NCERT Exemplar Solutions for Class 9 Science Chapter 14 Natural Resources
These Solutions are part of NCERT Exemplar Solutions for Class 9 Science . Here we have given NCERT Exemplar Solutions for Class 9 Science Chapter 14 Natural Resources
Rivers from land, add minerals to sea water. Discuss how.
Rivers are formed from springs, melting snow and rain water flowing over land as run off. While, passing through and over the rocks, the flowing water picks up minerals. These dissolved minerals are taken by rivers to sea and make them available to marine organisms.
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How can we prevent loss of top soil ?
Control of Soil Erosion: Soil erosion can be prevented by providing plant cover to soil. Roots of plants hold the soil firmly around them. They increase water percolation during rains and decrease runoff. Vegetation cover also reduces direct pounding of soil by rain drops. The various methods to control soil erosion are as follows :
- Vegetation Cover: Soil should not be left uncovered. Tree plantation should be undertaken where vegetation cover is poor or absent.
- Controlled Grazing: Grazing should be limited to certain seasons and for limited number of animals.
- Slope is divided into a number of flat fields for slowing down the flow of water.
- Contour Bunding: Small bunds are raised on the edges of fields to prevent loss of top soil through wind or water.
- Conservation Tillage: Instead of conventional tillage, reduced or no tillage can be practised. It prevents erosion.
- Wind Breaks: Wind erosion is reduced if rows of trees and shrubs are planted at right angles to the prevailing direction of wind.
How is the life of organisms living in water affected when water gets polluted ? (CCE 2012)
Water gets polluted from domestic wastes, fertilizers, pesticides (from fields) and industrial wastes.
- Fertilizers and domestic wastes cause eutrophication or excessive growth and increased organic loading. This, reduces oxygen available to aquatic animals,
- Domestic waste carries pathogens of a number of diseases. Some of them can cause diseases in aquatic animals as well,
- Pesticides and industrial wastes carry toxins that directly harm the aquatic organisms.
During summer, if you go near the lake, you feel relief from heat. Why ?
During day time, air over the land becomes heated up, rises upward and creates an area of low pressure. Lake water is not heated up so quickly. Evaporation of water from its surface also cools it up. Therefore, air over the surface of lake is cooler. It moves towards the land where low pressure exists. Therefore, during day dme a cool breeze flows from lake to the land nearby.
In coastal area, wind current moves from sea towards the land during day but during night it moves from land to the sea. Discuss the reason.
Air Movement in Coastal Areas: In coastal areas, there is a regular flow of cooler air from sea towards the land during the daytime. It is because during the daytime land gets heated faster than water. Reradiation from land heats the air above it. The hot air rises and creates an area of low pressure. Sea water is not heated so rapidly. Air above sea remains comparatively cool. It has a higher pressure as compared to air over land. Therefore, cooler air present over sea moves towards land where low pressure exists.
Following are a few organisms :
(c) Mango tree
Which among the above can grow on stones and also help in formation of soil ? Write the mode of their action for making soil.
Lichens and Mosses.
Weathering by Living Organisms:
Living Organisms are cause biological weathering. Lichens growing on rock surface are able to extract minerals from the same. This produces small crevices where a thin layer of soil builds up. Mosses grow over these crevices. They cause deepening of crevices and building up of more soil in them. Deeper crevices form cracks.
The cracks become bigger when the roots of short lived herbs pass into them. With the passage of time roots of bigger plants pass into cracks. Cracks widen and cause slow fragmentation and later pulverisation of rocks.
Soil formation is done by both abiotic and biotic factors. List the name of these factors by classifying them as abiotic and biotic.
Abiotic Factors : Sun, water, wind.
Biotic Factors : Lichens, mosses, herbs, shrubs and trees.
All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms ? Discuss.
Most of them first enter plants and become components of organic materials during the process of photosynthesis. They enter plants from air (CO2), water and ions (from soil). From plants the chemicals pass on to other organisms.
Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere ?
Through biogeochemical cycling where there is repeated circulation of biogenetic nutrients between abiotic and biotic components of the environment.
Why has moon very cold and very high 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 ? (CCE 2012)
Moon does not possess atomosphere. Atmosphere being a bad conductor acts as a temperature buffer on earth. This is not so on the moon. Therefore, moon gets heated up as the sun rays fall on its surface. It cools down drastically when there is no sunlight.
Why do people love to fly kites near the sea shore ? (CCE2012)
- There is a regular unidirectional wind from sea to land.
- It helps in flying the kite high.
- The wind is cooler and provides comfort even in bright sun.
Wliy does Mathura refinery pose problems to the Taj Mahal ? (CCE 2014)
Mathura refinery emits hydrocarbons and sulphur oxides. Hydrocarbons induce the formation of ozone which is highly oxidising. Sulphur dioxide produces acid rain which has a corroding effect on marble. Therefore, Mathura refinery does pose problems to Taj Mahal.
Why do not lichens occur in Delhi/Mumbai whereas they commonly grow in Manali/Ooty or Darjeeling ? (CCE 2011, 2012)
Lichens are sensitive to sulphur dioxide which occurs in sufficient quantity in the atmosphere of Delhi due to large number of
vehicles, homes and factories using fossil fuels. Moreover, Delhi occurs in semi-arid area where, atmospheric moisture is low. In Manali and Darjeeling, the atmosphere is humid and sulphur dioxide pollution is comparatively low.
Wliy does water need conservation even though large oceans surround the land masses ? (CCE 2012)
Marine water is unfit for consumption by humans, industries or land plants and animals. Therefore, terrestrial biota and human beings have to depend upon fresh water resources available on land (only about 0.5% of the total). The same has to be conserved.
There is a mass mortality of fish in a pond. What may be the reasons ?
