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CBSE NOTES CLASS 9 SCIENCE CHAPTER 14

NATURAL RESOURCES

Natural Resources

Earth

Biosphere

Air - the breath of life

Effects of air pollution

Importance of water

Formation of soil

Biogeochemical cycles

CBSE NOTES CLASS 9 SCIENCE CHAPTER 14

NATURAL RESOURCES

Natural Resources

The different resources available on the earth are land, water and air.

All of these three things are required for the existence of life.

Earth

Lithosphere: The outer crust of the Earth.

Hydrosphere: 75% of the earth’s surface is covered with water. This water along with underground water comprises the hydrosphere.

Atmosphere: The air covering of earth is called atmosphere.

Biosphere: The life-supporting zone of the earth where the atmosphere, hydrosphere and the lithosphere interact and make life possible is known as the biosphere.

Biotic components: The living things constitute the biotic components of the biosphere.

Abiotic components: The non-living things air, water and soil, rain etc. form the abiotic components of the biosphere.

Air - The Breath of Life

Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapours. On Venus and Mars carbon dioxide constitutes 95-97% of the atmosphere and there is no life.

Oxygen is consumed and carbon dioxide is produced in the atmosphere by following activities:

(i) Breakdown of glucose in presence of oxygen by organisms during respiration.

(ii) Combustion of fuels, including household activities, forest fires, industrial activities etc.

Carbon dioxide is fixed in two ways

Despite large production, the percentage of carbon dioxide in our atmosphere is a mere fraction of a percent because carbon dioxide is ‘fixed’ in two ways:

(i) Green plants convert carbon dioxide into glucose in the presence of Sunlight and

(ii) Many marine animals use carbonates dissolved in sea-water to make their shells.

The Role of Atmosphere in Climate Control

(i) Atmosphere keeps the average temperature of the earth steady during the day and whole year.

(ii) Atmosphere prevents sudden increase in temperature during daytime and sudden fall of temperature during night.

Moon has no atmosphere, its temperature ranges from -190°C to 110°C.

Movement of Air – Winds

The movement of air from one region to the other creates winds.

Reason: Sand and water do not heat up evenly. Also different parts of the earth do not receive sunlight equally. Because of this uneven heating there is movement of air and water which cause various climatic conditions like rain, winds, thunder etc.

When air is heated by radiation from the heated land or water, it rises. But since land gets heated faster than water, the air over land is also heated faster than the air over water bodies.

Sea Breeze

In coastal regions during the day, the air above the land gets heated faster and starts rising. A region of low pressure is created and air over the sea moves into this area of low pressure.

During the day, the direction of the wind would be from the sea to the land. This wind from sea to land is called sea breeze.

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Land Breeze

At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land. This results in wind from land to sea, which is called land breeze.

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Trade winds

Uneven heating – region near equator receives more heat than poles. As a result the air in equatorial regions rises and creates a low pressure. The cold air from polar regions rushes to take its place creating a wind. These winds are called trade winds.

But various other factors also influence these winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind.

Cloud Formation and Rains

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 gets into the atmosphere because of various biological activities like respiration, transpiration etc.

The hot air rises up carrying the water vapour with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets around dust and other suspended particles in the air, which act as nucleuses. This is cloud.

When the drops have grown big and heavy, they fall down in the form of rain.

When the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.

Rainfall Distribution in India

Rainfall patterns are decided by the prevailing wind patterns.

In large parts of India, rains are mostly brought by the southwest or northeast monsoons or sometimes due depressions in pressure.

All parts of India do not receive the same amount of rainfall. This affects the lives of people and animals as well as plants and crops.

Pollution

The addition of substances which have harmful or poisonous effects or removal of desirable substances from the environment is called pollution.

Causes of Air Pollution

Effects of Air pollution

Importance of water

Distribution of water is not uniform throughout the world, due to uneven rains and climatic conditions.

Other factors like the temperature and nature of soil also matter in deciding the sustainability of life in a particular region.

Water pollution

The main causes of water pollution are:

(i) The addition of undesirable substances to water-bodies. These substances could be

(a) The fertilisers and pesticides used in farming or

(b) They could be poisonous substances, like mercury salts which are used by paper-industries.

(c) These could also be disease-causing organisms, like the bacteria which cause cholera.

(ii) The removal of desirable substances from water-bodies. For example

(a) Dissolved oxygen is used by the animals and plants that live in water. Any change that reduces the amount of this dissolved oxygen would adversely affect these aquatic organisms.

(b) Other nutrients could also be depleted from the water bodies.

(iii) A change in temperature. Aquatic organisms are used to a certain range of temperature in the water-body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding. The eggs and larvae of various animals are particularly susceptible to temperature changes.

