Class 6 Science Chapter 11: Nature's Treasures
- 5 topics
- 100 MCQs
- 30 short answers
- 15 long answers
- 75 flashcards
- 25 games
- ~160 min read
- English
Air, and the Firki That Turns
Hold your breath and you find out how little time the body will wait. Air is a mixture, mostly nitrogen, and the part that keeps you going is only a fifth of it.
What you will be able to do
- I can explain why a person cannot go without air for more than a few minutes.
- I can give the composition of air and say which gas takes up most of it.
- I can describe how air makes itself noticed without ever being seen.
- I can explain how a firki and a windmill both work, and what a wind farm is for.
Key points
Air is not one gas but a mixture of several, and it surrounds the whole Earth.
Of every hundred parts of air, 78 are nitrogen, 21 are oxygen and 1 is everything else.
The last part is shared between argon, carbon dioxide and a few other gases.
Oxygen is what the body draws on to carry out its work, and most living beings need it.
A few days may pass without food or water, but only minutes without oxygen.
Air is never seen, only inferred, from rustling leaves and swaying clothes.
Moving air is called wind, gentle enough to be a breeze or fierce enough for a storm.
A wind farm is a stretch of land carrying many windmills, put there to make electricity.
Full explanation
A Village Where the Forest Begins
Bhoomi and Surya spend a vacation with their Ajji, whose village stands where the Western Ghats forest begins. The first thing they notice is the air. It is cooler than the air of the city, and it smells clean. Ajji tells them the place is full of treasures, and the air is one of them.
An Exercise to Start With
One morning Ajji is doing breathing exercises, and the children join her. Deep breath in, slow breath out, then a deeper one. Ajji says it fills the lungs with fresh air and keeps a person healthy. Then comes the part worth trying yourself: hold the breath as long as you comfortably can, and count.
What Holding It Tells You
Nobody manages it for long. Discomfort arrives quickly, and there is a reason. The air drawn in carries oxygen, and the body needs oxygen to carry out its work. Hold the breath and that supply is cut off, so the body is left short. Most other living beings are in the same position.
A Comparison Worth Remembering
Think about how long a person could manage without food. A few days, uncomfortable but survivable. Without water, fewer days than that. Without oxygen, a few minutes is all. The three needs are not equally urgent, and air is the one that cannot wait.
Something You Never See
Air is invisible, so it is noticed only through what it does. Leaves rustle on a tree. Clothes on a line sway. Switch on a fan and the pages of an open book start to flutter. Every one of those is air announcing itself without being seen at all.
Air on the Move Has a Name
Moving air is called wind. Sometimes it comes gently, and that is a breeze. Sometimes it comes hard, as in a storm. Same air, different speed, and the difference is easy to feel even though there is nothing to look at.
Not One Gas But Several
The air wrapped around the Earth is a mixture. Nitrogen is in it, and oxygen, and argon, and carbon dioxide, with a few more present only as traces. The name air covers them all together, which is why no single gas can be pointed to and called air.
Counting It in Hundreds
The proportions are set out on a grid of a hundred squares. Nitrogen takes 78 of them. Oxygen takes 21. That leaves exactly one square for argon, carbon dioxide and everything else put together. Seeing it drawn makes the balance obvious in a way a list of figures does not.
What Percentage Means
Percentage is the number of parts in every hundred, and the sign for it is %. So 21% oxygen means 21 parts out of a hundred, or 21 of those squares. The word is worth learning properly here, because it turns up constantly later.
The Surprise in Those Figures
Most people guess that air is mainly oxygen, since oxygen is the part we cannot do without. It is not. More than three quarters of air is nitrogen, and the gas that keeps us alive is only about a fifth of the whole.
Making a Firki
You need paper cut square at 15 cm on every side, scissors, one all-pin and a soft stick. Cut and fold it as the steps show, then pin it to the stick so it can spin freely. It takes a few minutes and it can be decorated however you like.
Making It Spin
Hold the firki and run, and it turns. Stand still and blow on it, and it turns. Move it a little back and forth and it turns again. In every case something is pushing the blades round, and that something is moving air, which is to say wind.
The Same Idea, Made Large
A windmill works the way a firki works. Wind arrives, the wings turn, and the turning can be put to use. It might run a flour mill. It might pull water up from a well. Most often now it is used to generate electricity.
Wind Farms
Put a large number of windmills together on one stretch of land and you have a wind farm, built to turn the energy of the wind into electricity. India has many. Muppandal in Tamil Nadu, Jaisalmer in Rajasthan and Brahmanvel in Maharashtra are among the leading ones.
Why Any of This Counts
Air is the first of the treasures Ajji talks about, and it makes the point about all of them. It is free, it is everywhere, it is invisible, and nothing alive lasts long without it. The wind farms show the second point: a treasure can be put to work as well as simply used.
Concepts and terms
Not a single substance. Nitrogen fills most of it, oxygen comes next, and argon with carbon dioxide and others make up the small remainder. Drawn on a hundred-square grid the split is easy to see.
