Science Ncert Exemplar 2019 Solutions for Class 9 Science Chapter 14 - Natural Resources

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Land and water bodies absorb some of the solar radiations falling on earth and reflect back most of the radiations to atmosphere. This results in heating up of the atmosphere.

Hence, the correct answer is option (d).

Answer:

The atmosphere keeps the average temperature of the Earth fairly steady. As we know that air is a bad conductor of heat, the atmosphere prevents the sudden increase in temperature during the daytime. And during the night, it slows down the escape of heat into outer space. Therefore, the temperature does not drop to freezingly low levels.

Hence, the correct answer is option (c).

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Ozone is helpful in preventing harmful ultraviolet (UV) rays from reaching the earth but only when, present in an appropriate amount. Excess of ozone is harmful and living forms require oxygen to respire. If all the oxygen is converted to ozone, then, these living forms would die.

Hence, the correct answer is option (b).

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Sun, water, wind and some living organisms play an important role in soil formation. But polythene bags contaminate the soil and degrade its fertility.

Hence, the correct answer is option (d).

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Oxygen is present in the atmosphere in two forms, namely, diatomic oxygen (O₂) and triatomic ozone (O₃).

Hence, the correct answer is option (c).

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The nitrogen-fixing bacteria are anaerobic i.e. survive in absence of elemental oxygen.

Hence, the correct answer is option (b).

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Water evaporates from the water bodies and subsequent condensation of this water vapour leads to rain. So, rainfall patterns depend on the recycling of water vapours, which, in turn, are dependent on the number of water bodies in an area.

Hence, the correct answer is option (b).

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The use of large amount of fertilisers and pesticides leads to soil pollution. Their excess is harmful to the environment and they are not eco-friendly.

Hence, the correct answer is option (a).

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The nitrogen molecules in the air are converted to nitrates and nitrites by the nitrogen-fixing bacteria which are found in the roots of legumes (generally the plants which give us pulses) in special structures called root nodules.

Hence, the correct answer is option (a).

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Photosynthesis is a part of the carbon cycle, not the water cycle. Water molecules are consumed in photosynthesis along with carbon dioxide in the presence of sunlight and chlorophyll to produce glucose molecules.

Hence, the correct answer is option (d).

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A change in pressure of the water bodies is due to physical causes and can not be termed as water pollution.

Hence, the correct answer is option (c).

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Green house gases prevent the escape of heat from the Earth and an increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase worldwide. Examples include carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, carbon monoxide, etc. But ammonia is not a green house gas.

Hence, the correct answer is option (d).

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Transpiration is the loss of water molecules from plant leaves. It is a part of water-cycle, not carbon-cycle.

Hence, the correct answer is option (b).

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Ozone-hole means a reduction in the ozone layer due to the reaction of chlorofluorocarbons with ozone molecules. It was first discovered over Antarctica.

Hence, the correct answer is option (b).

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Excessive use of man-made compounds like chlorofluorocarbons (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) has resulted in a reduction of the ozone layer. They are found to persist in the atmosphere and react with the ozone molecules to convert them into oxygen molecules.

Hence, the correct answer is option (c).

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Increased use of chlorofluorocarbons has depleted ozone layer. Also, the burning of fossil fuels has increased the percentage of green house gases in the atmosphere leading to green house effect and eventually, raising the temperature of the earth. All these problems have developed recently.

Hence, the correct answer is option (d).

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Nitrogen is an inert gas abundant in the atmosphere. It is not used by our body in elemental form and exhaled out as such along with CO₂.

Hence, the correct answer is option (b).

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The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil. The quality of the topsoil is an important factor that decides biodiversity in that area.

Hence, the correct answer is option (d).

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Carbon is found in the combined state as carbon dioxide in the atmosphere. Through the process of photosynthesis in plants, carbon dioxide from the atmosphere is converted into glucose molecules (organic carbon in plants). When animals consume plants, these glucose molecules are used to release carbon dioxide and give energy (organic carbon in animals). When plants and animals die, they get decomposed into inorganic carbon in the soil.

Hence, the correct answer is option (b).

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Soil is formed by the breaking down of rocks over millions of years by various physical, chemical, and biological processes. The mineral nutrients that are found in a particular soil depend on the rocks it was formed from.

Hence, the correct answer is option (a).

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Water covers 75% of the Earth’s surface.

Hence, the correct answer is option (a).

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Living things constitute the biotic component of the biosphere. The air, the water and the soil form the non-living or abiotic component of the biosphere.

Hence, the correct answer is option (d).

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Desert plants need oxygen, water, and minerals for abundant growth. An increase in carbon dioxide content in the atmosphere would not help them grow.

Hence, the correct answer is option (d).

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Photosynthesis is the process of taking up carbon dioxide from the atmosphere in the presence of sunlight and chlorophyll and giving glucose as the main product and oxygen as a side-product is released into the atmosphere.

Hence, the correct answer is option (c).

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The combustion of fossil fuels increases the amount of suspended particles (unburnt carbon particles or hydrocarbons) in the air. These suspended particles combine with fog during cold weather to form smog and lower the visibility.

