In the following section, you will get NCERT Class 9 Science Natural Resources Notes pdf. These notes have been prepared by the subject experts who have been teaching science at various levels for the last 10 years. We are sure that you will find these notes helpful
NCERT Class 9 Science Natural Resources Questions and Answers
The following section contains NCERT Class 9 Science Natural Resources Questions and answers. These notes of Natural Resources Class 9 are all about the natural resources of the environment. You will learn topics like Global warming, Pollution, Ozone depletion, atmosphere and its constituents from the following section.
Also Check: Structure of the atom class 9 science notes pdf
How is our atmosphere different from the atmospheres on Venus and Mars?
In our atmosphere, gases like Nitrogen, Oxygen, Carbon dioxide and water vapour are present. These all help in existence of life on it.
However, atmospheres of Venus and Mars have 95 to 97% carbon dioxide. Other life supporting gases does not exist there. As compared to this on earth, air forms the blanket of Nitrogen (78-80%), Oxygen (20.92%), Carbon dioxide (0.03%), Argon (0.93%) and other trace components.
How does the atmosphere act as blanket?
Our atmosphere acts as a blanket as it keeps the average temperature of the earth fairly constant during the day. The atmosphere prevents the sudden increase in temperature during daylight and slows down the escape of heat into outer space during night.
What causes winds?
Winds are caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from higher to the lower pressure area, resulting in winds of various speeds.
How are clouds formed?
When warm air rises it expands and cools. Cool air can’t hold as much water vapours as warm air, so some of the vapours condense into tiny pieces of dust floating in the air and form tiny droplet around each particle. Billions of droplets combine to form clouds.
List any three activities that you think would lead to air pollution?
The three activities are: (i) Burning of fuels (ii) Urbanisation (iii) Deforestation.
Why do organisms need water?
Water is the basic necessity for all living organisms, because:
- It helps in digestion and absorption of food.
- All cellular processes need water as a medium.
- Plants need water to carry photosynthesis and animals need it so they will live.
- Water is also used for replenishing and transportation of nutrients.
What is the major source of fresh water in the city/town/village where you live
Underground water and water in rivers, lakes and ponds.
Do you know any activity which may be polluting water source?
1, Use of fertilizers and pesticides.
2, Sewage and waste of factories are dumped into rivers which cause water.
How is soil formed?
Soil formation involves two processes namely weathering and pedogenesis.
(1) Weathering:- It is the process of weakening and breaking rocks into smaller fragments.
Weathering is of three types namely physical weathering, chemical weathering and biological weathering.
Physical weathering involves the agents such as sun, water, wind etc.
(a) Sun: Under the influence of solar radiations the rocks heat up and expand. At night these cool down and contract since all parts of the rocks do not expand and contract at the some rate cracks appear in the rocks and ultimately rocks break up into smaller fragments.
(b)Water: In the fast flowing water, rocks get rubbed against each other thus breaking into smaller fragments.
(c) Wind: Strong winds cause weathering of rocks by eroding them.
The chemical weathering involves the chemical processes such as hydrolysis, hydration, carbonation, oxidation, reduction, chelation etc.
Chemical processes involved in soil formation
Hydration:- As a result of taking water the rock swells this swelling causes disruption of rocks.
Fe2O3 → Fe2O3. 3H2O
Oxidation reduction:- Some oxidation reduction reactions such as reversible change of Fet to Fez+ cause disruption of rocks because Fe?+ is more soluble than Fe+
Carbonation:- Some chemicals bring about carbonation for example the reversible change of CaCO3 > Ca(HCO3)2 leads to solution loss of limestone as the hydrogen carbonate is more soluble than carbonate.
Chelation:- Some chemical exudates produced through biochemical activities of microorganisms such as bacteria, lichens etc. extract the metals in their elemental form and this process is called chelation.
Biological Weathering involves biological agents like lichens, bryophytes and other plants.
Lichens growing on rocks secrete acids which cause weathering of rocks. Plant roots when penetrate in the cervices of rocks increase in growth this causes pressure on the sides of rocks thus breaking them into smaller fragments.
(2)Pedogenesis:- Pedogenesis is largely a biological phenomenon. During this phenomenon living organisms such as lichens, bacteria, fungi, algae, micro-arthropods, molluscs etc, as a result of secretion of organic acids, enzymes, CO2, production addition of organic matter after their death, bring about geochemical, biochemical and biophysical processes.
Due to all this the crusts of weathered rock debris are converted to true soil consisting of a complex mineral matrix in association with a number of organic compounds and a rich microorganism population.
What is soil erosion?
The removal of top fertile layer of soil from its original position to another with the help of certain agents such as strong winds and fast running rain water is called soil erosion. Soil erosion normally occurs in bare areas i.e, areas without plant cover it is because the bare top soil is loose and thus can be carried away by strong winds or fast moving water of heavy rains.
Agents of Soil Erosion?
The various agents involved in soil erosion are
- Strong Winds:- Uncovered loose soil get eroded when it is exposed to strong winds, the winds carry away the soil particles to other places.
- Heavy rains:- When heavy rains fall on the uncovered top soil it washes down the soil into streams and rivers etc.
