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 1/4^th 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