NCERT Solutions Class 9th Science Chapter – 14 Natural Resources Notes

• Living resources → Biotic → E.g., Plants, Animals
• Non-living resources → Abiotic

• Air (Atmosphere)
• Water (Hydrosphere)
• Land (Lithospehre)

• Air pollution
• Water pollution
• Land pollution

• Insecticides
• Pesticides

Natural Resources
The resources available on the earth and the energy from the sun are necessary to meet the basic requirements of all life forms on the earth.
The stocks of nature which are useful to mankind are known as natural resources. E.g., air, water, soil, minerals etc.
What are these resources on the earth?

• The outermost crust of the earth is called the lithosphere.
• Water covers 75% of the earth’s surface. It is also found underground. These comprise the hydrosphere.
• The air that covers the whole of the earth like blanket is called the atmosphere.
• When these three sphere interact with each other it lead to the formation any biosphere.

Biosphere
All living things on earth together with atmosphere, the hydrosphere and the lithosphere interact and make life possible is known as biosphere.

Components of Biosphere can be grouped as:
Biotic components: Plants and animals.
Abiotic components: Air, water and soil.

AIR

• Air is a mixture of different gases. Nitrogen-78% oxygen-21% CO₂-0.04% water vapour & other insert gases.
• Air contains oxygen which is essential to living organisms for respiration (break down of glucose). So it is called breath of life.

Role of Atmosphere

• Air is a bad conductor of heat. It keeps the average temperature of the earth constant during the day and even during the course of the whole year due to green house effect.
• Prevents the sudden increase in temperature during day time and during the night, it slows down the escape of heat into outer space. If there is no atmosphere then the temperature may varies from 190°C to -110°C.

The Movement of Air: Winds

• During the day, the direction of wind is from sea to land. This is because the air above the land gets heated faster and starts rising. As this air rise a region law pressure is created and air over the sea move into this area of low pressure.
• During the night, the direction of wind is from land to sea. This is because at night, air above land get cool faster than on water.
• The movement of air from one region to the other creates winds. (moving air is called wind)
• All the movement of air resulting in diverse atmospheric phenomena.
• Other factor influence wind are: Rotation of earth, position of various mountain range.

• Rain is formed by evaporation condensation and precipitation of water through water cycle in which distribution of water takes place. Rain is very important for agriculture processes and recharge ground water.
• We should conserve rain water by constructing dams, pools, plantation etc.

• An increase in the content of harmful substance (pollutants) above the permissible limit in the air like carbon dioxide, carbon monoxide, oxides of sulphur, nitrogen, fluoride, lead, nickel, arsenic and dust particles etc. is called air pollution. It may cause:

In Humans: Respiratory and Allergic problems, high blood pressure, eye irritation, cancer etc.
In Plants: Reduced growth, degeneration of chlorophyll, mottling (patches/ spots of colour) of leaves. Presence of Lichen indicate air pollution level.

• When fossil fuels are burnt, gases like sulphur dioxide and nitrogen dioxide (NO₂) are released in the atmosphere.
• These gases dissolve in Rain water and form nitric acid and sulphuric acid. Which make Rain water acidic. this phenomenon is called Acid Rain.

• There keeps the earth warm by trapping the solar energy (heat) and keep the earth temperature normal even in the absence of sunlight.
• An Increase in carbon dioxide (CO₂):
  (i) intensifies green house effect.
  (ii) leads to global warming and increase in average temperature of earth.
  (iii) may lead to melting of polar caps and sub-merging number of coastal cities.

• Ozone layer is present in the stratosphere which is a part of our atmosphere from 16 km to 60 km above sea level.
• Ozone is an allotrope of oxygen. Its molecule is made up of three oxygen atoms. Molecular formula is O₃.
• Ozone layer absorbs the ultra-violet rays coming from the sun and protects living being from their harmful effects like skin cancer, cataract in eyes, weaken immune system. etc.
• The decline of ozone layer thickness in Antartica was first observed in 1985 and was termed as ozone hole.

