Dr PS Verma VK Aggarwal Class 9 Biology 6th Chapter Natural Resources Solution

Dr PS Verma Dr. VK Aggarwal Solution Class 9 Biology 6th Chapter – “Natural Resources” in here.

(1) The composition of air are: Nitrogen, Oxygen, Argon, Carbon dioxide, Miscellaneous.

(2) The Oxygen is inhale by all living organisms whereas exhale carbon di oxide as well Carbon Di Oxide is inhale by plants and exhale Oxygen, Thus remain remain constant these gas in the atmosphere.

(3) The atmosphere keeps the average temperature of the earth fairly steady during the day as the atmosphere prevents the sudden increase in temperature during the daylight hours and at night atmosphere slows down the escape of heat into the outer space.

(4) The movement of air is called Wind. THE movement of air from one region to the other creates winds.

(5) (i) Take 3 vessels.

(ii) 1st beaker full of water, 2nd beaker full of soil and a 3rd containing a thermometer.

(ii) Keep them in bright sunlight for 3 hours.

(iii) Now, measure the temperature of all three vessels and also take the temperature reading in shade at the same time.

(iv) It will be seen that the temperature of the soil and sand is more than that of water in bright sunlight because sand and soil gets heated by solar radiations faster than the water.

(v) Therefore, land would become hot faster than the sea.

(vi) It will also observe that the temperature of air in shade is different from the temperature of soil, sand and water in bright sunlight because of the direct effect of radiations.

(6) When the sunlight fall on the earth, some are absorbed and majority of these are reflected back or re-radiated by the land and water bodies. These reflected or re-radiated solar radiations heat the atmosphere from below. As a result convection currents are set up in the air.

(7) The factors that influence movement of air are following:

(i) Uneven heating of land at different parts of the earth.

(ii) Differences in heating and cooling of land and water bodies.

(iii) Vapourisation and condensation of water vapours.

(iv) Rotation of earth.

(v) Presence of high mountain ranges in the paths of wind.

(vi) Difference in topography over which the wind passes. (8) An enormous collection of tiny droplets of water appear in the form of clouds. These droplets o9f water once formed slowly grow bigger due to condensation of more water droplets. When the droplets become big and heavy they fall down in the form of rain.


->Take an empty plastic bottle.
->Pour 5 to 10 ml water into it and close the bottle tightly with a cap.
->Shake the bottle well and then place it in the sun for about ten minutes.
->Now, open the cap of the bottle and allow some smoke from the lighted incense stick to enter the bottle.
->Quickly close the bottle tightly with the cap.
->Press the bottle hard between your hands as much as possible.
->After few seconds release the bottle. Press the bottle again as hard as you can.

This simple experiment replicates, on a very small scale, the happenings when air with a very high content of water vapour goes from a region of high pressure to a region of low pressure. When bottle containing water is kept in the sun, the water evaporates and air inside the bottle gets saturated with water vapour. When the bottle is pressed between your hands, the pressure inside becomes high and air inside the bottle moves in a region of low pressure. It expands and cools. The smoke particles act as ‘nuclei’ on which water vapours condense in the form of tiny droplets. When you release the pressure, the air inside the bottle becomes foggy. When bottle is again pressed, the fog will disappear. It is so because due to high pressure condensed water vapours will fall down and collect as water at the bottom of the bottle. When the experiment is repeated without smoke inside the bottle, one will not observe foggy air inside the bottle as smoke particles are absent and nothing is available in air to act as ‘nucleus’ for water vapours to condense as tiny droplets.

(10) The major components of air pollution are pointed below:

(i) Forest fire, dust storm, pollen causes air pollution.

(ii) Burning of fossils fuels in Industries, vehicles and thermo electric plants, gaseous emission from industries, minining , processing, stone crushing causes air pollution.

(11) Many injurious effects such as falling of leaves, reduced growth, degeneration of chlorophyll, mottling of leaves etc have been noticed in plants. Lichens are very sensitive to the levels of contaminants such as sulphur di oxide present in polluted air. Further Sulphur reacts with water in the atmosphere to form sulphuric acid. This sulphuric acid is washed down into the soil by rain named as Acid Rain.

(12) Smog: Smog is a photochemical haze caused by the action of solar ultra violet radiation on atmosphere polluted with primary pollutants such as hydrocarbons and oxides of nitrogen from automobile exhaust.