Hence, the correct answer is option (b).

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While growing, lichens release certain substances that cause the rock surface to powder down and form a thin layer of soil. Other small plants like moss, are able to grow on this surface now and they cause the rock to break up further.

Hence, the correct answer is option (a).

Answer:

Aquatic organisms are used to a certain range of temperature in the water-body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding. The eggs and larvae of various animals are particularly susceptible to temperature changes.

Hence, the correct answer is option (a).

Answer:

Soil erosion is the removal of fine particles of soil by flowing water or wind. The roots of plants have an important role in preventing soil erosion as they hold the soil tightly. So, forest cover needs to be increased in order to prevent soil erosion.

Hence, the correct answer is option (a).

Answer:

Roots hold up the soil tightly to prevent soil erosion. Vegetative cover on the ground has a role to play in the percolation of water into the deeper layers too. But when rain water falls on a soil without vegetative cover, topsoil is removed quickly.
Hence, the correct answer is option (b).

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Nitrogen fixing bacteria are anaerobic i.e. survive in absence of oxygen. Exposure to oxygen would kill them.
Hence, the correct answer is option (b).

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Water has the ability to dissolve a large number of substances. Some of the soluble minerals get dissolved in the water as water flows over the rocks constituting them. In this way, rivers from land, add minerals to sea water.

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Loss of top soil can be prevented by

• Making sure that deforestation levels do not disturb the ecological balance.
• Increasing the amount of vegetational cover for percolation of water into deeper layers.
• Controlling overgrazing by animals.

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When undesirable chemicals such as fertilizers, pesticides, domestic garbage and industrial waste are added to water bodies, they harm the aquatic life and cause diseases to the aquatic organisms. Besides, the demand of oxygen by aquatic organisms is also increased. There is a drop in the dissolved oxygen level in water which adversely affects the aquatic organisms. An abrupt temperature change of water bodies would be disastrous for aquatic organism residing in them or affect their breeding.

Answer:

Water bodies are warmer during the day. This leads to evaporation of water from them. As a result of evaporation, air near the lake is cooled and we get relief from heat.

Answer:

During the day, air above the land gets heated quickly and starts rising. This creates a region of low pressure and air over the sea rushes from high pressure region to this low pressure region. This movement of air is known as wind current. During night, air above the sea is warmer than the air on land because water cools down slowly. So, air moves from land to sea creating wind current in opposite direction.

Answer:

Lichens and mosses can grow on stones and also help in the formation of soil.
While growing on rocks, lichens release certain chemical substances that powder down the rocky surfaces and form a thin layer of soil. Now, small plants like moss, are able to grow on this surface and they cause the rock break up further.

Answer:

Abiotic factors— sun, water and wind
Biotic factors— lichens, mosses, tress, microorganisms and insects.

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C, N, S, P, H and O are essential components of biomolecules which are present in living organisms. Carbon (C) comes through photosynthesis and nitrogen (N) is obtained through nitrogen-fixing bacteria. Sulphur (S) and Phosphorus (P) are absorbed from the soil. Hydrogen (H) and oxygen (O) are obtained by water. Living forms also take up oxygen through inhalation of air. These nutrients are obtained by animals when they take food either directly or indirectly from plants.

Answer:

The percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere due to their continuous recycling in various biogeochemical cycles. These gases are taken up by human beings for their growth and development. But these are returned to the environment in one or another form, thereby, maintaining their constant composition.

Answer:

The atmosphere maintains the average temperature of the Earth fairly steady during the day and also throughout the year. Moon does not have an atmosphere. So, there is no way to prevent the sudden increase in temperature during the day on its surface. Also, during the night, lack of atmosphere can not slow down the escape of heat into outer space. Therefore, the temperature becomes very low i.e. –190°C at night and very high i.e. 110°C during day.

Answer:

The air above the land gets heated faster in coastal areas during the day and starts rising. Thus, an area of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one area to the other creates winds which are ideal for kite flying. Hence, people enjoy flying kites near the seashore.

Answer:

Mathura refinery releases toxic gases (like oxides of sulphur) which on combining with water vapours in atmosphere leads to formation of sulphuric acid. As a result, rainwater gets acidified and this causes acid rain. And, acid rain on reacting with calcium carbonate (marble) leads to corrosion of the marbles of Taj Mahal.

Answer:

Lichens are bio-indicators and sensitive to SOâ‚‚ pollution from automobiles. Delhi has a highly polluted environment due to large number of vehicles and therefore, does not support growth of lichens. However, Manali or Darjeeling has cleaner environment due to very less number of vehicles. So, lichens commonly grow in these cities.

Answer:

Most of the water present on the surface of Earth’s is found in seas and oceans and is saline. Terrestrial organisms require freshwater because their bodies cannot tolerate the high amounts of dissolved salts in saline water. Freshwater is found frozen in glaciers and on snow covered mountains. Most places face a shortage of water every summer. Due to the unequal distribution of limited freshwater resources, we need to conserve water to meet the demands.