- Passage of pesticide rich water from crop fields. ,
- Pouring of industrial waste. .
- Pouring of hot water from an industry or thermal power plant.
- Release of waste rich in heavy metal and mercury.
- Blockage of fish gills by some suspended pollutant.
- Excessive eutrophication.
Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil ?
Ans. Lichens release small quantity of acids which corrode the surface of rocks creating small pores and releasing minerals. With the passage of time the porous surface changes into thin layer of soil.
“Soil is formed by water”. If you agree with this statement, then give reasons.
Yes, “action of water in weathering” (wetting and drying, frost action, abrasion).
- Wetting and Drying. Certain rock components can pick up and lose moisture. They undergo swelling and contraction resulting in fragmentation of rocks.
- Frost Action. Water seeping in cracks would swell up and exert a great pressure if it freezes due to low temperature. The rock would undergo fragmentation.
- Running water carrying rock fragments would break and grind rocks occurring in the pathway. Rain and hail also cause rock breaking.
Fertile soil has lots of hurpus. Why ? (CCE 2012)
Fertile soils possess lots of humus because
- Humus is required for binding soil particles into crumbs. Crumb formation is needed for both hydration and aeration of soil,
- Humus makes the soil porous for easy passage of roots,
- It is source of minerals.
- Humus contains chemicals that promote growth of plants.
Why step farming is common in hills ?
Step farming or terracing is carried out in the hills because it slows down the speed of rain water currents, checks soil erosion and increases water absorption by soil.
Why are root nodules useful for the plants ? (CCE 2012)
Root nodules mostly occur in legume plants. These nodules contain nitrogen fixing bacteria named Rhizabium. The bacteria pick up nitrogen from soil atmosphere and convert it into organic compounds. The same pass into plant so that legumes become rich in proteins and other nitrogen compounds.
How do fossil fuels cause air pollution ? (CCE 2012)
Fossil fuels (coal, petroleum) are burnt to obtain energy.
- Suspended particles
- Sulphur oxides
- Nitrogen oxides
- Carbon monoxide
- Vapours of hydrocarbons.
All these are air pollutants. Hydrocarbons are a source of cancer. They also damage internal organs. Alongwith nitrogen oxides, they produce ozone and smog. Sulphur and nitrogen oxides give rise to acid rain. They are also irritants and damage eyes and nasal tract.
What are the causes of water pollution ? Discuss how you can contribute in reducing water pollution ?
Causes of Water Pollution:
- 21% of all infectious diseases and 66% of all deaths of children below 5 years are caused by contamination of drinking and bathing water by pathogens present in sewage, e.g., cholera, typhoid, diarrhoea, dysentery, jaundice, etc.
- Toxic Chemicals: Industrial effluents pass down a number of toxic chemicals, g., mercury by paper industry (minamata disease), cadmium (itai-itai disease), lead (plumbism), nitrate (met-haemoglobinaemia).
Reduction in Water Pollution :
- Sewage: The authorities can be prevailed upon not to pass untreated sewage into water bodies.
- Garbage: Domestic waste or garbage should not be thrown on the banks of water body.
- Industrial Effluents. Asking the industrial houses not to pass the untreated effluents into water body.
- Washing Clothes: Washing clothes should be discouraged on the banks of water bodies as detergents are a source of eutrophication.
- Vegetation: Plant trees, shrubs and herbs on the banks. This checks soil erosion and siltation of water bodies. It also reduces run off from fields.
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? (CCE 2012)
Glass is transparent to sunlight, allowing it to pass into the interior of the car. It heats up the interior. But heat waves do not escape from the car due to glass being opaque to the same. As a result, the interior of the car placed in the sun will become very hot. It is similar to glass house effect.
Justify “Dust is a pollutant.” (CCE 2012)
- Dust consists of suspended particles. The latter pass into nasal tract and cause a lot of discomfort including allergic asthma, bronchitis, cough and cold,
- Dust reduces light intensity,
- Its particles are eye irritants,
- Dust settles over plant foliage and reduces photosynthetic activity,
- Dust particles block stomata reducing gaseous exchange,
- Dust particles can pick up toxic metals and chemicals being emitted by industries.
Explain the role of the sun in the formation of soil.
Paedogenesis: It is the process of formation of soil from rocky crust of earth. Paedogenesis occurs in two stages, weathering and humification.
It is the process of breaking down of rock present on the surface of earth into fine particles. Weathering is caused by three types of processes — physical, chemical and biological. Physical weathering is pulverisation of rocky matter caused by physical phenomena like atmospheric changes (heating, cooling, wetting-drying, frost action) and mechanical forces (abrasion by rain and hail, rolling stones carried by water, wave action, sand blast by wind). Chemical weathering is pulverisation of rocks by chemical action in wet weather like hydration, oxidation, reduction, carbonation and solubilisation. Biological weathering is the breaking down of rocks by the action of living organisms.
Sun: It heats up the rocks during the day. Heating causes the rocks to expand. During night, the rocks cool and contract. Different parts of a rock expand and contract at different rates resulting in its cracking and breaking up into smaller pieces or fragments.
It is the addition of partially decomposed organic matter or humus to the weathered rock particles to form soil. Humus binds the finely ground rock particles into aggregates called crumbs. Crumb formation is needed for both hydration and aeration of soil.
Carbon dioxide is necessary for plants. Why do we consider it as a pollutant ? (CCE 2014)
Besides being essential for photosynthesis, carbon dioxide is a green house gas. Upto 350 ppm, it is both a good raw material as well as essential for keeping the earth warm. However, when its concentration rises (as presently it is 400 ppm), it becomes pollutant because it results in global warming. The latter is quite dangerous because it will melt polar ice, raise the water level of oceans and submerge several coastal areas and islands.
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