NCERT Solutions for Class 9th Science
Chapter 14 - NATURAL RESOURCES
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 How is our atmosphere different from the atmospheres on Venus and Mars?
Ans Earth is a habitable planet and no life is known to exist in Venus and Mars due to difference in their atmospheres. The difference essentially lies in the composition of air. Earth’s atmosphere is a mixture of many gases like nitrogen (78%), oxygen (21%), carbon dioxide (0.03%) and water vapour. On the other hand Venus and Mars have an atmosphere with major component as carbon dioxide (95-97%).
Q.2 How does the atmosphere act as a blanket?
Ans The atmosphere of the Earth keeps it warm enough to support life by acting as a blanket in the following ways:
1) The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year.
2) The atmosphere prevents the sudden increase in temperature during the daylight hours.
3) During the night, it slows down the escape of heat into outer space.
Q.3 What causes winds?
Q.4 How are clouds formed?
Ans A cloud is a large collection of very tiny droplets of water or ice crystals. The droplets are so small and light that they can float in the air. When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also get into the atmosphere because of various biological activities like transpiration etc. This air also gets heated rises up carrying the water vapour with it. As the warm air rises, it expands and cools. Cool air can't hold as much water vapour as warm air, so some of the vapour condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud.
Q.5 List any three human activities that you think would lead to air pollution.
Q.6 Why do organisms need water?
Q.7 What is the major source of fresh water in the city/town/village where you live?
Ans River is the major source of fresh water.
Q.8 Do you know of any activity which may be polluting this water source?
Q.9 How is soil formed?
Q.10 What is soil erosion?
Q.11 What are the methods of preventing or reducing soil erosion?
Q.12 What are the different states in which water is found during the water cycle?
Q.13 Name two biologically important compounds that contain both oxygen and nitrogen.
Q.14 List any three human activities which would lead to an increase in the carbon dioxide content of air.
Q.15 What is the greenhouse effect?
Ans Green House Effect: It may be defined as the natural process of trapping the reflected radiations by the earth’s atmosphere and keeping it warm enough to support life. Without this process, life would not have been possible on the earth. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The gases responsible for this like CO2, methane, nitrous oxide are called green house gases. Due to excessive level of these gases especially CO2, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.
Q.16 What are the two forms of oxygen found in the atmosphere?
EXERCISES
Q.1 Why is the atmosphere essential for life?
Q.2 Why is water essential for life?
Q.3 How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Q.4 You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Q.5 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 pollution?
Q.6 Write a note on how forests influence the quality of our air, soil and water resources.