The number of parts in every hundred, written with the sign %. Saying oxygen is 21% means 21 squares out of a hundred, which is how the composition picture is built.
The body needs it to carry out its functions. Hold your breath and the supply stops, which is why holding it for long grows uncomfortable so quickly. Most other living beings need it too.
Simply air on the move. Light air is a breeze; air moving hard is what blows in a storm. Being invisible, it is known by what it pushes, from a page to the wing of a windmill.
Watch out!
Myth or fact?
Case Study
Scenario:
A class reads that of every hundred parts of air, 78 are nitrogen, 21 are oxygen and 1 is everything else. Rohit says oxygen must be the main gas because we breathe it. Their teacher asks the class to draw the figures as a hundred squares, shading each gas. The picture surprises them. Oxygen fills about a fifth of the grid and nitrogen takes up more than three-quarters. Sana works out what that means. The gas we depend on most is not the gas there is most of, so how much there is and how much it matters are two different questions.
Analysis:
Drawing the hundred squares separates importance from quantity. Oxygen is a fifth of the air and nearly all of why we can breathe it.
Activity:
Draw a ten by ten grid and shade 78, 21 and 1 squares for the gases of air. Write one sentence on what surprised you.
Try it at home
Title:
Build a firki and find the wind
Safety:
An all-pin is sharp at both ends. Push it in with the flat of your thumb, keep the point away from your face, and ask an adult to help with the pinning.
What You Notice:
It will not turn in still air, which is the useful result. Every time it does turn, something was moving the air: your breath, your running, or the wind outside. A firki is a wind detector before it is a toy, and a windmill is the same detector built large enough to do work.
Did you know
Muppandal in Tamil Nadu, Jaisalmer in Rajasthan and Brahmanvel in Maharashtra hold three of the largest wind farms in the country.
A windmill can be set to run a flour mill or to draw water up from a well, not only to make electricity.
A firki is cut from a single square of paper about 15 cm across, pinned to a soft stick.
Memory tricks
The composition of air — Seventy-eight, twenty-one, one — Nitrogen, then oxygen, then everything else put together.
How long the body waits — Days for food, minutes for air — Which of the three is most urgent is settled by that one line.
Practice MCQs with answers (20)
- A a mixture of several gases
- B a kind of very light water
- C an empty space with nothing in it
- D a single pure gas
Show answer
Why:
Several gases together carry the one name.
- A 21
- B 78
- C 1
- D 50
Show answer
Why:
More than three quarters of the whole.
- A 78
- B 21
- C 1
- D 99
Show answer
Why:
About a fifth, which surprises most people.
- A I and II only
- B II and III only
- C I and III only
- D I, II and III
Show answer
Why:
I and III are correct. II is not: oxygen takes 21 parts in a hundred, and it is the remaining gases together that come to one.
- A wrong, because air holds no oxygen at all
- B right, oxygen is about 78%
- C wrong, oxygen is about a fifth and nitrogen takes most of it
- D right, because nothing else in the air is of any real use at all
Show answer
Why:
Being essential and being plentiful are different things.
- A a quantity too small to measure
- B the weight of a gas in grams
- C the speed at which air moves
- D the number of parts in every hundred
Show answer
Why:
Twenty-one per cent means 21 out of a hundred.
- A Both true, and the reason explains the assertion
- B Both true, but the reason does not explain it
- C The assertion is true and the reason is false
- D The assertion is false and the reason is true
Show answer
Why:
Both are true, and the reason is the comparison itself. Food can wait for days; air cannot wait for minutes.
- A the lungs fill up with nitrogen
- B the body is not getting the oxygen it needs
- C the chest grows tired out from all the effort
- D carbon dioxide has no way to enter
Show answer
Why:
The supply has been cut off.
- A that books cannot stay shut
- B that paper is very light
- C that air is present and moving
- D that the fan is making the pages hot
Show answer
Why:
Air is noticed by what it does.
- A vapour
- B a current of water
- C a cloud
- D wind
Show answer
Why:
Fast or slow, the name is the same.
- A a storm
- B a drizzle
- C a still afternoon
- D a mist
Show answer
Why:
Same air, very different speed.
- A the paper has become damp
- B there is no moving air to push the blades
- C firkis only turn in sunlight
- D the pin has been fixed in much too tightly
Show answer
Why:
Give it some wind and it will turn.
- A 1 metre by 1 metre
- B 5 cm by 5 cm
- C 15 cm by 15 cm
- D 50 cm by 50 cm
Show answer
Why:
Cut, folded, and pinned to a soft stick.
- A a clock that a spring drives
- B a boat that oars drive
- C a bicycle wheel that a chain drives
- D a firki that the wind pushes round
Show answer
Why:
Wind arrives, the wings turn.
- A run flour mills, lift well water, or make electricity
- B store rainwater for later use
- C clear smoke out of the sky
- D cool down the air of a whole village all through the summer
Show answer
Why:
Three quite different jobs from one turning motion.