Eutrophication: Eutrophication is a condition in which high amount of fertilizers and chemicals in the water bodies leads to plants and algae on the surface of water bodies. It reduces the dissolved oxygen and nutrients from the water and adversely affects fish, plants and animal species.

Formation of soil

Soil is the most important natural resource which supplies nutrients to the life forms. Soil is formed by weathering of rocks in thousands of years, due to,

Humus: A dark-brown or black organic substance made up of decayed plant or animal matter is called humus Humus provides nutrients for plants and increases the ability of soil to retain water. Humus makes the soil porous and allows water and air to penetrate deep underground.

Topsoil: The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil. The quality of the topsoil is an important factor that decides biodiversity in that area.

Soil pollution

Removal of useful components from the soil and addition of other substances, which adversely affect the fertility of the soil and kill micro-organisms living in it, is called soil pollution.

Use of large amounts of fertilizers and pesticides over long periods of time can destroy the soil structure by killing the soil micro-organisms that recycle nutrients in the soil. It also kills the earthworms which are instrumental in making the rich humus.

Soil erosion

Removal of topsoil by wind, water or other activities is called soil erosion.

Roots of plants prevent soil erosion by firmly holding the soil particles. The large-scale deforestation destroys biodiversity and also leads to soil erosion.

Topsoil that is bare of vegetation, is likely to be removed very quickly by wind and water.

Soil erosion is accelerated in hilly or mountainous regions.

Harmful Effects of Soil Erosion

(i) The implications of soil erosion leads to removal of valuable topsoil. Crop emergence, growth and yield are directly affected by the loss of natural nutrients and applied fertilizers.

(ii) Seeds and plants can be disturbed or completely removed by the erosion.

(iii) Soil quality, structure, stability and texture can be affected by the loss of soil.

(iv) It affects the water-holding capacity of the soil, making it more susceptible to extreme conditions such as drought.

Methods of preventing soil erosion

(i) Forestation: Growing plant grass and shrubs

(ii) Build retaining walls or terraces for steep slopes

Biogeochemical cycles

Various biogeochemical cycles exist in the nature due to interaction between biotic and abiotic components of the biosphere to make a stable system.

(A) Water cycle

The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again.

The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.).

Plants also lose water to the air through transpiration.

Animals lose water due to respiration and perspiration.

The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea).

Some of the precipitation soaks into the ground. Some of the underground water is trapped between rocks or layers of clay which is called groundwater.

But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.

The water running off to sea dissolves lots of sand and chemicals, thereby making the sea water salty.

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(B) Nitrogen cycle

The series of processes by which nitrogen and its compounds are inter-converted in the environment and in living organisms, including nitrogen fixation and decomposition, is called nitrogen cycle.

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Nitrogen is found in biologically important compounds such as proteins, alkaloids and urea. Nitrogen is thus an essential nutrient for all life-forms and life.

However, other than a few forms of bacteria, life-forms are not able to convert the comparatively inert nitrogen molecule into forms like nitrates and nitrites which can be taken up and used to make the required molecules.

Nitrogen is used by life forms to carry out many of the functions of life.

It is converted or ‘fixed’ into compounds usable by living organism.

The process of converting nitrogen into its compounds is called nitrogen fixation.

Specialized bacteria fix the nitrogen, converting it to compounds, so that it can be used by plants.

It can also be done during lightning. The high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain.

After nitrogen is fixed, it can be absorbed and used by plants, and subsequently by animals.

Animal and plant waste and dead bodies are decomposed and the nitrogen is returned to atmosphere in its gaseous form.

The process of nitrogen being fixed, used by plants and animals, and later returned to the atmosphere is referred to as the nitrogen cycle.

(C) Carbon cycle

The series of processes by which carbon compounds are interconverted in the environment, involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.

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Carbon is incorporated into life-forms through the basic process of photosynthesis which is performed in the presence of Sunlight by all life-forms that contain chlorophyll. This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.

These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other molecules.

The carbon dioxide is produced during the process of respiration and goes into the atmosphere.

Carbon dioxide is also produced during burning of fuels.

Carbon dioxide is also found as carbonate and hydrogencarbonate salts in various minerals.

Carbon containing molecules like proteins, carbohydrates, fats, nucleic acids and vitamins are the basis of life.

The endoskeletons and exoskeletons of various animals are also formed from carbonate salts.

(D) Oxygen cycle

Oxygen cycle is a biogeochemical cycle that describes the movement of oxygen within the earth’s three main reservoirs – the lithosphere (land), the hydrosphere (water), and the atmosphere (air), which make up the earth’s biosphere.

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Plants produce oxygen during photosynthesis.

All organisms use oxygen for respiration.

When plants and animals die, they decompose. This process uses up oxygen and releases carbon dioxide into the air.

Combustion also uses up oxygen and releases carbon dioxide into the atmosphere.