CBSE CLASS 9 CHAPTER 14 NOTES
CHAPTER
14
CBSE SCIENCE
CLASS 9
NATURAL RESOURCES
INTRODUCTION
·
Earth – only planet – life exists
·
Life on earth – dependent on many factors –
temperature, water, food, etc.,
·
Resources on earth & energy – from sun – necessary
to meet the basic requirements – all life forms on earth
RESOURCES ON THE EARTH
·
Land, water & air
·
Lithosphere – outer crust of the earth
·
Hydrosphere – 75% of earth covered by water + under
ground water
·
Atmosphere – with that covers the earth like a blanket
·
Living things found – where the 3 exists
BIOSPHERE
·
Life supporting zone on earth – atmosphere,
hydrosphere & lithosphere interact – makes life possible – Biosphere
·
Biosphere – biotic & abiotic components
·
Biotic – living things
·
Abiotic – non-living – air, water, soil, etc.,
AIR – THE BREATH OF LIFE
·
Air – mixture of gases – nitrogen, oxygen, carbon di
oxide & water vapour
·
Composition of air on Earth – one of the important
reason – for life on earth
·
Venus & Mars – no life – major component of
atmosphere – CO2 – 95 to 97% of the atmosphere
·
Eukaryotic cells & many prokaryotic cells – use
oxygen for break down of glucose & get energy – release CO2 (by product)
·
Combustion – O2 is used up – produce CO2 (burning
fuels, forest fires)
·
Despite this - % of CO2 in the atmosphere – is a mere
fraction of a percent
·
CO2 is fixed in 2 ways
·
Green plants – convert CO2 into glucose – presence of
sunlight
·
Marine animals – use carbonates dissolved in sea water
– to make shells
ROLE OF THE ATMOSPHERE IN CLIMATE CONTROL
·
Atmosphere – protective layer – safe guards the earth
·
Air – poor conductor of heat
·
During day – it prevents – sudden increase in
temperature of the earth
·
During night – prevents the heat from escaping to the
outer space – thereby preventing sudden cooling
·
It keeps the average temperature of the earth – steady
·
Moon – same distance from the sun like earth – but has
no atmosphere – their temperature ranges from 12℃ (day) to
-157℃ (night)
MOVEMENT OF AIR – WINDS
·
Moving air – called wind
·
Winds – caused – due to even heating of atmosphere
·
Air moves from – high pressure area – to low pressure
area
·
During day – air above the land – gets heated faster –
starts rising – creates low pressure near land – so, air from the sea comes to
low pressure area – over land
·
So, wind blows from sea to land – Sea breeze
·
During night – earth cools faster – sea remains warm –
air above the sea – still hot – starts rising – creates low pressure – over the
sea – so, air from the land comes to the low pressure area – over sea
·
So, wind blows from land to sea – Land breeze
·
Therefore – movement of air – caused by – uneven
heating of the atmosphere – in different regions of the earth
·
Other factors
that influence winds
·
Rotation of the earth
·
Presence of mountain ranges – in the path of winds
RAIN
·
During day – when water bodies are heated – water
evaporates – goes into the air
·
Air gets heated – hot air rises up – carries water
vapour with it
·
As air rises – expands & cools – water vapour
condenses – form tiny droplets
·
Condensation of water – occurs around some small
particles – called ‘nucleus’ – usually dust & other suspended particle
·
Once water droplets are formed – grow bigger – when
they become heavy – they fall down as rain
·
When temperature of air – too low – precipitation
takes place – forms snow, sleet or hail
·
Rainfall patterns – decided by the wind patterns
·
In India – rains are mostly brought by – south west or
north east monsoon
AIR POLLUTION
·
Fossil fuels – like coal & petroleum – contain
small amounts of Nitrogen & sulphur
·
When fuels are burnt – produces oxides of nitrogen
& sulphur
·
Inhalation of these gases are dangerous – also these
gases dissolve in rain – gives acid rain
·
Burning fossil fuels – increases the suspended
particles in air
·
Suspended particles – unburnt carbon particles or
substances called hydrocarbons
·
Presence of these high level pollutants – lowers
visibility – in cold weather – called smog (smoke + fog) – indicates air
pollution
·
Regular inhalation of pollutants – increases
allergies, cancer & heart diseases
·
Increased harmful substances in air – air pollution
·
Lichen (fungi + blue green algae) – presence of this
