the atmosphere, making sure that the air remains suitable for all living organisms.

Question:40

Why does moon have very cold and very hot temperature variations eg, from $-{190}^{\circ }C$ to ${110}^{\circ }C$even though it is at the same distance from the sun as the earth is?
Answer:

The atmosphere around the earth consists of many gases and particles, and it traps heat and spreads it, making the temperature balance, but the moon has no atmosphere around it, and due to which, it directly absorbs heat from the sun during the day making it hot and as heat does not remain trapped it becomes extremely cold.

Question:41

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

People love to fly kites near the seashore because the wind is strong and steady there. Near the seashore the land and sea breeze occurs. During the day, the land heats up faster than the sea, making the cool air move from the sea towards the land. This movement of air, called sea breeze, creates the perfect wind for flying kites. The open space near the shore also gives enough space for kites to get high without any trouble.

Question:42

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

The Mathura Refinery poses problems to the Taj Mahal because it burns fossil fuels, which releases soot and harmful gases like sulfur dioxide and nitrogen dioxide into the air. These gases then mix with moisture in the air and form acid rain. When acid rain falls, it reacts with the marble of the Taj Mahal, causing its discoloration. This process, called marble cancer, damages the beauty of the monument.

Question:43

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

Lichens are called as bioindicators of air pollution. They are sensitive to air pollution, especially with harmful gases like sulphur dioxide, and cannot survive in bad air quality. Delhi, due to a large number of vehicles, factories using fossil fuels, etc, causes air pollution and releases many gases that are harmful to the environment, whereas in Manali and Darjeeling, the air is fresh and clean, which allows lichens to grow easily.

Question:44

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

Water still needs to be conserved even though the earth is surrounded by large oceans because only 2.5% of the earth’s water is freshwater, and out of this, most of the water is trapped in glaciers or underground. Only 0.5% of the amount of freshwater is available for human use, and with a growing population, the need for water is also increasing and salty water can not be utilized by humans for drinking. Thus, water conservation is important because fresh clean water is a limited resource, as well as a costly one.

Question:45

There is mass mortality of fishes in a pond. What may be the reasons?
Answer:
One reason for the mass mortality of fishes in a pond is eutrophication. Eutrophication is a process by which plant growth increases in a water body like ponds or lakes. The increased growth and overcrowding of plants is due to either natural fertilizing agents that are washed off from the soil or the runoff of chemical fertilizers applied to agricultural lands. As the overcrowd plants die off, the dead and decaying vegetation depletes the pond’s oxygen supply. This in turn leads to the mass scale death of fish in the pond.
Any change in the water quality necessarily influences the whole of surrounding environment. Hence to maintain a well-defined environment, the ecology of an ecosystem should not be disturbed. Some other reason may be Poor water quality, Poor pond hygiene, Presence of Pests, etc.

Question:46

Lichens are called pioneer colonizers of bare rock. How can they help in formation of soil?
Answer:

Lichens are called pioneer colonizers because they are the first organisms to grow on bare rocks. Lichens are usually white, green, grey, yellow, or even orange in colour. As lichen starts growing on a rock, there are chances of growing moss too. Lichens release acids that slowly break down the surface of the rock and divide it into small particles. These particles get mixed with the dead lichen and result in the formation of the first layer of soil. This thin layer allows other plants and mosses to grow and results in more fertile soil.

Question:47

“Soil is formed by water.” If you agree to this statement then give reasons
Answer:
The soil is made up of rocks (which are aggregation of minerals). Water plays an important role in the formation of healthy and productive soil. Soil is formed by the breaking of rock particles that contain soluble minerals over a long time. Water helps in the process of carrying small rock particles, causing erosion and helping in breaking rocks by repeated cycles of freezing and melting. Water also serves to bind and secure the physical particles in soil structure, and it is the medium through which essential nutrients are transported to plants. The importance of water cannot be overstated; in addition to sustaining all life on Earth it plays an important role in formation of soil.

Question:48

Fertile soil has lots of humus. Why?
Answer:

Fertile soil contains a lot of humus because fertile soil consists of water, air, organic matter, and nutrient minerals like nitrogen, phosphorus, and potassium, which are important for plant growth. Humus is formed from the decomposition of dead plants and animals. Humus contains many minerals, making the soil fertile and healthy and also helping to retain the moisture that increases plant growth.

Question:49

Why step farming is common in hills?
Answer:

Step farming, also known as terrace farming, is common in hilly areas because of its benefits. Mainly, this helps in the conservation of soil and water. In this method, the land is cut into steps or terraces, which slow down the flow of water and thus allow it to be absorbed by the soil. This helps in increasing the water holding capacity and nutrients, making the land more suitable for growing crops.

Question:50

Why are root nodules useful for the plants?
Answer:

Root nodules are small and rounded structures that are found on the roots of leguminous plants like peas and beans. These nodules contain nitrogen-fixing bacteria, such as Rhizobia. They take in nitrogen from the atmosphere and pass it on to the plant, allowing it to grow in soil low in nitrogen. As plants cannot absorb nitrogen directly from the air, these bacteria help in providing important nutrients to the plant. These bacteria live in symbiosis with the plants.