It reduces visibility and is highly suffocating and toxic to humans, animals and plant.

(13) Effects of Air Pollution on Human beings are followed:

(i) SPM causes asthma, Bronchitis and allergic cold.

(ii) Pollutant gases cause irritation in eyes, throat and lungs. They injure lungs, liver, kidneys, spleen and nervous system.

(iii) Hydro carbon vapours not only damage the internal organs but also cause cancer.

(14) Air movement in coastal areas:

In coastal areas , during day time there is regular flow of cool air from the sea towards the land.

At night there is a reverse flow of air from land to sea.

(15) Role of Atmosphere in Climatic Control:

Air is an inexhaustible natural resources. Without air in the world is harmful. This is because All the things in the world directly or indirectly depends on air. Air is a bad conductor of heat. The atmosphere keeps the average temperature of the earth fairly steady during the day as the atmosphere prevents the sudden increase in temperature during the daylight hours and at night atmosphere slows down the escape of heat into the outer space.

(16) Atmosphere is devided into five distinct layers of zones.

(i) Troposphere: It is the lowest region of atmosphere which contains air and subject of differential heating. It extends surface of earth upto 8 to 20 km.

(ii) Stratosphere: It is the second region after troposphere. It extends from 20-50 km.

(iii) Mesosphere: After Stratosphere the mesosphere is come. It extends from 50 – 100 km.

(iv) Thermosphere: Above the mesosphere the thermosphere extends up to near 375 miles (600 km) above the earth. This layer is known as the upper atmosphere. As such, incoming high energy ultraviolet and x-ray radiation from the sun, absorbed by the molecules in this layer, causes a large temperature increase.

(v) Exosphere: The highest region of the atmosphere exist above the thermosphere.

(17) Natural sources of Air pollution: Forest fir, dust storm and pollen are the natural sources of air pollution.

Human Sources of Air Pollution: Burning of fossils n Industries, vehicles and thermo electric plants, gaseous emission from industries, minining , processing, stone crushing causes soil pollution.

(18) When water bodies get heated by solar radiation during the day a large amount of water evaporates and goes into the air. The air carrying water vapour also get heated . This hot air rises up, carrying water vapour with it. As the air rises it expands and cools.

This cooling causes the water vapor in the air to condense in the form of tiny droplets. Such process of condensation of water is facilitated when dust and other suspended particles act as the nucleus for these droplets form around.

An enormous collection of tiny droplets of water formed clouds.

(19) The increase in carbon-di-oxide in the atmosphere intensifies the greenhouse effect and leads to global warming.

Effect of Global Warming:

It increase the average temperature of the earth.

(20) Reduction in the concentration of ozone layer is called ozone depletion. It is caused by certain chemicals called ozone depleting substances. The important ozone depleting substances are CFC, Halons, Mythyl bromide, nitrogen oxides and chlorine.

Effects of Ozone depletion:

(i) Skin cancer.

(ii) Damage of eyes also increase in incidence of cataract disease in eyes.

(iii) Damage of Immune system.

(21) Acid rain wash down into the soil and make it highly acidic, thus, affecting the growth of plants and ultimately the forest growth. It also affects the surface of buildings by eroding the stone and brick works.

(22) The technique which is used to capture, store and reutilise rain water by making special water harvesting structures such as dug out wells, percolation pits, check dams and lagoons.

Rain water harvesting is beneficial for all particularly in the region of scanty rainfall.

(23) The weather conditions (including temperature, humidity, atmospheric pressure, wind, and precipitation.) prevailing in an area in general or over a long period called climate.

(24) Every moments there are changes in the temperature, biometric pressure, humidity, precipitation, sunshine, cloudness, wind direction, speed, and other conditions in the troposphere. These short term changes in the properties of the troposphere form the weather.

(25) CFC’s are chlorofluoro carbons which deplete the ozone layer.  The effects of chlorofluoro carbons:

(i) Skin cancer.

(ii) Damage of eyes.

(iii) Damage of immune system.

(iv) Decreased crop yields.

(26) Soil is formed by the breakdown of bigger into smaller mineral particles is called weathering.

The various type of weathering are following:

(i) Physical weathering: Various climatic factors such as temperature, wind, rain water, ice snow, glaciers and running water contribute to physical weathering.

