Chapter 14, NATURAL RESOURCES
CBSE (NCERT) Textbook Exercise Solution
Q.1: Why is the atmosphere essential for life?
Ans: The multilayer gaseous envelope (or blanket) surrounding the planet earth is called atmosphere. Atmosphere filters sunlight, reaching the earth affect climate and is a reservoir of several elements which are essential for life. Oxygen, nitrogen, water vapour etc. present in the atmosphere are required by most living beings for their survival. The atmosphere prevents sudden increase in temperature during daylight. It also slows down the escape of heat thus, keeps the average temperature of the earth fairly steady. The ozone layer of the atmosphere saves the living forms from the harmful effects of ultra-violet rays.
Q.2: Why is water essential for life?
Ans: Organisms need water because it plays a vital role in the reaction taking place within organism’s cells and body. Water acts as a universal solvent, providing a medium for the chemical reactions to occur. Substances are also transported from one part of body to the other in the dissolved state. Therefore, it is necessary for the organisms to maintain a distinct level of water within their bodies to stay alive.
Q.3: How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Ans: The top surface layer of earth capable of supporting plant life is called soil. Soil is a complex mixture, comprising of minerals (45%), organic matter (5%), water (25%), air (25%) and living organisms. It is an important resource that determines the diversity of life in an area. Plants are dependent on the soil from where they obtain various types of minerals, water and air. All these three components are essential for the growth of plants. Animals (herbivores) depend on plants for food. Other animals (carnivores) depend on these herbivores. Hence, all living organisms directly or indirectly depend on the soil.
Aquatic organisms are not entirely independent of soil as a resource. Microscopic decomposers (e.g. fungi, archaebacteria and bacteria) present in the bottom sediments of water bodies decompose dead, decaying organic matter into simple, inorganic substances (minerals). The latter get dissolved in water and are available as nutrients for aquatic plants and they indirectly through plants to animals. Also, water bodies get supply of minerals from soil through rivers, spring etc. without which minerals present in the water bodies will exhaust. Aquatic green plants and animals get these minerals from water.
Q.4: You have seen weather reports on television and in news paper. How do you think we are able to predict the weather?
Ans: We daily see weather reports on television and news papers. This information about the weather is recorded by meteorological laboratories present in different parts of the country. Information such as direction and speed of wind, average daily minimum and maximum temperature, relative humidity, patterns of cloud formation, depression zones over an area, etc. are recorded with the help of instruments and are then displayed on televisions, published in news papers or broadcasted on the radio. This meteorological information helps us to predict the weather and to act accordingly. For example a farmer can decide his next step for agriculture according to latest weather report and may be benefitted.
Q.5: We know that many human activities lead to increasing levels of pollution of air, water bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Ans: We have studied that many human activities lead to increase in the levels of pollution of the air, water bodies and soil. Isolating such activities to specific and limited areas may help in reducing only soil pollution. However, air and water pollution can not be checked. Moreover, air, water and soil are naturally inter-related resources. They do not remain confined to specific areas after pollution. For instance, air pollution brings about global environmental changes such as,
(1) Acid rainfalls;
(2) Global warming due to increase in the concentration of green house gases (CO2, CH4 and Chlorofluorocarbons i.e. CFCs) in the atmosphere;
(3) Depletion of ozone layer.
In the same way, water keeps moving in streams, rivers and oceans. It distributes wastes to far-off places from the point of their discharge. Similarly, underground-water pollution due to sewage, industrial wastes and agricultural percolation will affect large areas.
Q.6: Write a note on how forests influence the air, soil and water resources.
Ans: Forest is a large area covered thickly with trees and other plants such as, shrubs and grasses. Forest is a renewable natural resource. Forests influence the air, water and soil resources in following ways:
(1) Forests shape natural environment by influencing factors like temperature, humidity and precipitation.
(2) Forests shape the soil environment by affecting its composition, structure, the chemical properties, water contents, etc.
(3) Forests play important role in running the biogeochemical cycles of water, carbon, nitrogen, oxygen, and other elements.
(4) Forest plants maintain the carbon dioxide and oxygen balance in the atmosphere.
(5) Roots of forest plants bind the soil and prevent soil erosion. In this way they help in maintaining the fertility of soil. Many bacteria present in root nodules (e.g. Rhizobium bacteria in root nodules of leguminous plants) replenish to the soil.
(6) Forests check floods, land-slides and shifting of sand and silting of rivers.