- A a field where the crops are all grown in a very strong wind only
- B an area with many windmills, built to generate electricity
- C a single very tall windmill
- D a building that stores wind for later
Show answer
Why:
The word farm here means many of them together.
- A the gases that are found in air
- B rivers
- C leading wind farms in India
- D types of windmill
Show answer
Why:
Tamil Nadu, Rajasthan and Maharashtra in turn.
- A it is only ever present where there are some plants
- B it is found only high above the ground
- C it can be seen clearly on a bright day
- D it cannot be seen, and is known by what it moves
Show answer
Why:
Rustling, swaying, fluttering.
- A watch clothes on a line and see whether they sway
- B weigh an empty bottle on a balance
- C listen out for any sound at all coming from the air
- D look carefully at a patch of empty sky
Show answer
Why:
Look for what the air is pushing.
- A nitrogen to carry out their functions
- B carbon dioxide to carry out their functions
- C argon to carry out their functions
- D oxygen to carry out their functions
Show answer
Why:
It is the same gas we cannot do without.
Important short questions (6)
Nitrogen 78%, oxygen 21%, and 1% shared between argon, carbon dioxide and traces of several others.
The air we breathe in carries oxygen, and the body needs it to carry out its functions. Holding the breath stops that supply.
Food lasts longest, a few days. Water is shorter than that. Oxygen is the shortest of all, only a few minutes.
Watch the leaves of a tree rustle, or clothes swaying on a line. Switch a fan on and the pages of an open book lift.
Moving air pushes against its blades and spins it. A windmill works the same way, with wind turning its wings.
An area holding a large number of windmills. The energy of the wind turns them, and that is used to generate electricity.
Long answer questions (3)
Air is not one gas but a mixture. Drawn on a grid of a hundred squares, nitrogen fills 78 of them and oxygen fills 21. A single square is left for argon, carbon dioxide and the other gases together. The surprise is in the second figure. Oxygen is the part nobody can do without, so people expect it to be the bulk of the air, and it is only about a fifth. Being essential and being plentiful turn out to be two quite separate things.
A firki is a square of paper cut and folded into blades and pinned to a soft stick. Run with it, or blow on it, and it spins, because moving air is pushing against the blades. A windmill does exactly the same on a much larger scale: wind arrives and the wings turn. That turning can drive a flour mill or lift water from a well, but most often it generates electricity. Many windmills together on one stretch of land make a wind farm, and India has several large ones.
Nobody has ever seen air, so it is known entirely by what it does. Leaves rustle on a tree, clothes sway on a line, and the pages of an open book flutter once a fan is switched on. Each of those is air moving something. It matters because of what it carries. Oxygen is one of the gases in it, and the body needs oxygen to carry out its functions. A person may last some days without food, but only a few minutes without oxygen, and most other living beings are the same.
Flashcards (15)
Play this topic
- Gas, or not a gas in air?
- Term and meaning
- Fact or myth?
- From wind to electricity
- Air sprint
Water Everywhere, and Hardly Any to Use
Two-thirds of the planet is under water, and almost none of it can be drunk. The gap between how much there is and how much we can reach is what makes every drop worth saving.
What you will be able to do
- I can explain why most of the water on Earth cannot be used by us.
- I can name the forms freshwater takes and say which of them we can actually reach.
- I can list ways water is wasted at home and ways the wastage can be cut.
- I can describe rainwater harvesting and how a stepwell collects and stores water.
Key points
About two-thirds of the surface of the Earth is covered by water.
Most of that water sits in oceans and seas, and it is saline, which means salty.
Saline water will not do for homes, for farming or for industry.
Those uses need freshwater: ice sheets and snow, rivers and lakes, and water underground.
Ice, snow and underground water are all hard to get at when they are needed.
Only a tiny share of it, held in ponds, rivers, lakes and wells, can simply be reached.
Throwing trash into a river, and dumping waste from homes and industries, pollutes it.
Harvesting rain, fixing leaks and closing taps all cut the amount that is thrown away.
Full explanation
Filling the Troughs
Bhoomi and Surya help Ajji fill the water troughs for the cows, and then water the vegetables and the medicinal herbs in the garden. Ajji shows them how to do it so that every drop lands where it is wanted and none of it runs away wasted. It is a small lesson, and the whole topic is inside it.
What We Use It For
Make your own list and it grows quickly. Drinking. Cooking. Bathing. Washing clothes and utensils. Cleaning the house. Beyond the home there is more: crops will not grow without it, and industries need it in large quantities. Very little of an ordinary day happens without water somewhere in it.
How Much There Is
Water covers about two-thirds of the surface of the Earth. Seen from far enough away the planet is mostly blue. From that fact alone you would expect water to be the last thing anybody ever ran short of.
And Why That Is Misleading
Most of that water lies in the oceans and the seas, and it is saline, which simply means salty. Saline water is not fit for use in homes, on farms or in industry. The single largest store of water on the planet is of no direct use for any of the things we need water for.
