NCERT solutions for class 9 science
Chapter 14-Natural Resources-Exercise Solutions
NCERT TEXTBOOK EXERCISE Page Number-201-202
Q. 1. Why is the atmosphere essential for life?
Answer. Atmosphere is essential for life for the following reasons:
(i) Oxygen, which is required for the survival of every living organism is present in the atmosphere.
(ii) Atmosphere works as an insulator. It keeps the average temperature of the earth fairly constant during the day and night by preventing escape of heat into outer space.
(iii) Atmosphere also acts as protective blanket for the Earth. It absorbs most of the harmful radiations such as ultraviolet (UV) radiations coming from the sun. It results in the Earth receiving just the right amount of heat and sun’s rays, which helps in the climate control and allows the living organisms to exist.
Q. 2. Why is water essential for life?
Answer. Water is essential for life because:
(i) It is an important medium for all life processes.
(ii) Water acts as universal solvent and helps in providing many minerals required for proper functioning of the body.
(iii) We are dependent on water for many activities such as drinking, cooking, agriculture, transportation, production of hydel power, etc.
Q. 3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer. Man and animal obtain their food from the plants (cereals, vegetables, grass, etc.) grown on the soil. These plants obtain their food from the nutrients found in soil. In addition, soil also contains various micro-organisms which derive their food from the soil. Thus all living organisms depend on soil for their survival.
Soil is essential for all living organisms whether they are aquatic or terrestrial. Soil play important role in biogeochemical cycle which is a main source of recycling of nutrients from atmosphere to soil and then to water.
Aquatic plants obtain their nutrients from the bottom of that water body and these aquatic plants are source of food for the aquatic animals. In this way soil is essential for the aquatic organisms as well.
Q. 4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer. Weather observatories collect information regarding the pattern of temperature, speed of wind, air pressure, ocean features and all other features which can affect the weather. This information is collected by remote sensing and weather fore casting satellites. The information collected is then send to the meteorological departments which prepare a weather report which is further transmitted through radio and television.
Q. 5. We known 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?
Answer. Isolation of these activities which are causing pollution of air water and soil to a specific and limited area can reduce pollution to some extent but even this is not a permanent solution of the problem of pollution, because pollutants released after the decomposition of these wastes will recycle through soil, water and atmosphere. Thus, they will come back to the place from where they have been removed. Therefore, there should be a permanent procedure for the removal of pollutants.
Q. 6. Write a note on how forests influence the quality of our air, soil and water resources?
Answer. Forests influence the quality of our air, soil and water resources in the following ways:
(i) Carbon dioxide-oxygen balance in the atmosphere: Forests have large number of trees, shrubs and herbs. They take in CO2 and give out O2 during photosynthesis in day light. Thus, oxygen is consumed during combustion and respiration is replenished by forests.
(ii) Prevention of soil erosion : Forest trees and other plant roots bind the soil particles.
They form a vegetation cover over the fertile top soil. Thus, they prevent, removal of top soil and consequently soil erosion.
(iii) Replenishment of water resources : Forest trees are large in number and give out enormous amount of water during transpiration in the from of water vapour. The water vapour helps in the formation of clouds which on precipitation causes rain. If forests are cut and not replinshed there will be reduction in rain fall and change in climate.