(ii) Chemical weathering: It involves a variety of chemical processes such as hydrolysis, hydration, oxidation and reduction. The breakdown of complex compounds by the carbonic acids present in water and acidic substances derived from the decomposition of organic matter in soil, are examples of chemical weathering.

(iii) Biological weathering: This is done by living organisms Ex. Lichens and mosses.

(27) The removal and transportation of the top layer of soil from its original to another place under the effect of strong winds and fast running rainwater is called soil erosion.

Some of meaning of prevention are pointed below:

(i) If the fields remain covered with crops throughout the year, their top soil will not be exposed to winds or rains. In such a condition no soil erosion will occur.

(ii) In terracing the sloped are divided in to a number of flat fields to slow down the flow of water.

(iii) small bunds are raised on the edges of fields to prevent loss of top soil through wind or water.

(28) Organisms contribute in the formation of soil: Biological weathering is done by living organisms such as lichens and bryophytes. Lichens growing on rock surface extract minerals from the rocks. This creates small crevices at places where a thin layer of soil builds up. Mosses grow over these crevices causing deepening of crevices and results in the buildup of more soil inside them. The roots of short lived herbs also passes into them and the cracks gradually widen and cause slow fragmentation and eventually pulverisation of rocks.

(29) Water is replenished in the seas by the means of water or hydrological cycle. We know that the oceans or seas are the largest global reservoir of water. Water evaporates from these reservoirs in large quantities and helps in the formation of clouds.

The winds blows the clouds over to the lands where after getting cooled enough, the water in clouds falls on the earth or directly over the seas as rain and hail. Some water from rain and melting snow soaks into the ground, but most of it flows in rivers and returns directly to the seas.

(30) The process of biofixation of nitrogen is called nitrogen fixation.

(31) During lightning nitrogen of atmosphere reacts with oxygen to form dilute nitric acid. This acid comes down to earth with rainwater.

(32) Carbon replenishment of Atmosphere: The carbon cycle is linked to energy flow because producers – including photosynthetic plants of the forests and oceans and chemosynthetic bacteria of deep sea vents require environmental energy to trap carbon into sugars. The trapped carbon comes from carbon di oxide in the surrounding air or water.

As the cycle proceeds, consumer devour the organic compounds that producers manufacture. Then via respiration both consumers and producers return carbon to the monliving environment in the form of carbon di oxide.

(33) One of the danger of continued global warming is methane burp which is caused by the melting of the methane hydrates in permafrost and on sea floor. Methene being a green house gas increases global warming.

(34) Carbon dioxide concentration in atmosphere is rising primarily because of two reasons:

(i) Deforestation

(ii) Increased combustion of fossil fuels.

As trees inhale Carbon Di Oxide and exhale Oxygen by plants into the air, in the other hand this oxygen is inhale by human beings and olther creatures, so it maintain a balance. But due to deforestation Carbon di oxide is increased rapidly.

The increased combustion of fossil fuels also leads to the release of enormous amounts of carbon dioxide in the atmosphere.

(35) The part of atmosphere which is rich in ozone called Ozone umbrella. The ozone layer is highly important as it filters out the harmful, high energy ultraviolet radiations coming from sun. The high energy ultraviolet radiations split into molecular and atomic oxygen.

(36) The effects on widening of ozone hole-

(i) Skin cancer.

(ii) Damage of eyes.

(iii) Damage of immune system.

(iv) Decreased crop yields.

(37) Water is one of the most important physical components which is essential for the survival of live on earth. Ocean is the biggest storehouse of water. Water on evaporation forms clouds and which after condensation falls down as rain. After rain, it passes through rivers and gets collected again in the ocean. The circulation of water in this manner is called water cycle.

The cycle is also performed through living beings in the processes like absorption and transpiration of water by plants and drinking by animals. Animals lose water during respiration and evaporation, excretion etc.

(38) Check the book.

(39) The four type of bacteria are: Nitrogen-fixing bacteria, e.g. Rhizobium, Ammonifying bacteria, Nitrifying bacteria, e.g. Nitrosomonas, Nitrobacter, and Denitrifying bacteria.

(40) Check the Book for Oxygen cycle in nature.

(41) Check the Book for Hydrological cycle in nature.

(42) Three aspects of nutrient cycles:

(i) Input of nutrients: An ecosystem receives the nutrients from an external source. It stores them for further use through biological processes.