Where the Usable Water Is
What those uses need is freshwater, and it is found in three sorts of place. Some is locked up as ice sheets and snow. Some runs on the surface as rivers and lies in lakes. Some is underground. Together they are a small share of the whole.
Present Is Not the Same as Reachable
Ice sheets and snow hold a great deal of freshwater, and none of it is easy to get at. Underground water is difficult to reach as well. What is left over, a very small fraction sitting in ponds, rivers, lakes and wells, is the part that can simply be taken. That fraction is what everybody lives on.
Ajji's Point, Made Properly
Now Ajji's care with the watering can looks different. Water is precious not because there is little of it but because so little of it is within reach. Nothing about the amount in the oceans changes what is available at a village tap.
Where It Goes to Waste
Go through an ordinary day and mark the places. Washing hands with the tap running. Washing clothes, washing utensils, taking a shower. Cooking, gardening, brushing teeth. For each one, ask how the water is wasted and what could be done differently. Most people are surprised by their own list.
Cutting the Waste
Some of the answers are very small habits. Turn the tap off when it is not actually being used. Get a leaking tap or pipe mended instead of living with it. Beyond habits there are two larger measures: water can be recycled, and rain can be harvested.
Spoiling What We Have
India has many rivers, streams and lakes, and plastic bags and wrappers float on far too many of them. Trash thrown into a water source pollutes it. So does waste from homes and from industries when it is dumped in. Polluted water is not fit for any living being to drink.
Not Everybody Has the Same Tap
Because freshwater sources are limited, many parts of India are short of water. In some places people walk long distances simply to fetch drinking water. Access is not shared out evenly, which is one more reason for using what there is with care.
Catching the Rain
Rainwater harvesting means collecting rain and storing it in large quantities for later use. It is done on the roofs of buildings, and in homes, housing societies and schools. It is not a new idea here. India has practised it for a very long time.
Stepwells
In Rajasthan they are called Bawadi and in Gujarat Vav. These are stepwells, built as an answer to how little water those regions get. Toorji ka Jhalra in Jodhpur is one you can still go and see. They were built for harvesting water, and the way they do it is worth understanding.
How a Stepwell Fills
A trench is dug deep into the ground and its walls are lined with blocks of stone. The stones are laid so that water can seep through them. So the well takes in rain falling on it, and also water seeping in from lakes, ponds and rivers nearby. Two supplies, into one store.
Look for Your Own
Almost every region in India has some traditional way of holding on to water, shaped by how much rain it gets and what the ground is like. Ask a teacher or a grandparent what was done locally. It is usually older, and cleverer, than anybody expects.
Concepts and terms
The salty water of the oceans and seas, which is where most of the water on Earth is. It cannot be used for drinking, for washing, for growing crops or for industry, however much of it there is.
Water that is not salty. It is found as ice sheets and snow, as rivers and lakes on the surface, and underground. Everything we do with water at home and on a farm depends on it.
Not just present, but reachable when wanted. Ice sheets hold a great deal of freshwater and are no help at all. Only a very small fraction, in ponds, rivers, lakes and wells, is easy to get at.
Catching rain where it falls and storing it in quantity for later use. Roofs of buildings, homes, housing societies and schools are all used for it, and in India the practice is an old one.
Watch out!
Myth or fact?
Case Study
Scenario:
A class is told that about two-thirds of the Earth's surface is covered by water. Imran concludes that water shortages cannot be real. Their teacher asks what kind of water that is. Most of it sits in oceans and seas and is saline. The class then subtracts: what is left is a small fraction, and much of that is frozen or deep underground. They shade a hundred-square grid to see it. The usable portion is a sliver. Imran revises his conclusion. There is a great deal of water and very little of it is the kind a town can drink, which is why shortage and abundance are both true at once.
Analysis:
Two-thirds covered and still short, because covered counts salt water. The grid is what makes the usable sliver visible.
Activity:
Shade a hundred-square grid to show salt water, frozen water and usable fresh water. Write what the smallest part means for your town.
Try it at home
Title:
Audit a week of water
Safety:
Do not climb to reach a tap or open anything under a sink. Ask an adult before moving a bucket of water, and wipe up spills so nobody slips.
What You Notice:
The dripping tap is the row that changes minds, because the figure for a whole day is always larger than anybody guesses. The habits column fills up fastest for brushing teeth and washing utensils. Compare your third column with somebody else in the class: the suggestions that work are almost always the ones that cost nothing.
Did you know
World Water Day falls on 22 March every year.
Bawadi is the name a stepwell goes by in Rajasthan, and Vav is the name it goes by in Gujarat.
The trench walls of a stepwell are lined with blocks of stone, which are laid so that water can seep through them.
Memory tricks
Why so much water is useless to us — Most is salty, most of the rest is frozen or buried — What is left over is the small part we actually live on.
Three ways to save it — Close the tap, mend the leak, catch the rain — One habit, one repair, and one thing to build.
Practice MCQs with answers (20)
- A two-thirds
- B one-tenth
- C all of it
- D one-third
Show answer
Why:
Which is why a shortage sounds unlikely.
