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  • z

    Chapter 1: Natural Resources: Air, Water

    and Land

    1

    Lets Revise

    1. Natural Resources: i. The elements available in the nature that fulfill the basic needs of living things on

    earth, thereby allowing life to sustain on earth are known as Natural Resources.

    ii. Air, water and land are called the earths atmosphere, hydrosphere and lithosphere respectively.

    iii. Living things and the parts of the lithosphere, hydrosphere and atmosphere which they occupy are together called as biosphere (In Greek, bios = life,

    sphaira = sphere).

    2. Air:

    i. Air in the atmosphere around the earth comprises of various gases such as nitrogen,

    oxygen, carbon dioxide, six inert gases, nitrogen dioxide, sulphur dioxide, water

    vapour and dust particles.

    ii. Proportion of gases in air is as follows:

    Spheres of Earth Proportion of gases

    Troposphere 80% of the total mass of gases in the air

    Stratosphere 19% of the total mass of gases in the air

    Mesophere and Ionosphere Proportion of gas goes on decreasing

    Exosphere Lacks gases completely

    iii. Uses of the different gases in air are as follows:

    Gas Uses

    Nitrogen

    Helps living things to build necessary proteins.

    Useful in production of ammonia also, in food industry for air

    tight packaging of food items.

    Oxygen Essential for respiration (breathing in living things) and for

    burning (combustion).

    Carbon dioxide For photosynthesis (in plant) and is a major constituent of fire

    extinguishers.

    Argon Used in electric bulbs.

    Helium Used for obtaining low temperature and for generating lift in

    airships.

    Neon Used in street lights and decorative lights.

    Krypton Component of fluorescent tubes.

    Xenon Used in flash photography.

    iv. Atmosphere acts as an important filter, because:

    a. It allows light and heat to reach earths surface in quantities required for life to

    sustain on earth.

    b. Also, it prevents harmful elements from reaching the earth.

    v. Fog, clouds, snow and rain are produced in atmosphere.

    vi. Air pollution: Any undesirable change in the normal composition of the air by

    addition of harmful gases is known as air pollution.

    1. Natural Resources : Air, Water and Land

  • Std. VI: General Science Workbook

    2

    vii. Air pollution is caused by harmful gases given out through combustion of fuels in

    vehicles and in big industries. It is also caused due to incomplete combustion of fuels

    like coal and wood.

    viii. Nitrogen dioxide, carbon dioxide, carbon monoxide, sulphur dioxide and soot are

    some harmful air pollutants.

    3. Ozone layer:

    i. Ozone layer is present in the lower part of the stratosphere.

    ii. It functions as a shell to protect the earth from harmful ultra violet rays coming from

    the sun.

    iii. Chemical gases like Carbon tetrachloride, Chlorofluorocarbons used in air

    conditioners and refrigerators mix with air and destroy ozone layer.

    4. Water:

    i. It is said that Water is life, because it is absolutely essential for survival of living

    things.

    ii. Water is colourless, tasteless and odourless. It is universal solvent (many substances

    readily dissolves). It occurs in three states such as solid (ice), liquid (water) and

    gaseous (water vapour).

    iii. The blood of animals and sap in plants contain a very high proportion of water.

    iv. Water available on earth:

    a. Water in seas and oceans: 97%

    b. Ground water, frozen state (ice): 2.7%

    c. Fresh, drinking water: 0.3%

    Thus, only 0.3% of total water covering the earths surface can be utilized for the purpose

    of drinking.

    5. Water cycle:

    i. Water cycle that leads to rainfall is the major source of water on earth.

    ii. Water evaporates from the oceans, gets stored in the clouds and condenses as rain.

    Thus, fresh water enters the ocean, thereby completing the cycle.

    iii. Rain water also seeps into the ground, thereby increasing the ground water level.

    This gives rise to other sources of water like rivers, ponds, springs, lakes, streams.

    iv. Uncontrolled use of water for the ever increasing population, industry and farming

    has resulted in shortage of water.

    v. Thus, it is necessary to use water sparingly. Water can be percolated in the ground by

    blocking it. Stored water does not become stale at once, thus it can be reused

    wherever possible.