• Excessive use of CFCs (Chloro Fluoro Carbon) in refrigerators, jet planes, spray cans, fire extinguishers. etc.
• Nuclear explosion
• CFC combine irreversibly with oxygen in stratosphere and thus causes O₃ depletion.

• About three-fourth of the earth surface is 75% are covered with water.
• It is present underground, (acquifer) a very large area on the surface (sea, ocean etc.) and also in the form of water vapour in the atmosphere.

• It maintains a normal temperature of the body.
• All cellular processes take place in a water medium.
• All the reactions that take place within our body and within our cells occur between substances that are dissolved in water.
• Water forms the habitat of many plants and animals.

• Dumping of wastes from the industries into water bodies. (industrial waste, i.e.) Heavy metal used in dye of textile and paper manufacturing etc.
• Warm water released form Thermal power plant.
• Washing of clothes near water bodies and emergence of idol.
• Spraying chemical in water field leads to cutrification.
• Dumping household wastes into the water bodies (domestic waste) sewage waste.

Causes

• Over grazing of land exussive deforestation.
• Removal of top soil by wind and water.
• Due to lack of trees the upper layer of soil is eroded by air and water.
• Leaving land uncultivated for long time.

• The flow of substances from non-living to living and back to non-living is called the cycling of substances.
• A constant interaction between the biotic and abiotic component of biosphere create a sustain, stable system known as biogeochemical cycle.

• The whole process in which water evaporates condensed and precipitate and falls on the land as rain and later flows back into the sea via rivers is known as water cycle.
• When sun shines, water evaporates continuously from the water bodies and forms water vapour. This water vapour rises up and goes into the atmosphere.
• The plants absorb water from the soil and use it during the process of photosynthesis. They also loose water by the process of transpiration.
• The process of respiration, Precipiration and Transpiration from the living organising. These water vapour produces water vapour which goes into the atmosphere..
• The rises up and condensed which precipitate in the form of rain. During winter, the water falls down in the form of dew or snow.
• All of the water that falls on the land does not immediately flow back into the sea. Some of it seeps into the soil and becomes part of the underground reservoir of fresh water.
• The underground water is again taken by plants and water cycle continues.

The percentage of oxygen in air is 21%.

• The cyclic process by which oxygen element is circulated continuously through the living and non-living components of the biosphere constitutes oxygen cycle. Two natural process help in oxygen cycle:

Respiration and Photosynthesis
Respiration decay of dead organisms release CO, and water Vapour.

• The carbon dioxide and water are used by the green plants during the process of photosynthesis. They give out oxygen during this process. which became part of atmosphere and again used by living beings.

Thus, the oxyen cycle keeps repeating in nature.

Carbon Cycle

about 0.03-0.04% carbon is present in the atmosphere in the form of CO2.

• Carbon cycle maintains the balance of the carbon element in the atmosphere. Carbon is found in various forms on the earth.
• Carbon occur as carbonates and bicarbonate salts in minerals.
• Carbon is the essential part of nutrients like carbohydrates, fats, proteins, nucleic acids and vitamins.
• Carbon cycle keeps the level of CO₂ constant in the atmosphere.

The sequence in which nitrogen passes from the atmosphere to the soil and available for organisms, and then is eventually released back into the atmosphere, is called nitrogen cycle.

• Nitrogen makes up 78% of the earth’s atmosphere.

Atmosphere

• Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins and chlorophyll.
• Plants and animals cannot utilize atmospheric nitrogen readily.
• It has to be fixed by some organisms called nitrogen fixers.
• Nitrogen-fixing bacteria like Rhizobium live in symbiotic association in the root nodules of certain leguminous plants.
• These bacteria convert atmospheric nitrogen into Nitrate and Nitrite ions which is utilized readily by plants.
• Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90% of nitrogen fixation.
• Lightning plays an important role in nitrogen fixation. When lightning occurs, the high temperature and pressure convert nitrogen and water into nitrates and nitrites and are readily used by aquatic plants and animals.
• Ammonification: It is the process by which soil bacteria decompose dead organic matter and release ammonia into soil.
• Nitrification: It is the process by which ammonia is converted into nitrites and nitrates.
• Denitrification: It is the process by which nitrates are converted into atmospheric nitrogen (N₁).