- A rivers and lakes
- B oceans and seas
- C ice sheets
- D wells
Show answer
Why:
And that is exactly the difficulty.
- A boiling
- B frozen
- C salty
- D muddy
Show answer
Why:
The word describes ocean water.
- A anything at all on the whole surface of the Earth
- B holding fish and other sea life
- C looking at from a boat
- D domestic, agricultural and industrial purposes
Show answer
Why:
Home, farm and factory all need freshwater.
- A ice sheets and snow
- B salt pans
- C ocean currents
- D sea spray
Show answer
Why:
Rivers, lakes and underground water are the others.
- A Both true, and the reason explains the assertion
- B Both true, but the reason does not explain it
- C The assertion is true and the reason is false
- D The assertion is false and the reason is true
Show answer
Why:
Both are true, and the reason is the whole difficulty. A supply you cannot reach is no supply at all.
- A clouds high above the ground
- B ice sheets and snow
- C ponds, rivers, lakes and wells
- D the deep ocean
Show answer
Why:
And it is a very small fraction of the whole.
- A water is never ever used up by anybody at all anywhere on the whole of the planet either
- B oceans are steadily growing larger
- C the planet is not mostly water
- D nearly all of it is saline or hard to reach, so very little can actually be used
Show answer
Why:
How much exists and how much is usable are different questions.
- A wastage of water
- B water pollution
- C water recycling
- D water harvesting
Show answer
Why:
A very small habit fixes it.
- A brush more quickly
- B turn the tap off while brushing
- C use warm water instead
- D brush outside in the garden
Show answer
Why:
Running water is doing nothing at that moment.
- A closing that room entirely
- B putting a bucket under it
- C fixing the leakage
- D using the tap less often
Show answer
Why:
Repair beats working around it.
- A water recycling
- B seepage
- C water harvesting
- D water pollution
Show answer
Why:
Waste dumped from homes and industries does the same.
- A I and II only
- B II and III only
- C I and III only
- D I, II and III
Show answer
Why:
I and III are correct. II is not: saline water serves none of those purposes, which is why so little of the water on Earth is of use.
- A visit a stepwell for its beauty
- B fetch drinking water
- C reach the nearest ocean
- D collect rain as it falls
Show answer
Why:
Freshwater sources there are limited.
- A watering plants only when it rains
- B letting all of the rain run off the roofs and into the streets outside
- C collecting rainwater and storing it in large quantities for later use
- D measuring how much rain falls each year
Show answer
Why:
Homes, schools and housing societies all do it.
- A Jhalra only
- B Talab
- C Vav
- D Bawadi
Show answer
Why:
In Gujarat the same thing is called a Vav.
- A the scarcity of water in those regions
- B a shortage of building stone
- C the need for somewhere cool to sit
- D too much rain in those regions
Show answer
Why:
The building answers the climate.
- A So that the trench looks handsome to everybody passing by
- B So that water can seep in through the gaps between them
- C So that animals cannot climb down into the water below
- D So that the rain is kept out of the trench altogether
Show answer
Why:
The lining holds the trench open without sealing it. Water from the ground around goes on feeding the well between one rain and the next.
- A pipes laid by the government
- B nearby lakes, ponds and rivers
- C the sea
- D the clouds directly
Show answer
Why:
Two supplies feeding one store.
- A 5th June
- B 15th August
- C 2nd October
- D 22nd March
Show answer
Why:
Find out why the day was started.
Important short questions (6)
That water is saline, which means salty. Saline water is not fit for use in homes, in farming or in industry.
As ice sheets and snow, as rivers and lakes, and underground. Only the small amount in ponds, rivers, lakes and wells is easy to reach.
Turn taps off whenever they are not in use. Any leaking tap or pipe should be mended promptly.
By throwing trash such as plastic bags and wrappers into them. Waste from homes and from industries is dumped into them too.
Collecting rainwater and storing it in quantity for later use. It is done on buildings, and in homes, housing societies and schools.
Its trench walls are lined with stone blocks that let water through. So it takes in rain, and also seepage from lakes, ponds and rivers nearby.
Long answer questions (3)
The two statements measure different things. Most of that water lies in the oceans and the seas, and it is saline. Salty water cannot be used in homes, on farms or in industry. What those uses need is freshwater, and it is only a small share of the whole. Worse, most of that share is out of reach: some is locked into ice sheets and snow, and some lies underground. Only a very small fraction, in ponds, held in rivers, in lakes and in wells, can simply be reached. Everybody depends on that share.
A stepwell is a deep trench dug into the ground, known as a Bawadi in Rajasthan and a Vav in Gujarat. Toorji ka Jhalra in Jodhpur is one example. Those regions are short of water, and the stepwell was built as an answer to that scarcity. Its walls are lined with blocks of stone laid so that water can seep through them. Because of that lining it stores more than the rain falling on it: water also seeps in from lakes, ponds and rivers nearby. It is an age-old way of harvesting water.