Answer:

The reasons for mass mortality of fishes in a pond may be

• Respiratory organs (gills) could be blocked by any hazardous pollutant.
• Sudden increase in temperature of the pond.
• Addition of toxic chemicals like mercury in water.

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Lichens are called pioneer colonisers of bare rock as they are the first organisms to grow on rocks. While growing, they release certain chemical substances that cause the powdering down of rocks and form a thin layer of soil. Small plants such as moss can now grow on this surface and they further break down the rock.

Answer:

Yes, water helps in the formation of soil in following ways:
 

• Water causes different rocks to rub against each other, thus, creating small fragments which are taken downstream by water flow and deposited as soil. 
• It is also responsible for weathering down of rocks over prolonged period of time.
• Another way in which water cracks rocks into smaller fragments is by expansion on freezing in crevices of rocks.

Answer:

Fertile soil has abundant microorganisms that decompose dead organic matter to form humus. The quality of the soil is determined by the amount of humus and the microorganisms found in it. Humus is a major constituent of fertile soil because it provides the soil with all the essential nutrients and makes the soil more porous which enables air and water to penetrate deep under the ground.

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Steep slopes are common in hilly areas. So, there is a high risk of topmost layer of soil being lost by surface runoff down the slopes. Therefore, step farming is practiced in hills to prevent soil erosion through water streams on the slopes.

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Root-nodules are special structures found in the roots of leguminous plants, such as pulses, grams, etc. They are a home to very important nitrogen-fixing bacteria-rhizobium. These bacteria convert the atmospheric inert nitrogen molecule into soluble forms like nitrates and nitrites which can be taken up by plants from soil for further utilisation. Hence, root-nodules act provide shelter to essential bacteria which increase the soil fertility by the process of biological nitrogen fixation.

Answer:

The burning of fossil fuels like coal and petroleum produces different oxides of nitrogen and sulphur because these fuels contain small amounts of nitrogen and sulphur. Air pollution is the increase in the content of these harmful substances in air. Burning of fossil fuels cause air pollution in the following ways:

• Different oxides of nitrogen and sulphur dissolve in rain giving rise to acid rain.
• The regular inhalation of polluted air increases the risk of asthma, allergies, heart and cancer diseases.
• Release of greenhouse gases like carbon dioxide, methane, etc. into the atmosphere which leads to global warming.
• They enhance the amount of suspended particles (unburnt carbon particles called hydrocarbons) in air and lower the visibility, especially in cold weather. This is known as smog and is a visible indication of air pollution.

Answer:

Water pollution can be caused by addition of 

• Domestic sewage.
• Hot water from the power plant that increases the temperature and reduces the dissolved oxygen in water and hence, disturbing aquatic life.
• Toxic heavy metals like mercury, lead, etc.
• Radioactive substances and industrial effluents.
• Chemicals such as fertilizers and pesticides in water bodies. 

• We should avoid washing clothes near a water body because it adds lot of detergents to it which is harmful for aquatic life.
• The addition of toxic heavy metals like mercury, lead, chromium, etc. from industries should be prevented.
• Vegetational cover near river banks should be increased to check soil erosion.
• The water from sewer lines should be treated before discharging it into the water body.
• We should not dump our domestic waste in the water body.

Answer:

• The temperature inside the car rises very high due to greenhouse effect. Greenhouse effect is the heating up of Earth's surface due to trapping of incoming radiations from the sun by greenhouse gases like carbon dioxide.
• Infra-red radiations in sunlight pass through the glass and heat the interior of the car.
• The radiation emitted by 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 a smaller wavelength than that emitted by the interior of the car which is of a longer wavelength to which the glass is opaque.

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Any substance whose concentration increases beyond normal and degrades quality of air is termed as pollutant. Dust is considered as particulate air pollutant because

• Dust remains present in air as suspended particles and can cause allergy and other respiratory diseases.
• It also affects plant growth by covering stomata on leaf surface.
• It acts as a carrier of toxic compounds like heavy metals.
• It reduces the intensity of light by accumulating in upper layers of atmosphere to form large coloured clouds.
• It is an eye irritant.

Answer:

The rocks expand during the day due to heating up by the Sun. At night, these rocks cool down and contract. Since the whole mass of the rock do not expand and contract at the same rate, this leads to the formation of cracks and as a result, huge rocks break up into smaller fragments. This process continues over millions of years. The end result of this weathering down of rocks is the fine particles of soil.

Answer:

It is true that carbon dioxide is necessary for plants to carry out the process of photosynthesis in which glucose molecules are formed in the presence of sunlight and chlorophyll. But an increasing concentration of carbon dioxide is hazardous and considered as a pollutant. The burning of fossil fuels which provide energy for cooking, industrial processes and transportation have doubled up the percentage of carbon dioxide in the atmosphere. Carbon dioxide is one of the greenhouse gases. Higher concentrations of carbon dioxide would cause more heat to be trapped by the atmosphere and lead to global warming.