organism in barks of trees – indicates absence of air pollution
WATER – A WONDER LIQUID
·
75% of Earth – occupied by water
·
Water found – earth’s surface, underground, atmosphere
(as water vapour)
·
Most water – seas & oceans – saline
·
Most fresh water – frozen in ice-caps – at poles &
in snow covered mountains
·
Underground water, water in rivers, lakes & ponds
– fresh water
·
Availability of fresh water – varies from place to
place
NECESSITY OF WATER
·
All cellular processes – takes place in a water medium
·
Water – maintains uniform temperature of the body
·
All the reactions – takes place in our body &
within our cells – occur between substances that are dissolved in water
·
Substances – travel from one part of the body to other
– in dissolved form
·
Organisms – need to maintain level of water in the
body – to stay alive
·
Water – very essential for animals & plants to
survive on land
·
Water – forms habitat – many plants & animals
·
Availability of water – decides the number of specie
that lives in a particular area – also decides diversity of life
·
Other factors – temperature, nature of soil – also
decides sustainability of life in a region
WATER POLLUTION
·
An undesirable change – in physical, biological or
chemical properties of water – due to addition of foreign organic or inorganic
substances – that adversely affects the aquatic life – makes water less fit /
unfit for use – water pollution
MAIN CAUSES FOR WATER POLLUTION
·
Addition of harmful substances – like fertilizers
& pesticides (agriculture) – or mercury salts (paper industries)
·
Removal of desirable substances – like oxygen from
water – dissolved oxygen – used by aquatic plants & animals – removal of O2
– adversely affects aquatic life
·
Change in water temperature – aquatic organisms – used
to live in a certain range of temperature – sudden change in temperature –
affects aquatic life forms & their breeding
SOIL
·
Uppermost layer of earth’s crust –supports terrestrial
plants, animals & microorganisms – soil
FORMATION OF SOIL
·
Minerals are found in huge rocks
·
Over thousands & millions of years – rocks are
broken down – by physical, chemical & some biological processes – fine
particles of soil are formed
PROCESSES THAT MAKES THE SOIL
SUN
·
Sun heats up rocks – during day – expands
·
Night – cools rocks - contracts
·
All the parts of the rocks – donot expand &
contract – at the same rate
·
Results in – formation of cracks – rocks breaks into
smaller pieces
WATER
·
Helps to form soil – in 2 ways
·
(i)Water – gets in the cracks of rocks – formed due to
uneven heating by sun
·
Water freezes – cracks widen
·
when water flows over hard rocks – over long period –
wears away the rocks – carries small & big particles of rocks downstream
·
The rocks – rub against other rocks – breaks into
smaller & smaller particles – deposits further down its path
·
Soil – found in places – far away from parent rocks
WIND
·
Like water – winds – also erode rocks – wear them down
·
Wind – carries sand from one place to another – like
water
LIVING ORGANISMS
·
Living organisms – influence the formation of soil
·
Lichen – grows on surface of rocks
·
While growing – release some substances – powders the
rock surface – forming soil
·
Moss (small plant) – grows on this surface – cause
rocks to break further
·
Roots of big Trees – grow under the cracks of rocks –
as roots grow bigger – cracks become bigger
COMPOSITION OF SOIL
·
Soil – mixture of small particles of rocks, decayed
living organisms (humus) & various forms of microscopic life
·
Type of soil – decided by – average size of the
particles in it
·
Quality of soil – decided by – amount of humus &
microscopic organisms in it
·
Humus – helps the soil to become porous – allow water
& air to penetrate deep inside
COMPOSITION OF SOIL
·
Minerals – present in the soil – depends on the rocks
– from which the soil is formed
·
Nutrient, humus, depth of soil – decides which plants
– will thrive
·
Top most layer of soil – contains soil particles,
humus & living organisms – called Topsoil
·
Quality of topsoil – decides biodiversity in that area
SOIL POLLUTION
·
Use of fertilizers & pesticides – over a long
period – destroy soil structure – by killing soil microorganisms – that recycle
soil nutrient
·
