NCERT solutions for class 9 science : Intext Solutions

Chapter 14-Natural Resources-Intext Solutions

Q.1. How is our atmosphere different from the atmosphere on Venus and Mars?
Answer. On Venus and Mars the major component of atmosphere is carbon dioxide which constitute upto 95–97% of the atmosphere. While on earth carbon dioxide constitutes only a small fraction of the atmospheric gases, i.e., it constitutes only 0.03% of atmosphere gases. The main gases on earth are nitrogen (78.08%) and oxygen (20.95%). Presence of oxygen in high concentration makes it easy to breathe for living organisms. This difference in the concentration of oxygen and carbon dioxide differentiates atmosphere on earth from that
on Venus and Mars.
Q.2. How does the atmosphere act as a blanket?
Answer. The atmosphere acts as a blanket because:
(i) It keeps the average temperature of the earth constant during the day.
(ii) It prevents the sudden increase in temperature during the daylight hours.
(iii) During night, it shows down the escape of heat into outer space.
Q. 3. What causes winds?
Answer. Wind is caused by the movement of air from one region to another region. During the day the air above the land gets heated faster and starts rising, therefore, a region of low pressure is created below and air above the sea moves into this area of low pressure. Thus movement of air from land to upper region of atmosphere and from sea to the land causes wind.
Q.4. How are clouds formed?
Answer. When water bodies are heated during the day then a large amount of water evaporates and goes into the air. Some amount of water vapour also gets into the atmosphere because of various biological activities. The air gets heated and rises up carrying the water vapour with it. The air expands on rising and cools which causes the water vapour in the air to condense in the form of tiny droplets. These water droplets get bigger and from clouds.
Q.5. List any three human activities that you think would lead to air pollution.
Answer. (i) Deforestation i.e., cutting of forests leads to air pollution.
(ii) Burning of fuels like coal, petroleum, etc., leads to air pollution.
(iii) Smoke from industries leads to air pollution.
Q.1. Why do organisms need water?
Answer. Organisms need water to carry out the following activities:
(i) All cellular processes in an organism take place in a water medium.
(ii) Water acts as universal solvent and helps in transporting substances from one part of the body to another in a dissolved form.
(iii) Water is also required by organisms for many of their activities such as drinking, cooking, agriculture, transportation, production of hydel power etc.
Q. 2. What is the major source of fresh water in the city / town / village where you live?
Answer. Fresh water is present as ground water and surface water. In our city, we get fresh water
from rivers, lakes as well as underground reservoirs made by the engineers.
Q.3. Do you know of any activity which may be polluting this water source?
Answer. Water used for industrial purposes is discharged into the rivers, lakes, etc., after being used in production processes. The water may contain acid, alkalis, toxic substances, etc. Fresh water bodies are also the sites for the disposal of sewage and other domestic wastes. All these activities pollute the water sources.
Q. 1. How is soil formed?
Answer. Soil is formed from parent rock material over millions of years by a process called weathering.
In this process, rocks at or near the surface of the earth are broken down into small particles due to physical factors such as sun, wind, rain etc. and it is called physical weathering.
The small particles of rocks are then converted into fine particles of soil by the help of plants, animals and micro-organisms, this is called biological weathering.
Q.2. What is soil erosion?
Answer. Soil erosion is washing away of the top soil with flowing water or wind. If all the soil gets washed away, the rocks underneath are exposed. This results in the loss of a valuable resource, the top soil which contains humus and living organisms and it is the most fertile soil.
Q. 3. What are the methods of preventing or reducing soil erosion ? [H H H H H ]
Ans. Methods of preventing or reducing soil erosion ?
(i) It can be prevented by intensive cropping.
(ii) It can be prevented by providing proper, drainage canals around the fields.
(iii) Soil erosion in hilly areas can be prevented by practising terrace farming.
(iv) It can be prevented by planting trees and sowing grasses.
(v) It can be prevented by constructing strong embarkments along the river banks.
Q. 1. What are the different states in which water is found during the water cycle ?
Ans. States are :
(i) Gaseous state : In the form of water vapour which evaporates from the surface water.
(ii) Liquid state : It is formed by the condensation of water vapour and can be seen in the form of rain.
(iii) Solid state : It is formed by the freezing of liquid droplets in the upper layer of
atmosphere which can be seen in the form of snow, hail or sleet.
Q. 2. Name two biologically important compounds that contain both oxygen and nitrogen.
Answer. Proteins and nucleic acids (DNA and RNA).
Q.3. List any three human activities which would lead to an increases in the carbon dioxide content of air.
Answer. The three human activities leading to an increase in the carbon dioxide content of air are:
(i) Burning of fossil fuel, such as petrol, diesel and coal in various activities like
transportation and industrial processes.
(ii) Burning of wood and charcoal for heating, cooking etc.
(iii) Deforestation reduces the green plant and tree population and utilisation of
atmospheric $CO_{2}$ during photosynthesis.
Q.4. What is the greenhouse effect?
Ans. Greenhouse effect is an atmospheric phenomenon, in which an increases in the percentage of some gases such as carbon dioxide in the atmosphere causes the average temperatures to increases worldwide.
Q.5. What are the two forms of oxygen found in the atmosphere?
Answer. Elemental oxygen is normally found in the form of a diatomic molecule, i.e.,$ (O_{2}$) : But at the upper layers of atmosphere, there is another form of oxygen which is a triatomic molecules of oxygen and it is called ozone $ (O_{3}$). Thus, the two forms of oxygen found in the atmosphere
are $ (O_{2}$) and $ (O_{3}$) (ozone).