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Natural Resources - Class 9 Science Notes

Introduction

  • Life on the earth depends on the resources like air, water, soil, etc.

  • The resources available on the earth and the energy from the sun are necessary to meet the basic requirement all life forms on the earth.

  • The stock of nature which are useful to mankind are known as natural resources. Example: air, water, soil, minerals, etc.


Natural Resources


The outer crust of the Earth.

Lithosphere

Water covers 75% surface of the earth and also found underground.

Hydrosphere

The air that covers the whole of the earth like a blanket

Atmosphere

Biosphere

All living things (life supporting zone) on the earth together with the atmosphere, the hydrosphere and the lithosphere interact and makes life possible is known as Biosphere


It consists of:

i. Biotic component: Animals and Plants

ii. Abiotic component: Air, Soil, Water, etc




Atmosphere (Air)

  • Air is mixture of different gases like nitrogen, oxygen, carbon dioxide, etc.

  • Air contains oxygen which is essential to living organisms for respiration. So, it is called ‘the breath of life’.

Role of atmosphere

  • Air is a bad conductor of heat. It keeps the average temperature of the Earth fairly steady during the day and even during the whole year.

  • It prevents the sudden increase in temperature during day and night, it slows down the escape of heat into outer space.

Example: the moon, with no atmosphere, the temperature ranges from -1900C to 1100C.


Movement of Air: Winds

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

  • During the day, the direction of the wind is from sea to land: This is because the air above the land gets heated faster and starts rising.

  • During the night, the direction of the wind is from land to sea: This is because at night both land and sea starts to cool.

Air pollution and its causes

An increase in the harmful substances (or pollutants) in the air like carbon-dioxide, carbon-monoxide, oxides of sulphur, oxides of nitrogen, fluoride, lead, nickel, arsenic, suspended particulate matter, etc. causes air pollution.


Air pollution can cause

In Humans

In Plants

Respiratory and renal problems, high blood pressure, eye irritation, cancer.

Reduced growth, degeneration of chlorophyll, mottling (patches / spots of colour) of leaves.

Rain

- Rain is formed by evaporation and condensation of water through the water cycle in which distribution of water takes place.

- Rain is very important because it carries out all agriculture processes in the plants.


  • Acid Rain:

- When sulphur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere on burning the fossil fuel and gets dissolved into water, it forms sulphuric acid (H2SO4) and nitric acid (HNO3).

- The condensed water along with these acids result into acid rain.






Water

  • Water is the most unusual natural compound found on the earth and which fulfils almost various demands of different living things – so called a Wonder Liquid.

  • Around three fourth (i.e., 75%) of the earth surface is covered with water.


Necessity of Water

  • It maintains a uniform temperature of body.

  • All cellular process takes place in a water medium.

  • All reactions that take place within our body and within our cells occur between substances that are dissolved in the water.

  • Water forms the habitat of many plants and animals.


Water pollution and its causes

When water becomes unfit for drinking and other uses, then water is said to be polluted.

  • Dumping of waste from houses or industries into water bodies.

  • Washing of clothes in or near the water bodies.

  • Spraying chemicals in water field.

  • Deforestation

  • Acid rains

  • Fuel spillages into large water bodies.


Soil

Soil is the portion of earth surface consisting of disintegrated rock and decaying organic material. It provides the support for many plants and animals.


The factors or processes that makeup the Soil:


  • The Sun: The Sun heats up rocks during the day so that they expand. At night, these rocks cool down and contract.


Since all the parts of rock do not expand and contract at the same rate, this result in the formation of cracks and ultimately huge rocks break up into smaller pieces.


  • Water: It helps in two ways; one, water gets into the cracks formed in the rocks due to heating by the Sun and on freezing it widens the cracks.


Two, flowing water wears away even hard rocks over a long period of time. This carries big and small particle of rocks that gets rubbed against other rocks and the resultant abrasion causes rocks to wear down into smaller and smaller particles.


  • Wind: Wind carries sand from one place to other. The strong winds also erode down the rocks.


  • Living organism: Organisms like Lichen, Moss grows on the surface of rocks and they release certain substance that causes the rock surface to powder down and form a thin layer of soil.

The roots of big trees sometimes get into the cracks and forces it to expand while growing.


Soil Profile:

  • Soil Profile has different horizons as follows:

  • O horizon (Surface layer)

  • A horizon (Topsoil): The topmost layer that contains humus and living organism in addition to soil particles is called the Topsoil.

The dark organic matter obtained from decayed living organism is called humus.

  • B horizon (Subsoil)

  • C horizon (Parent material)

  • R horizon (Bedrock)


Causes of Soil Erosion:


Carrying away of upper fertile layer of soil by wind, water, human activities and wrong agricultural practices is called Soil Erosion.


i. Overgrazing of land.

ii. Removal of topsoil by wind and water.

iii. Due to lack of trees upper layer of soil is eroded by air and water.

iv. Leaving land uncultivated for long time.