- Suspended cultivation:- Some times due to certain reasons the farmers are not able to cultivate
another crop after the first one is harvested. The agricultural fields remain barren and become susceptible to soil erosion.
- Human actions:- Certain human actions such as deforestation, overgrazing etc. expose the soil for external agencies (wind and rain) for erosion.
- Frequent Floods:- Frequent floods in rivers erode the top soil in the fields near the river banks and carry it away.
Effects of soil erosion
- Landslides in hilly areas
- Decrease in fertility of soil
- Decrease in yield of crops.
- Silting of water reservoirs.
What are the methods of preventing or reducing Soil erosion?
1, Strip Cropping:- It involves the planting of crop in rows or strips to check flow of water.
2, Mulching:- It is a process in which grass or stalks of plants are put over the barren soil so that it may not be eroded. Mulching also helps in retaining moisture in the soil.
3, Afforestation:- The plants on the land slow down the speed of rain water and in this way check the soil erosion. The roots of plants hold the soil firmly which is not prone to erosion.
4, Contour Farming:- In hilly areas the cultivation is done on the slopes of hills. To reduce the soil erosion while ploughing contours in the form of circles are made this process is called contour farming.
5, Crop rotation:- Growing one crop after another leaving no land fallow susceptible to soil erosion is called crop rotation.
6, Embankment along the river banks.
7, Proper drainage canals around the fields.
What are the different states in which water is found during the water cycle?
Different states are solid, liquid and gas.
Name two biologically important compounds that contain both oxygen and nitrogen?
Amino Acids, Ribonucleic Acid and Deoxyribonucleic Acid.
List any three human activities that would lead to an increase in the CO2 content of air?
Deforestation, Urbanisation, Burning of fuels.
What is Green House Effect?
The greenhouse effect is a natural phenomenon which occurs when the greenhouse gases present in the Earth’s atmosphere trap solar radiation.
It is caused by gases in the air that trap energy from the sun. These heat trapping gases are called green house gases. The most common green house gases are water vapour, carbon dioxide and methane.
What are the two forms of oxygen found in the atmosphere?
Two forms of oxygen found in the atmosphere are Oxygen (O2) and Ozone (O3).
Define Atmosphere? Why is the atmosphere essential for life?
The envelop of air that surrounds our earth is called atmosphere. The atmosphere serves as:
- Protective blanket filtering harmful U.V radiations from the sunlight that fall on the earth.
- Place for many climatic events like convection currents, cloud formation, thundering, precipitation etc.
- Reservoir of important elements which are essential for the life such as N2, O2, C, H2 etc.
Importance of Air
- The atmospheric blanket around the earth acts like a window glass pan. It allows most of the radiations to enter right up to the earth’s surface. But does not allow long wave radiations emitted by the earth to escape into the space. These outgoing fractions are trapped by green house gases present in atmosphere. This down word flux of the radiations called green house flux keeps the earth warm.
- Air is a mixture of gases. Oxygen gas present in air is the essential component of living creatures to sustain.
- CO2 is an essential requirement for the process of photosynthesis in plants.
- The blanket of air absorbs the U.V. radiations, thus protects the living things from diseases caused by the U.V radiations coming from the sun.
Why is water essential for life?
Water is one of the basic necessities of life. Without water we can not think of life. Water exists on the earth as ground water and as surface water, we get underground water through springs and tube wells.
Surface water is present in lakes, ponds, streams, on the peaks of mountains in the form of snow and ice water is present in air in the form of vapours in the oceans, seas and rivers.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as resource?
Plants depend upon soil from where they get minerals, water and air. They are required for growth of plants. Animals (herbivores) depend on the plants. Other animals (carnivores) depend on the herbivores. Organisms which live in water are not totally dependent upon soil as resource.
However decomposers like bacteria etc. which show their presence at the sediments of water bodies decompose complex dead decaying organic matter into simpler inorganic substances. They get dissolved in water and are made available to aquatic plants as nutrients.
You have seen weather reports on television and in newspapers. How do you think, we are able to predict the weather?
Information is gathered by meteorological laboratories in various parts of country for factors like:
- Direction and speed of wind.
- Relative humidity.
- Patterns of cloud formation.
- Daily minimum and maximum temperature.
- Depression zone in a particular area.
This all data helps in prediction of rain and other weather related proccsses. It also helps in finding the low or high pressure areas.
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?
By isolating human activities to specific and limited areas for reducing pollution of air, water bodies and soil should not be seen as complete success.
It may help in reduction of only soil pollution. Air and water pollution cannot be checked by doing so. It is due the reason that air and water pollution are not affected by the local factors, but are influenced by the global factors.
Write a note how forests influence the quality of our air, soil and water resources.
Forests maintain the CO2, and O2 balance of atmosphere. They need CO2 for the process of photosynthesis and release O2 into the atmosphere by photolysis of water during this process.
Plants check soil erosion as roots of such plants bind the soil.
They maintain the fertility of soil and help in recharging of water resources. They maintain the water cycle in nature.
By preventing soil erosion, forests maintain the quality of water resources. There is less silting due to this.
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