Also kills earthworms – makes rich humus
·
Fertile soil – turns barren – if sustainable practices
– not followed
·
Removal of useful components – addition to other
substances – which adversely affects – fertility of soil – & kill
microorganisms in it – soil pollution
SOIL EROSION
·
Removal of the topmost layer of soil by wind, water or
other activities – Soil erosion
CAUSES OF SOIL EROSION
·
Factors responsible for soil erosion
·
Over grazing of land
·
Removal of topsoil by wind (storms) & water
(flood)
·
Deforestation
·
Leaving land uncultivated – for long time
EFFECTS OF SOIL EROSION
·
Lose of fertility – due to loss of topmost fertile
soil – results in Desertification
·
Landslides – in hilly areas
·
Clogging of water drains & water reservoirs – by
washed off soil
PREVENTION OF SOIL EROSION
·
Soil can be prevented from soil erosion – by following
these methods
·
Intense cropping
·
Terrace farming
·
Afforestation
·
Making strong embankments – along river banks
BIOGEOCHEMICAL CYCLES
·
Constant interaction between biotic & abiotic
components – in a biosphere – makes it dynamic but stable system
·
Interactions – transfer of matter & energy –
between different components of biosphere
THE WATER CYCLE
·
The whole process – in which – water evaporates &
fall on the land as rain - & water flows back into the sea – via rivers –
known as ‘Water Cycle’
MAIN STEPS IN WATER CYCLE
(a)
EVAPORATION
·
Water on earth – changes to vapour – due to sun’s heat
– rises above
(b) TRANSPIRATION
·
Plants – absorb water – through roots – gives off
excess water – in the form of vapour – through stomata in leaves
(c)
PRECIPITATION
·
Process of condensation of water vapour in atmosphere
– into liquid – which fall down – as rain, snow, sleet or hail
(d) PERCOLATION & ABSORPTION
·
Some of the rain water – soaks into ground – reach
underground water – some gets absorbed by plants, crops & trees – rest
flows downhill – runoff to reach seas – to complete the water cycle
NITROGEN CYCLE
·
The sequence in which – nitrogen passes from
atmosphere – to soil & organisms – then back again released back into the
atmosphere – Nitrogen cycle
·
Nitrogen gas – 78% of our atmosphere
·
Nitrogen – a part of many molecules essential for life
– like proteins, nucleic acids (DNA & RNA) & vitamins
·
Nitrogen – also found in – biologically important
compounds – alkaloids & Urea too
·
But atmospheric nitrogen – cannot be directly taken up
by the life forms – they have to be converted to nitrates & nitrites
STEPS INVOLVED IN NITROGEN CYCLE
NITROGEN FIXATION
·
Process – by which – atmospheric nitrogen – converted
into forms – that can be easily absorbed by organisms (nitrates & nitrites)
·
Nitrogen fixation – carried out in following ways
·
by Lightning
·
When lightning occurs – high temperature &
pressure – convert nitrogen – into oxides of nitrogen – gets dissolved in water
– gives nitric & nitrous acids – fall along with rain – used by various
life forms
·
by Bacteria
·
Molecular nitrogen – converted into nitrates &
nitrites – by free living bacteria or bacteria like Rhizobium – present in root
nodules of legumes
·
Some bacteria – converts nitrogen gas to ammonia (NH3)
– plants can use
NITRIFICATION
·
Process – by which – ammonia – converted into nitrites
& nitrates
ASSIMILATION
·
Nitrogen compounds – used by plants & animals
·
Plants – form amino acids – with nitrates &
nitrites
·
Amino acids – used to make proteins – in plants
·
This process – called assimilation
AMMONIFICATION
·
Process – by which – soil bacteria decompose dead
organic matter – release ammonia – into soil
DENITRIFICATION
·
Process – by which – nitrates converted into
atmospheric nitrogen – completes the cycle
CARBON CYCLE
·
Process in which –carbon is moved from atmosphere into
the earth & its organisms – and then back again – Carbon cycle
IMPORTANCE OF CARBON
·
Carbon can be found on earth – as Carbondioxide
·
Carbonates & hydrocarbons - present in minerals
·
Present in all life forms – proteins, fats, vitamins
& carbohydrates
·
Internal skeleton (Endoskeleton) & External
skeleton (Exoskeleton) – in animals – made up of carbon salts
·
Plants – converts carbon into glucose – during
photosynthesis
·
Carbon cycle involves the following processes
(a) PHOTOSYNTHESIS
·