Biogeochemical cycles


Biogeochemical cycles mainly refer to the movement of nutrients and other elements between biotic and abiotic factors.


Biogeochemical cycles are basically divided into two types:

  • Gaseous cycles – where the reservoir is atmosphere or hydrosphere.

Includes Carbon, Oxygen, Nitrogen, and the Water cycle.

  • Sedimentary cycles – where the reservoir is the earth.

Includes Sulphur, Phosphorus, Rock cycle, etc.



The Water-Cycle (Hydrologic cycle)

  • Hydrological cycle is continuous cycle of water in the earth-atmosphere system which is driven by solar energy.

Water released into atmosphere

Water consumed from atmosphere

Evaporation

Photosynthesis

Transpiration from plants

Agriculture (utilize ground water)

Perspiration from animal body

Irrigation (from rivers, canals)

Precipitation (rainfall)

Household purposes


The Nitrogen Cycle

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

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

  • Nitrogen is essential constituents of proteins, nucleic acids like DNA and RNA, vitamins and chlorophylls.

  • Plants and animals cannot utilize the atmospheric nitrogen directly. Firstly, this nitrogen is converted into ammonia which readily utilized by plants as it is soluble into water.

This process is carried out by certain organism (mainly bacteria) known as Nitrogen Fixing Bacteria. These bacteria may be free-living or associated (generally symbiotic association with leguminous plants).

Example: Rhizobium, Azotobacter, Clostridium, Cyanobacteria.

  • From the nitrogen fixation 90% of nitrogen gets fixed into the soil.

  • Lighting plays an important role in nitrogen fixation, when lighting occurs, the high temperature and pressure converts nitrogen and water into nitrates and nitrites. These are water-soluble and readily available to aquatic plants and animals.

  • Ammonification: The process in which soil bacteria decomposes dead organic matter and releases ammonia into soil.

  • Nitrification: the process by which ammonia is converted into nitrite and nitrates.

  • Denitrification: the process by which nitrates are converted into atmospheric nitrogen.



The Carbon Cycle

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

o It occurs in the elemental form as Diamond and Graphite.

o Carbon can also occur as carbonates and bicarbonates in the minerals.


Utilize carbon from atmosphere

Releases carbon to atmosphere

Photosynthesis: Land – Plants

Sea – Phytoplankton

Respiration

Organic storage in plants, fossil formation - coal, mineral oil and gas.

Decomposition

Combustion

Weathering

Volcanic eruption



Greenhouse Gas Effect

- The greenhouse effect is the way in which heat is trapped close to Earth's surface by “greenhouse gases.”

- The main greenhouse gases whose concentrations are rising are carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and ozone in the lower atmosphere.



Effect of greenhouse gases:

i. Leads to global warning.

ii. Increase average temperature of the earth.

iii. Sub-merging of the coastal lines.

iv. May lead to melting of polar ice-caps.


Green house Green Effect. Explained!



The Oxygen Cycle

- The cyclic process by which oxygen element is circulated continuously through living and non-living component of biosphere constitutes oxygen cycle.

- The percent of the oxygen present in air is 21%.

- It is in the elemental form O2 (diatomic molecule).

Release of oxygen in atmosphere

Consumption of oxygen fromatmosphere

Photosynthesis

Carbon dioxide and water is used by green plants to produce oxygen.

Respiration:

All living organisms use oxygen to respire.

Volcano

Combustion:

This process takes place in presence of oxygen.

Formation of oxides of Nitrogen

Decomposition



Ozone Layer

  • Ozone (O3) – an allotrope of Oxygen – three atoms of oxygen bound in non-linear fashion.

  • Ozone in troposphere = degrade air and helps to form smog

  • Ozone in stratosphere = protects life on earth by absorbing UV radiations.

  • The decline of the ozone layer thickness in Antarctica was first observed in 1985 and was term as Ozone Hole.

  • Equilibrium between formation and destruction of ozone, has been upset by influx of certain substances into atmosphere. It is known as Ozone Depletion.

What is Ozone Layer Depletion and its Effects?


Reason for Ozone Depletion:

i. Excessive use of CFCs (Chloro Fluoro Carbon) in refrigrators, jet planes, spray canes, fire extinguishers, etc.

ii. Nuclear explosion.

iii. Naturally occurring Ozone Depleting Substances (ODS):

a. Hydrogen oxide

b. Methane

c. Hydrogen

d. Nitrogen oxide

e. Chlorine monoxide.


Measures to mitigate Ozone Depletion:

i. Montreal Protocol, 1987

The Montreal protocol on substances that deplete Ozone layer was designed to reduce production and consumption of Ozone depleting substances such as CFCs in order to reduce their abundance in atmosphere, there by protect earth’s fragile ozone layer.


ii. Kigali Amendment 2016

Amendment to the Montreal Protocol to eliminate planet – warming HFC gases.