NCERT Exemplar - Natural Resources Class 9 Notes | EduRev

Science Class 9

Created by: Dr Manju Sen

Class 9 : NCERT Exemplar - Natural Resources Class 9 Notes | EduRev

The document NCERT Exemplar - Natural Resources Class 9 Notes | EduRev is a part of the Class 9 Course Science Class 9.
All you need of Class 9 at this link: Class 9

SHORT ANSWER TYPE QUESTIONS

Q.1. Rivers from land, add minerals to sea water. Discuss how?
Ans: As the river water flows from land, it passes over the rocks. It picks up minerals which get dissolved in the water. Minerals are then carried by the rivers to seawater.

Q.2. How can we prevent the loss of topsoil?
Ans: Loss of top soil can be prevented by:
(a) checking deforestation.
(b) preventing excessive grazing by animals.
(c) increasing the vegetational cover.

Q.3. How is the life of organisms living in water affected when water gets polluted?
Ans: The life of organisms living in water is affected when water gets polluted in the following ways:
(a) Domestic waste carries pathogens of diseases which cause diseases in aquatic animals.
(b) Fertilisers and pesticides cause eutrophication which reduces oxygen available to aquatic animals.
(c) Industrial wastes carry toxins that harm the aquatic organisms.

Q.4. During summer, if you go near the lake, you feel relief from the heat, why?
Ans: Air above the land gets heated up during day and starts rising and creates a region of low pressure. But the lake does not get heated so quickly and thus, air above the surface of lake moves to fill the area above the land. Therefore, a cold breeze flows from lake to land during summer days, gives relief to people standing near the lake.

Q.5. 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.
Ans: During day, the air above the land gets heated quickly and starts rising. This creates a region of low pressure, as a result air above the sea rushes into to fill this area of low pressure. This movement of air from one region to the other creates winds.
But at night, air over land cools down fast but air over sea cools slowly and hence remains hot. This creates low pressure over sea and air moves from land to sea, which cause wind.

Q.6. 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.
Ans
: (a) Lichens and (b) Mosses can grow on stones.
Lichens and mosses release substances which breakdown the stones resulting in the formation of soil. The mode of action here is chemical.

Q.7. Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?
Ans: Abiotic factors — Sun, water, wind.

Biotic factors — Lichens, mosses, trees, shrubs and herbs.

Q.8. All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.
Ans: The inorganic substances enter plants through the process of photosynthesis. The inorganic substances enter plants from air (C02) and water as ions by absorption of roots from soil. Herbivores eat these plants as food. Carnivores eat herbivores for survival. Thus, all organisms are basically made up of C, N, S, P, H and O which pass from plants to other organisms.

Q.9. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
Ans: Gases maintain consistency in the atmosphere through biogeochemical cycling where there is repeated circulation of biogenetic nutrients between biotic and abiotic components of the environment.

Q.10. Why does moon have very cold and very hot temperature variations, i.e. from - 190°C to 110°C even though it is at the same distance from the sun as the earth?
Ans: Due to absence of atmosphere on the moon, it gets heated up as soon as sun rays fall on its surface and cools down immediately when there is no sunlight.

Q.11. Why do people love to fly kites near the seashore?
Ans: Due to the regular unidirectional wind from sea to land, it helps the kite to fly high and the wind also provides comfort by making the seashore cool during daytime.

Q.12. Why does Mathura refinery pose problems to the Taj Mahal?
Ans: Mathura refinery releases toxic gas (like oxides of sulpliui) which causes acid rain and hence causes corrosion of the marbles of Taj Mahal. Thus, Mathura refinery poses problem to Taj Mahal.

Q.13. Why do lichens not occur in Delhi whereas the; commonly grow in Manali or Darjeeling?
Ans: Lichen is a bio-indicator and sensitive to S02 pollution from automobiles. Delhi has maximum number of automobiles, hence has highly polluted environment. But in Manal and Darjeeling, the atmosphere is humid anc sulphur dioxide pollution is low and so lichens grow there easily.