Start with habits, because they cost nothing. Taps should be turned off while hands are being soaped or teeth brushed, since running water does no work at that moment. Every leaking tap and pipe should be mended, because a leak wastes water day and night with nobody using it. Then the larger measures. Water can be recycled, so that water used once is used again for a job that does not need it clean. Rain falling on the school roof can be collected and stored for later use. Finally, nothing should be thrown into the drain or the nearby pond, because polluted water is not fit for any living being.
Flashcards (15)
Play this topic
- Easy to reach, or not?
- Term and meaning
- Fact or myth?
- From all the water to your glass
- Water sprint
The Cow, the Grass and the Sun
Two children argue about where a grazing cow gets its energy. Settling that one argument properly shows why the Sun stands behind every meal anybody has ever eaten.
What you will be able to do
- I can explain why the Sun is called the main source of energy on Earth.
- I can trace the energy in a meal back to sunlight, step by step.
- I can give everyday jobs that the heat and the light of the Sun are put to.
- I can describe how a solar panel, a solar cooker and a solar water heater are used.
Key points
Every plant and animal on Earth depends on the Sun, which is the chief supplier of energy here.
Sunlight is what lets plants prepare their own food.
Animals eat plants and grow on them, and we take food from plants and animals alike.
Heat from the Sun dries chillies, clothes and cut mangoes without any fuel being burnt.
Solar panels capture the energy of the Sun and produce electricity from it.
A solar cooker uses that energy for cooking, and a solar water heater for heating water.
Panels are set on rooftops, on street lights and on traffic signals.
Standing in sunshine is not how an animal takes in energy; eating a plant is.
Full explanation
Drying Chillies
On a sunny day Bhoomi and Surya help Ajji spread chillies out to dry. Ajji explains why. The heat of the Sun takes the moisture out of them. Dried chillies can then be used later in the year, when fresh ones are not to be had. She promises them some to carry home.
A Claim Worth Testing
Then Ajji says something larger. Energy on Earth comes chiefly from the Sun, and every plant and animal here leans on it. That is a very big claim, and it is worth pulling apart rather than simply agreeing with.
The Obvious Uses First
Heat and light from the Sun get used all day without anybody noticing. Clothes dry on a line. Mangoes are cut and spread out. Grain is laid in the yard. None of it needs fuel, and none of it needs paying for. Make a list of your own and it gets long.
The Argument by the Field
One afternoon the children pass a field where a cow is grazing. Surya says the cow is getting its energy from the grass, not from the Sun. Bhoomi says the cow is getting it from the Sun. They look at the same animal and disagree completely.
Where Surya Is Right
Surya has noticed something correct. A cow standing in sunshine is not taking energy in through its back. Sunlight falling on an animal does not feed it. If that were the test, anybody could skip lunch by sitting outside.
Where Bhoomi Is Right
But follow the grass. Grass is a plant, and its leaves need sunlight in order to grow. The energy stored in that grass came from sunlight in the first place. When the cow eats it, that is where the energy has come from. Bhoomi is right about the source, and Surya is right about the route.
How Plants Do It
Sunlight helps plants prepare food. That is the step the whole argument turns on, and it is the step that makes plants different from animals. A plant makes its own food; an animal has to go and find some.
The Chain, Written Out
A plant draws energy from the Sun and makes food with it. An animal feeds on that plant and grows. Our own food comes from plants and animals alike. Every link leads back to the same place, which is why the Sun is called the main source of energy.
Your Own Breakfast
Try it on whatever you ate this morning. Rice, wheat, a vegetable: a plant grew it using sunlight. Milk or an egg: an animal made it after eating plants. There is no third possibility hiding anywhere on the plate.
Panels on a Roof
Solar panels are a common sight now: up on roofs, above street lights, and on traffic signals. They capture the energy of the Sun and produce electricity from it. Once they are in place they go on doing it every sunny day with nothing burnt.
Cooking and Heating
The energy can also be used directly, without turning it into electricity first. A solar cooker cooks food with it. A solar water heater warms water with it. Both are simply ways of catching what was arriving anyway.
A Question to Sit With
What would happen if the Sun were not visible for a few days? Lights would have to be switched on during the day, which is the answer everybody gives first. Keep going and the list gets serious. Washing would not dry, and nor would chillies. Panels would make no electricity. Plants would be short of what they need in order to grow.
A Matter of Gratitude
Across a great many homes in this country, water is offered to the Sun at first light, and it is meant as thanks. The custom is much older than any solar panel, and it rests on the same observation Ajji is making.
What the Chapter Is Doing
Air, then water, and now the Sun. Each is free, each is everywhere, and each turns out to be holding up something we could not manage without. The Sun is the one that stands behind the other treasures as well.
Settling It Properly
So who won the argument by the field? Both children did, and neither of them alone. The cow gets its energy from the grass, and the grass got its energy from the Sun. Say only the first half and you have missed where it came from. Say only the second and you cannot explain why the cow still has to eat.
Concepts and terms
Everything alive on Earth traces its energy back to the Sun. Plants use sunlight to prepare food, animals eat plants, and we eat both. No other source stands behind so much.