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Question:51

How do fossil fuels cause air pollution?
Answer:

Fossil fuels such as coal, oil, and natural gas are used to produce energy for various purposes like running vehicles, generating electricity, etc. However, burning fossil fuels releases harmful gases, which causes air pollution. Gases like carbon dioxide and sulphur dioxide are released that cause global warming and acid rain that damage the plants, soil, and water bodies.

1. Fossil fuel combustion also releases tiny particles known as particulate matter. These particles are so small that they enter into the lungs and cause health problems such as asthma.
2. Sulfur dioxide and nitrogen dioxide mix with water in the air to form acid rain that damages buildings and plants.
3. Carbon dioxide traps heat in the atmosphere, leading to climate change and weather.

Question:52

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

The major causes of water pollution are:

• Dumping of industrial waste, chemicals, and oils into rivers and oceans makes the water dirty.

• Household waste, detergents, and sewage get into the water and pollute it.

• Pesticides and fertilizers from farms get washed into rivers, which harms aquatic life.

• Plastic waste thrown into water bodies causes pollution and kills marine animals.

• Oil spills from ships pollute large areas of oceans, making the water toxic.

Measures we can take to reduce water pollution are:

• To reduce water pollution we can avoid throwing waste in water bodies.

• We can use eco-friendly products and limit the use of harmful chemicals.

• Reducing plastic use and properly disposing of waste prevents it from getting into the water sources.

• Supporting clean-up drives and spreading awareness can make a positive impact.

• Saving water and using it wisely reduces wastewater and pollution.

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?
Answer:

When a car is parked under the sun with all its windows closed, the inside temperature rises quickly due to the greenhouse effect. Sunlight enters the car through the glass and heats the surfaces. After that, these surfaces release the heat as infrared radiation, but the glass prevents this heat from going outside. As a result, the heat gets collected inside thus causing the temperature to increase much higher than the outside.

Question:54

Justify “Dust is a pollutant”?
Answer:

Dust is considered a pollutant because it causes harm to the environment, human health, and even animals when present in large amounts. Dust is made up of tiny particles of soil, dirt, sand, and other materials that can be carried away by the wind. Less dust is natural and does not cause any harm, but large amounts of dust in the air become dangerous and act as a pollutant.

Effects on Human Health: When people breathe too much dust, it causes serious health problems. The tiny dust particles enter the lungs and cause coughing, sneezing, and difficulty in breathing. For people who have asthma or other breathing problems, dust makes their condition worse. The exposure for the long time can lead to lung diseases.

Impact on Animals: Dust can irritate the eyes and lungs of animals. If animals eat food or drink water with dust, it also affects their health, causing diseases.

Environmental Impact: Dust can also harm the environment. When dust settles on plants, it blocks sunlight and reduces the amount of light that plants can use for photosynthesis. This affects the growth of crops, which can lead to lower production. Dust can also pollute water when it is present in rivers and lakes, thus making it harmful to use.

Question:55

Explain the role of the Sun in the formation of soil.
Answer:

Sun performs an important role in the formation of soil, which is explained below:

1. The Sun heats the surface of rocks during the day, which makes them expand, and at night, the rock cools down and contracts. This repeated cycle of expanding and contracting makes cracks in the rocks, which break down into smaller pieces.
2. The breaking of rocks into smaller pieces due to these changes is called physical weathering. After some time, these small pieces become part of the soil.
3. The Sun's heat increases the speed of the chemical reactions between minerals in the rocks and substances like water. These reactions change the rocks, making them softer and easier to break down.
4. Once rocks break down, wind, water, and microorganisms break them into tiny particles. These particles mix with organic matter, becoming fertile over some time.
5. Without the Sun, the process of breaking down of rocks and forming soil would take much longer time or may not occur.

Question:56

Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Answer:
We commonly think of pollutants as contaminants that make the environment dirty or impure. A vivid example is Sulphur dioxide, a by-product of industrial activity. High levels of Sulphur dioxide cause breathing problems. Too much causes acid rain. Sulphur dioxide has a direct effect on health and the environment. Carbon dioxide on the other hand is absorbed by the plants to prepare food by the process of photosynthesis by using water and sunlight. While preparing food, plants use carbon dioxide to make sugar and release oxygen, which is required by humans and animals for survival.

However, carbon dioxide is considered a pollutant when in the atmosphere its level increases and becomes high. Normally, the amount of carbon dioxide in the air is maintained by the carbon cycle, but human activities, such as burning fossil fuels (like coal, oil, and gas) and cutting down forests, release large amounts of carbon dioxide. This extra amount of carbon dioxide traps the heat of the earth’s atmosphere and leads to global warming. This global warming leads to problems like the melting of ice and rising sea levels. This is why carbon dioxide is considered a pollutant when its level increases; otherwise, it is safe.