    6. Land:

    i. Land is seen in the form of stones, soil, big rocks.

    Both plants and animals need land. Humans live on

    land as well as utilize it for other purposes like

    shelter, farming etc. Land is an important source of

    minerals, crude oil and natural gas, which are useful

    for humans in many ways.

    ii. Layers of land:

    a. Humus: Topmost mature layer. It is most

    fertile layer formed by decomposition of

    animals and plants.

    Humus

    Immature soil

    Bedrock

    Top soil

    Layers of land

    Layer of soil and

    small rocks

  • z

    Chapter 1: Natural Resources: Air, Water

    and Land

    3

    Fill in the blanks

    *1. The layer of ozone gas absorbs --------------------------------

    rays that come from the sun to the

    earth.

    *2. Of the total water available on the earth, fresh water forms --------------------------------

    percent.

    *3. Both --------------------------------

    and --------------------------------

    constituents are present in the

    soil.

    Summative Assessment

    Q

    b. Top soil: Full of sand, soil, small stones, worms and insects.

    c. Immature soil: Comprises of soil and pieces of bedrock.

    d. Bed rock: A layer with less soil and more rocks. Minerals are obtained from this

    layer. Responsible for colour and texture of the soil.

    iii. Soil formation is slow, continuous and

    natural process. It takes about a

    thousand years for a 2.5 cm thick layer

    of mature soil to form.

    iv. Heat, cold and water breakdown the

    bedrocks into pieces. From these

    pieces stones, sand and soil particles

    are formed.

    v. Microbes, worms and insects as well as

    rodents like mice and rats are found

    here. Roots of trees also contribute in

    weathering of rocks.

    vi. Soil erosion occurs due to natural

    calamities like earthquakes, fluids, storms and human activities such as mining,

    farming and deforestation etc. It makes land barren.

    vii. Thus, to prevent soil erosion, it is necessary to plant more trees, as the roots of

    trees/plants/ grasses and bushes hold the soil particles tightly.

    viii. Formation of fossil fuels: Geographical upheavals led to burial of the trees and

    animals deep inside the land. Burial of the remains of plants and animals for many

    ages led to formation of fossil fuels.

    ix. Fossil fuel gives us many useful substances such as petrol, diesel, kerosene, paraffin,

    tar and wax.

    x. All living things utilize the natural resources for their survival but the availability of

    natural resources in the environment is limited.

    For example Oxygen 21%

    Fresh water 0.3%

    Land 29%

    Thus, one need to use these resources judiciously.

    xi. India Meteorological Department (IMD) was established in 1875 for studying the

    weather in Indian subcontinent.

    Stones, Sand,

    Soil

    Breaks down into

    Rock

    Wind Cold

    Formation of

    layer of soil

    Microbes

    Rodents

    Roots of

    plants

    Heat Water

  • Std. VI: General Science Workbook

    4

    4. Atmosphere, hydrosphere and lithosphere constitute the --------------------------------

    .

    5. Gases are absent in --------------------------------

    layer of atmosphere.

    6. Fog, snow and rain are formed in --------------------------------

    .

    Right or Wrong ? If Wrong, write the correct sentence

    *1. Land and soil are the same thing.

    Ans: ---------------------------------------------------------------------------------------------------------------

    ---------------------------------------------------------------------------------------------------------------------

    *2. The water in a lake is called ground water.

    Ans: ---------------------------------------------------------------------------------------------------------------

    ---------------------------------------------------------------------------------------------------------------------

    *3. It takes about 1000 years to form a 25 cm thick layer of soil.

    Ans: ---------------------------------------------------------------------------------------------------------------

    *4. Radon is used in decorative lights.

    Ans: ---------------------------------------------------------------------------------------------------------------

    5. Weathering of rock is the initial process of soil formation.

    Ans: ---------------------------------------------------------------------------------------------------------------

    6. Hydrosphere occupies 71% of the earths surface.

    Ans: ---------------------------------------------------------------------------------------------------

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