(ii) Output of nutrients: Nutrients move out of an ecosystem and many of them become input to another ecosystem.

(iii) Internal nutrient cycling: Nutrients are continuously regenerated and stored in soil in forms available to plants. This is done by decomposers by the process of decomposition of detritus.

(43) Biological Water Cycle: The organisms get water from and return it to the global water cycle. Plants absorb water from the soil or water reservoir and add it to the air in vapour form by a process called transpiration.

Water transpired by trees cools the surrounding air.

Animals take water from the water reservoir or with food and return it to the air and vapours by respiration or to the soil by excretion.

Mammals also excrete water as sweat which evaporates from the water bodies. Water is added to the environment by the death and decay of organisms. Water vapour formed by transpiration and respiration form clouds and enters global water cycle.

Rain adds water to the soil and reservoir for reuse by plants and animals. This way completes water cycle.

Long Answer Type Questions: (Carrying 5 marks each) Page No. 367

(1) Natural resources are living and non living components of nature which are used by humans to meet their requirements. Since natural resources are available only from the earth, they are called earth resources.

Natural resources are of two types: Inexhaustible and Exhaustible.

Inexhaustible Resources: They are natural resources which occur in such abundance that they are not likely to get exhausted despite continuous use. Ex. Air, Water, Solar energy.

Exhaustible Resources: They are natural resources which are available in limited quantity. Exhaustible resources  are of 2 kinds.

(a) Renewable resources: Ex. Forest, Wild life, soil and under ground water.

(b) Non- Renewable resources: Minerals, Fossils fuels (Coal, Petroleum).

(2) This is because without air life is impossible. Air is needed for every living things including human body , birds, animals, insects every things.

Function of Air:

Air is an inexhaustible natural resource. In a world without air, there would be no plant or animal life, no winds, clouds or rain, no fires and no protection against harmful solar radiations. This is because the atmosphere covers the Earth, like a blanket. Air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of whole year. The atmosphere prevents the sudden increase in temperature during the daylight hours. And at night, atmosphere slows down the escape of heat into outer space.

(3) Causes of Air Pollution:

(i) Forest fire, dust storm, pollen causes air pollution.

(ii) Burning of fossils fuels in Industries, vehicles and thermo electric plants, gaseous emission from industries, minining , processing, stone crushing causes air pollution.

Effects of Air Pollution :

(i) SPM causes asthma, bronchitis and allergic cold.

(ii) Pollutant gases cause irritation in eyes, throat and lungs.

(iii) Hydrocarbon vapours not only damage the internal organs, but also cause cancer.

(4) Reduction in the concentration of ozone layer is called ozone depletion. It is caused by certain chemicals caused ozone depleting substances. ^The important ODS are chloroflurocarbons (CFCs), halons, mythyl bromide, nitrogen oxides and chlorine, CHCs such as carbon tetrachloride, dichlorodifluoromethene. They are rich in chlorine, fluorine and carbon. CHCs are commonly used as aerosol propellants, refrigerants, shaving foams, spray agent in scents etc.

Effects of Ozone depletion:

(i) Skin cancer.

(ii) Damage of eyes.

(iii) Damage of immune system.

(iv) Decreased crop yields.

(5) Various Sources of Water Pollution:

(i) Organic wastes are contributed as domestic and commercial sewage by food processing plants, dairy farms, piggeries, poultry farms, slaughter houses, breweries, tanneries, etc. Animal excreta is discharged into fields or dumped into pits reaches water bodies through run off and leaching, particularly during the rainy season.

(ii) The industrial wastes (including washing machinery, products) causes water pollution.

(iii) Water containing detergent, soaf discharging causes water pollution.

(iv) For getting higher crops, fertilizer is used rapidly in the field. In rainy season These are washed away and poured in ponds, lake other water bodies and pollute them.

(v) Rain erodes soil and carries silt to water. Tiny suspended particles of clay and dust also settle in water from air. These soil particles cause turbidity.

Effects of Water Pollution:

(i) Pathogens are biological pollutants of water. They include viruses, bacteria, fungi, protozoan, nematodes etc., They cause following disease such as typhoid, cholera, dysentery, jaundice and hepatitis.

(ii) The pollutants can encourage the growth of some life forms and can harm some other life forms.