Plants – form their food – absorbing atmospheric
carbon – as CO2 gas – release O2 gas
(b) RESPIRATION
·
Plants & animals – respire – resulting in
breakdown of glucose – to release CO2, water & energy
(c) DECOMPOSITION
· Dead plants & animals – decompose – release carbon into environment
(d) COMBUSTION
·
Burning fossil fuels – release CO2 gas – as by product
(e) MOVEMENT OF CARBON FROM
ATMOSPHERE TO OCEANS
·
Oceans & other water bodies – soak about 1/4th
of CO2 – form carbonates
·
Thus, amount of CO2 formed – almost equal to amount of
CO2 consumed – hence % of it in air – remains same
GREEN HOUSE EFFECT
·
GREEN HOUSE House like structure – made of
transparent material (glass)
·
Provides plants – appropriate environment for growth –
in cold regions
·
Green house – traps heat inside – prevents from going
out
·
GREEN HOUSE EFFECT Several gases – present in
earth’s atmosphere – prevents the heat that enters the atmosphere from moving
out of it
·
Amount of these gases increases – atmospheric
temperature of the earth – rises
·
Leads to several problems – increase in sea levels –
due to melting of glaciers
·
This phenomenon – Green House Effect
·
GREEN HOUSE GASES
·
Gases that cause green house effect
·
Example: CO2, methane & ozone
GLOBAL WARMING
·
Phenomenon – in which – average temperature of the
earth increases – due to the presence of green house gases – Global Warming
EFFECTS OF GLOBAL WARMING & GREEN HOUSE EFFECT
·
Increase in average temperature of the earth
·
There is severe change in climate – affects
biodiversity
·
Melting of ice caps – major consequence
·
Increase in temperature of the oceans
·
Affects aquatic life
·
Many aquatic animals – cannot survive in hot water
·
Severe weather conditions
·
Many parts of the world – extreme hot/ extreme cold
climate – due to increase in earth’s temperature
·
Result – some places – receives heavy rainfall –
others face droughts
·
Warmer winters
·
Winter season – many places – decreased – due to
global warming
·
Infertile Lands
·
Irrigational areas – may become infertile – due to
change in weather
·
Affects – agricultural pattern & availability of
food – all over the world
EFFECTS OF GLOBAL WARMING & GREEN HOUSE EFFECT
·
Effect on animals
·
Migration & hibernation – affected due to climate
change
·
Global warming – can lead to – extinction of animals –
due to their inability to adapt to the changing environment
·
Flooding of islands & coastal areas
·
Melting of ice caps – increases sea level – all over
the world
OXYGEN CYCLE
·
Cyclic process – by which – oxygen element –
circulated continuously – through living & non-living components of the
biosphere – thereby maintains – amount of oxygen in the atmosphere
IMPORTANCE OF OXYGEN
·
Second most Abundant gas – in the atmosphere (21%)
·
Found in earth’s crust – as oxides in metals &
minerals
·
Found in combined form – in CO2
·
Found in biological compounds – proteins, nucleic
acids, carbohydrates & fats
·
Oxygen cycle involves the following steps
o RESPIRATION
·
All living organisms – take in simple sugars (glucose)
& oxygen – release CO2, water, energy
o COMBUSTION
·
During combustion (burning) – O2reacts with carbon –
form CO2 gas
o PHOTOSYNTHESIS
·
CO2 gas – absorbed by green plants in the presence of
sunlight – form carbohydrates & O2 – O2 liberated into atmosphere
OZONE LAYER
·
Elemental oxygen is diatomic – O2
·
Upper layer of the atmosphere – earth is covered by a
gas – called ozone (OR) – triatomic
·
Ozone is a poisonous gas – but it doesn’t affect life
– found far away from biosphere
·
Ozone layer – shield – prevents harmful UV rays of sun
– from reaching earth’s surface
OZONE LAYER DEPLETION
·
Discovered – ozone layer – getting thinner – depletion
·
A hole in ozone layer – found over Antarctica
CAUSES OF OZONE DEPLETION
·
CFCs – released due to industrial processes,
refrigeration, etc
·
Chlorine & Fluorine – not degraded by biological
process – on reaching ozone layer – reacts with it – form complex compounds –
depletes ozone
·
Ozone layer depletion – allows UV rays from sun – to
reach earth’s atmosphere
EFFECTS OF UV RAYS
·
Increase in risk of having skin cancer
·
Damaging the eyes
·
Weakens immune system
·
Skin allergies
·
Decay – growth of plants & animals
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