NCERT Solutions for Class 9 Science - Natural Resources

Q1. How is our atmosphere different form the atmospheres on Venus and Mars?
Ans. Our atmosphere contains gases like nitrogen, oxygen, carbon dioxide, water vapour and other gases in very small amount. Atmospheres of Venus and Mars have about 95% of carbon dioxide. So, life is not possible there.
 

Q2. How does the atmosphere act as a blanket?
Ans. The atmosphere acts as a blanket in the following ways: (1) It maintains the temperature on the surface of the earth during day and night time.
(2) It contains Ozone in the upper layer which protects life from harmful ultraviolet radiation.
 

Q3. What causes winds?
Ans. The uneven heating of the atmosphere in different regions of the earth causes wind. The rotation of earth and presence of mountain ranges also helps in the formation of wind, its blowing direction.
 

Q4. How are clouds formed?
Ans. During day time water from different sources like pond, lake, river, sea, well etc get evaporated and this water vapour rises up with the hot air. At a particular height the air cools and the water vapour condenses to form minute droplets and form clouds. When these water-drops become heavy, they precipitate and fall down as rain.
 

Q5. List any three human activities that you think would lead to air pollution.
Ans. Three human activities which leads to air pollution are (1) Burning of fuels like coal, petroleum, kerosene.
(2) Smoke released from industries
(3) Emissions from vehicles.
 

Q6. Why do organisms need water?
Ans. Organisms need water for the following activities:
(1) All cellular processes occur due to water.
(2) Transportation of substances in our body takes place by dissolving in water.
(3) Terrestrial animals require fresh water for transportation of minerals and for getting rid of waste from their body.
(4) Plants require water for photosynthesis.
 

Q7. What is the major source of fresh water in the city/town/village where you live?
Ans. The major sources of water are
(a) Water in the form of snow, ice-covered mountains.
(b) Underground water well.
(c) Surface water like in lakes, rivers, ponds.
(d) Rainfall.
(e) Stored rain water in tanks, dams.
 

Q8. Do you know of any activity which may be polluting this water source?
Ans. Yes, the water is polluted by (a) sewage
(b) dumping waste in river
(c) factory waste etc.
 

Q9. How is soil formed?
Ans. Factors that helps in the formation of soil and the process of formation are:

(1) Sun: The sun heats up rocks during the day so that they expand. At night these rocks cool down and contract, this causes cracks in the rocks.

(2) Water: Water during rainfall enter these cracks, if this water freezes, it exerts pressure on the cracks and the rocks break. When water flows, it wears the hard rock and carries small particles of rock down stream.

(3) Wind: Strong winds erode rocks down, which rub with each other and small particles are carried away by wind.

(4) Living Organisms: Like lichen grows on the surface of the rock, they release certain substances that causes the rock surface to powder down and form a thin layer of soil.
 

Q10. What is soil erosion?
Ans. The removal of top soil by air, wind, water is called soil erosion.
 

Q11. What are the methods of preventing or reducing soil erosion?
Ans. Methods to reduce soil erosion: (1) Soil should have some vegetations like grass growing on it, so that it does not get carried away by rain water or wind.

(2) Afforestation or planting of trees, so that roots hold the soil and prevent soil erosion.
 

Q12. What are the different states in which water is found during the water cycle?
Ans. Various states in which water is found during the water cycle are

(1) Water in liquid state present in various sources- lakes, rivers, underground water.

(2) Water vapour–gaseous state, water evaporates from water bodies and due to transpiration by plants.

(3) Clouds–condensed water vapour is present in clouds.

(4) Water as rain or snowfall.
 

Q13. Name two biologically important compounds that contain both oxygen and nitrogen?
Ans. Two biologically important compounds that contain both oxygen and nitrogen are DNA, protein, carbohydrates.
 

Q14. List any three human activities which would lead to an increase in the carbon-dioxide content for air?
Ans. (1) Burning of fuels like coal, petrol, diesel.

(2) Breathing releases CO2, exercises, which increases the breathing rate. (3) Using air conditioner, releases CO₂ in air.
 

Q15. What is the greenhouse effect?
Ans. Gases like CO₂ and methane trap sun’s radiation and don’t allow it to go back. This causes warming of atmosphere. This effect is called greenhouse effect.
 

Q16. What are the two forms of oxygen found in the atmosphere?
Ans. Oxygen is present in free form like O₂ (oxygen molecule), Ozone (O₃) and combined form like oxides of metals and non-metals e.g. CO₂, NO₂, SO₂, H₂O.

NCERT Textual Questions Solved

Q1. Why is the atmosphere essential for life?
Ans. Atmosphere is very important for sustaining life because

(1) It contains various gases like O₂, CO₂, N₂ which are required for various life processes by plants and animals.

(2) CO₂ gas is used by plants to prepare food by the process called photosynthesis.

(3) Oxygen is required for burning, combustion and respiration.

(4) Ozone layer is acting as a protective layer, which avoids/prevents harmful U.V rays to enter the earth’s atmosphere.

(5) CO₂ dissolved in water forms carbonates which is required by marine animals to form shells.
 

Q2. Why is water essential for life?
Ans. (1) About 70% weight of human being is due to water.

(2) All cellular processes takes place in water as medium.

(3) All reactions take place within our body and within the cells occur between substances that are dissolved in water.

(4) Transportation of substances from one form to another takes place due to water.

(5) Terrestrial life-forms require fresh water for the transportation of substances and also to get rid of high amounts of wastes.
 

Q3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Ans. All living organisms are directly or indirectly dependent on soil. Plants obtain water and minerals from the soil and prepare food for themselves and animals.
Other organisms that live in water are not totally independent of soil because the microbes growing on the soil in water are the primary producers in the soil which start the food chain and even other microbes that live in soil help in the decomposition of dead plants and animals in water to return the nutrients, elements back to the water.
 

Q4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Ans. Historical data on weather is stored in computers. These help in creating a model for weather pattern. Based on temperature humidity and wind speed of a given time frame, these data help meteorologists forecast the weather.
 

Q5. We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollutions?
Ans. If the human activities which leads to increasing level of air, water and soil pollution is spread in wider area then the pollutants will spread more, but yes, if it is limited and confined to a place then the soil and water pollution can be controlled to some extent and air pollution can also be minimised.
 

Q6. Write a note on how forests influence the quality of our air, soil and water resources.
Ans. Role of forest:

Air: (a) It helps in purifying the air by absorbing pollutants.

(b) It adds oxygen to the air and takes carbon-dioxide gas during photosynthesis. Therefore greenhouse effect is controlled.

(c) Transpiration helps in the formation of clouds, maintains the temperature of surrounding area and gives cooling effect.

Soil: (a) Plants in forest hold the soil thereby preventing soil erosion.

(b) It holds the soil which helps in increasing the underground water level.

(c) Adds nutrients to the soil as lot of vegetation present in forest gets decomposed.

Water: Forest helps in bringing rain and increasing the level of water in underground levels.