A cow standing in sunshine is not collecting energy from it. A cow eating grass is, because the grass needed sunlight to grow. The route matters as much as the source.
Chillies and raw mangoes are spread out to dry. Clothes on a line dry the same way. Nothing is burnt and nothing is paid for, because the heat arrives on its own.
A solar panel captures the energy of the Sun and produces electricity. A solar cooker uses the energy straight for cooking, and a solar water heater uses it to warm water.
Watch out!
Myth or fact?
Case Study
Scenario:
A class is asked where the energy in a glass of milk comes from. Most answer the cow. Their teacher asks what the cow eats, and the answer is grass. The class traces it one step further and reaches sunlight, because the grass prepares its own food using it. Nita then asks whether a person standing in the sun gets energy the same way. They work out that we cannot, because we have no way of making food from light, so our share has to arrive through a plant. The class writes the chain out and sees that every link but the first is a passenger.
Analysis:
The chain is milk, cow, grass, Sun, and only the grass can use the Sun directly. Everything after it is carried.
Activity:
Write the energy chain for two foods you ate today. Mark the plant in each chain and how many steps it is from you.
Try it at home
Title:
Trace one meal back to the Sun
Safety:
This is a paper exercise. Do not taste or handle anything raw, and wash your hands before you start writing near food.
What You Notice:
Everything gets there in the end, though some items take three or four steps. Salt and water are the rows people argue about, because neither is food that anything grew. Milk and eggs are the useful rows: they take two steps rather than one, and that extra step is exactly what the cow argument was about.
Did you know
Water is offered to the rising Sun in a great many Indian homes, by way of thanks.
Solar panels are fitted on rooftops, on top of street lights and on traffic signals.
Cut raw mangoes are spread in hot sun for several days to dry them, and dried chillies keep for the season when fresh ones are gone.
Memory tricks
The chain from the Sun to a meal — Sun, plant, animal, plate — Four steps, and the first one is where all of it begins.
Settling the cow argument — Standing in it is not eating it — The cow gets the Sun through the grass, not through its back.
Practice MCQs with answers (20)
- A the Sun
- B coal
- C running water
- D the wind
Show answer
Why:
Every plant and animal depends on it.
- A stay cool in hot weather
- B prepare their own food
- C grow thicker bark
- D lose water more quickly
Show answer
Why:
The step the whole chain turns on.
- A making its own food in the way a plant does
- B taking in energy through its back
- C not taking in energy that way at all
- D storing sunlight for use later on during the night
Show answer
Why:
Standing in it is not eating it.
- A cows can make their own food
- B the field is warm during the day
- C sunlight falls upon the cow the whole time that it eats
- D the grass it eats needed sunlight in order to grow
Show answer
Why:
Follow the grass back one step.
- A plants make food from sunlight, animals eat plants, and we eat both
- B the Sun feeds animals directly and feeds plants quite separately from that
- C food is made by the soil and handed on from there to the plants
- D animals make the food and the plants then eat them
Show answer
Why:
One starting point, several links.
- A make them hotter to taste
- B dry them so they keep for later
- C change their colour
- D keep insects away from them
Show answer
Why:
Cut raw mangoes are treated the same way.
- A a coal fire
- B a gas stove
- C clothes drying on a line
- D a kerosene lamp left burning
Show answer
Why:
The heat arrives on its own.
- A blocks sunlight from reaching the roof underneath it
- B measures how bright the Sun is at different times of the day
- C stores sunlight in a tank
- D captures the Sun's energy and produces electricity
Show answer
Why:
Rooftops, street lights and traffic signals carry them.
- A rooftops, street lights and traffic signals
- B the floors of buildings
- C the walls of wells
- D the underside of all the road bridges around
Show answer
Why:
Wherever they can face the sky.
- A after turning it into electricity first
- B directly, for cooking food
- C to keep food cold
- D only to dry food out
Show answer
Why:
No fuel of any kind is needed.
- A pump water up from a well
- B produce electricity for a house
- C heat up water for the house
- D purify water for drinking
Show answer
Why:
Another direct use of the same energy.
- A right, because every last bit of energy anywhere begins at the Sun
- B wrong, because sunlight does not carry any energy at all
- C right, because sunlight warms her
- D wrong, because animals get the Sun's energy by eating plants
Show answer
Why:
The source is right, the route is not.
- A I and II only
- B II and III only
- C I and III only
- D I, II and III
Show answer
Why:
I and III are correct. II is not: a cow standing in the Sun all afternoon has eaten nothing and taken in no energy at all.
- A the rivers would all run completely dry straight away
- B artificial lighting would be needed during the day
- C the wind would stop blowing
- D all soil would turn to rock
Show answer
Why:
Keep going and the list gets more serious.
- A keeping every window shut tight all the day long
- B lighting a lamp at midnight
- C offering water to the Sun early in the morning
- D planting a tree every year
Show answer
Why:
A custom much older than any solar panel.