Q.14. Why does water need conservation even though large oceans surround the land masses?
Ans: Marine water is unfit for human and plant consumption. So, the terrestrial organisms have to depend on freshwater resources. Therefore, limited freshwater resources need conservation to cater to the demands.

Q.15. There is mass mortality of fishes in a pond. What may be the reasons?
Ans: There is mass mortality of fishes in a pond because of:
(a) throwing of industrial waste.
(b) flow of pesticide rich water from crop fields.
(c) thermal pollution
(d) addition of poisonous (mercury) compounds in water.
(e) blockage of fish gills with water pollutant.

Q.16. “Soil is formed by water,” If you agree to this statement then give reasons.
Ans: Yes, soil is formed by water in the following ways:
(a) Water causes 'wear off’ and ‘tear off ’ rocks over a long period of time.
(b) It also causes the rocks to rub against other rocks creating small particles which are tak en away downstream a n d deposited as soil.
(c) Water expands on freezing in crevices and crack of rocks that breaks the rocks into smaller pieces.

Q.17. Fertile soil contains of humus which is useful to soil and plants. Why?
Ans: 
Fertile soil has lots of humus Because:
(a) it is required for binding soil particles.
(b) it makes the soil porous for easy passage of roots.
(c) it is the source of minerals.
(d) it contains substances that promotes growth and development of plants.

Q.18. Why step farming is common in hills?
Ans: Step farming is common in hills to slow down the speed of rainwater currents and increasing the water absorption by soils. This is practicsed to check soil erosion through water currents on the slopes.

Q.19. Why are root nodules useful for the plants?
Ans: Root nodules occur in legume plants. In root nodules, nitrogen-fixing Rhizobium bacteria are present which increases the soil fertility. These bacteria picks up nitrogen from soil and converts it into organic compound. The roots absorb the organic compound and it is passed into plants and so legume plants become rich in proteins and other nitrogen compounds.

LONG ANSWER TYPE QUESTIONS

Q.20. How do fossil fuels cause air pollution?
Ans: (a) Burning of fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur. Inhalation of these gases is dangerous. These gases also dissolve in rain to give rise to acid rain.
(b) The combustion of fossil fuel also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons. The presence of high levels of all these pollutants, reduce visibility in cold weather where water also condenses out of air forming smog. Smog is an indication of air pollution.

Q.21. Discuss how you can contribute in reducing water pollution.
Ans: We can contribute in reducing water pollution as follows:
(a) The sewer lines should not be directly connected to the water body.
(b) We should not throw our garbages or domestic waste in the water body.
(c) We should prevent dumping of toxic compounds in the water bodies.
(d) Washing of clothes should be avoided near water bodies as it adds a lot of detergents to it.
(e) We should plant trees, shrubs and herbs near the banks of the river to check soil erosion.

Q.22. 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?
Ans: Glass being transparent allows sunlight to pass through it, hence heating the interior of the car. Since heat waves 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 coming from the sun that is having shorter wavelength than that emitted by the interior of the cars longer wavelength to which the glass is opaque. Therefore, heat from the can cannot move out.

Q.23. Justify “Dust is a pollutant”.
Ans: Dust is a pollutant because:
(a) it's present in air as suspended particles can cause allergy and other respiratory diseases.
(b) it also affects plant growth, by covering stomata on leaf surface.
(c) it acts as the carrier of toxic compounds like heavy metals.
(d) dust particles are eye irritants.
(e) it settles over plant foliage and reduces photosynthetic activity.

Q.24. Explain the role of the sun in the formation of soil.
Ans: The role of the sun in the the formation of soil is as follows: The rocks are heated by sun during daytime which makes them expand. At night after the sunset, the rocks cools down which makes them contract. This process of alternate expansion and contraction takes place everyday which result in cracks in the rocks and ultimately breaks it down to smaller particles which forms soil.

Q.25. Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Ans: CO2 is considered as a pollutant because the increasing concentration (more than normal) of CO2 is harmful. So, apart from CO2 being essential for photosynthesis, it is also a greenhouse gas. Higher concentrations of CO2 is one of the causes of greenhouse effect and global warming.

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