(iii) With increase in the amount of organic wastes in water, bacteria multiply rapidly and use up the available oxygen. Lack of oxygen kills the fish and other animals.

(6) Eutrophication:  Eutrophication is nutrient enrichment of water body that results in the growth of aquatic plants, especially algae causing colouration of water known as algal bloom. It leads to depletion of dissolved oxygen in water resulting in killing of aquatic organisms Ex. Fish.

Biomagnification: The phenomenon of increase in the concentration of harmful non-biodegradable substances in the body of living organisms at each trophic level of the food chain is called biomagnification. Ex. mercury and cadmium.

(7) Human body needs water to survive. Our body is made up of cells and I order for cells to perform normally they need water. Cells perform all its functions in the presence of water.

In human body, water is a medium for almost every cellular function.

Not just human beings plants, animals, microbes all need water to survive.

(8) Soil: Soil is the portion of the earth surface that consists disintegrated rock and decaying organic material. It provides support for many plants and animals.

Thickness of soil on the earth’s surface ranges from a few millimeters to 3 – 4 meters. Terrestrial and Aquatic plants depend upon the soil and water bed, respectively for their nutrients, water supply and anchorage.

Formation of Soil:

In two way soil is basically formed.

(i) Weathering

Break down of bigger rocks into smaller mineral particles is called weathering.

(ii) Peadogenesis

This process concludes the decomposition by bacteria, fungi during which organic materials are broken down leading to humification and mineralization.

(9) Human activities are the primary cause of soil pollution and land degradation.

Rich use of chemicals and pesticides for well cropping causes soil pollution.

The industrialized waste thrown away, which are causes soil pollution.

Throwing of plastics here and there causes soil pollution.

Effects of Soil Pollution:

Use of these substances over long period of time can destroy the soil structure by killing the soil microorganisms that recycle nutrients in the soil. It also kills the earthworms which are helpful in making the rich humus. Fertile soils can quickly become barren if sustainable practices are not followed.

(10) The removal of top soil from its original place to another place is called soil erosion.

Causes of Soil Pollution:

(i) Strong winds causes soil erosion.

(ii) Heavy rains causes soil erosion.

(iii) Deforestation is another reason of soil erosion.

(iv) Dust storms shift huge amounts of loose soil from one place to another causes soil erosion.

(v) Frequenly flooding of rivers is another cause of soil erosion.

Effects of Soil Erosion: The various effects of Soil Erosion are followed-

(i) Loss of fertility and desertification.

(ii) Landslides in hilly areas causes soil erosion.

(iii) Top soil, when washed down by water, clogs drains, water channels etc, due to deposiotion. Silt pollutes the water. Problem of silting in water reservoirs lowers the water level in them which ultimately leads to shortage of production by the hydroelectric power stations.

Prevent of Soil Erosion: The various prevention on the tropic of Prevention of Soil Erosion point out one by one below,

(i) Intensive cropping.

(ii) Sowing grasses and planting xerophytes.

(iii) Terrace farming.

(iv) Contour bunding etc.

(11) Nitrogen cycle : Continuous process by which nitrogen is exchanged between organisms and the environment is called nitrogen cycle. Nitrogen is an essential nutrient, needed to make amino acids and other important organic compounds, but most organisms cannot use free nitrogen, which is abundant as a gas in the atmosphere.

Nitrogen cycle involves the following steps:

(i) Nitrogen fixation: This process involves the conversion of atmospheric nitrogen into nitrates, which are soluble in water. This is done by various nitrogen fixing bacteria. Example – Rhizobium, blue green algae and bacterium Azotobacter.

(ii) Ammonification: It is the process of decomposing complex, dead organic matter into ammonia. This is done by microorganisms living in the soil.

(iii) Nitrification: It is the process of conversion of ammonia into nitrites and then into nitrates. This is done by nitrifying bacteria. Example – Nitrosomonas and Nitrobacter.

(iv) Denitrification: It is the process of reducing nitrates present in the soil to release nitrogen back into the atmosphere. Example – Pseudomonas.

(12) The decomposers help in decomposing the dead bodies of plants and animals and hence act as important role of environment.

The decomposers also help in putting back the various elements of which the dead plants and animals were made, back into the soil, air and water for reuse by the producers like crop-plants.

Decomposer ensure the eco balance of the nature.

They decompose the waste therefore prevents bad smell of rodden things.

They also enrich the growth of plants.


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