- A milk holds a little sunlight inside it directly
- B cows are given water that has been warmed by the Sun all day
- C milk is warmed by sunlight
- D the animal that made it grew on plants that used sunlight
Show answer
Why:
There is no third route onto the plate.
- A sunlight, plant, animal, our food
- B plant, Sun, our food, animal
- C our food, animal, plant, Sun
- D animal, Sun, plant, food
Show answer
Why:
Everything leads back to the same place.
- A Both true, and the reason explains the assertion
- B Both true, but the reason does not explain it
- C The assertion is true and the reason is false
- D The assertion is false and the reason is true
Show answer
Why:
Both are true, and the reason is how the cooker works. Nothing is lit, so nothing is used up.
- A a hand pump at a well
- B a solar panel on a roof
- C a coal-fired stove
- D a torch running on cells
Show answer
Why:
It has nothing to capture.
- A electricity from a panel
- B wind rather than the Sun
- C light from the Sun to make food
- D heat from the Sun to remove moisture
Show answer
Why:
The same method dries the chillies.
Important short questions (6)
Plants use its light to prepare food. Animals eat those plants, and we eat both plants and animals. Every link leads back to it.
It eats grass. Grass leaves need sunlight in order to grow, so the energy stored in the grass began as sunlight.
Chillies and cut raw mangoes are spread out to dry. Washed clothes are hung on a line and dry the same way.
It captures energy from the Sun and produces electricity. Panels are fitted on rooftops, street lights and traffic signals.
A solar cooker, which cooks food with it. A solar water heater, which uses it to warm water.
Sunlight falling on an animal does not feed it. Animals take in the energy of the Sun by eating plants that grew using sunlight.
Long answer questions (3)
Both of them have hold of something true. The one who says the cow is not taking energy in from the sunshine is right about that. Sunlight falling on an animal does not feed it, and no animal can live by standing outside. But the other is right about where the energy started. The cow eats grass, and grass is a plant whose leaves needed sunlight in order to grow. So the energy in that grass came from the Sun. The cow gets it through the grass, not through its back. One child had the route and the other had the source.
Some uses need no equipment at all. Chillies and cut raw mangoes are spread out to dry in the heat. Washing dries on a line the same way. Nothing is burnt and nothing is paid for. Then there are devices. A solar panel captures the energy of the Sun and produces electricity, and panels sit on rooftops, on street lights and on traffic signals. A solar cooker uses the energy straight, for cooking. A solar water heater uses it to warm water. All of them are simply ways of catching what was arriving anyway.
Take any part of the meal. Rice, wheat or a vegetable was grown by a plant, and that plant prepared its food using sunlight. Milk, curd or an egg came from an animal, and that animal grew by eating plants. Those plants needed sunlight too. There is no third route onto a plate, because nothing on it makes its own energy from nowhere. A plant draws energy from the Sun and makes food. An animal feeds on plants and grows. Our food comes from both, which is why the Sun is called the chief supplier of energy here.
Flashcards (15)
Play this topic
- Does it use the Sun?
- Device and job
- Fact or myth?
- From sunlight to your plate
- Solar sprint
Forests, Soil and the Rock Underneath
Fallen leaves feed the soil that grows the next tree, and the soil itself came from rock broken down over thousands of years. Everything here is slow, and that is the point.
What you will be able to do
- I can explain what a forest gives us and why the forest cover is shrinking.
- I can describe the recycling that goes on between fallen leaves, soil and new plants.
- I can explain how soil is formed and say what can be found inside a handful of it.
- I can give uses of rocks and minerals, and name some of each.
Key points
Forests are large areas carrying a dense growth of many kinds of plants.
They are a natural home for wild animals, birds and insects, giving food and shelter.
Forest cover has been shrinking, mainly through large scale cutting of trees by people.
Growing a new forest, or restoring a lost one, takes many years.
Roots hold the soil in place, and fallen leaves decay and enrich it for the next plant.
Soil is formed as rock is broken apart by the Sun, water and living organisms.
That breaking apart is slow, and takes thousands of years to produce soil.
Minerals make up the rocks, and aluminium, gold, copper and iron are drawn out of minerals.
Full explanation
A Walk Into the Forest
Ajji takes Bhoomi and Surya out for a morning walk in the forest. They find herbs, shrubs and trees of many kinds growing close together. Ajji gives them the definition as they walk. A forest is a wide stretch of land packed thickly with plants of many kinds.
The Gooseberries on the Ground
They gather some nellikai, the Kannada name for Indian gooseberries, that have fallen. Ajji explains the village rule. Fruit is not plucked from the trees. What has fallen may be collected, and the rest is left for the animals and the birds.
What a Forest Gives
Make a list of products that come out of a forest and it gets long quickly. Beyond that, a forest is where a great many wild creatures live naturally, birds and insects among them, and it feeds them and shelters them. Every animal there depends on other life forms to live.
Diversity Has a Job
The range of life forms in a forest is not decoration. It is what makes sure there is food for every living being in it. Take enough of that variety away and the arrangement stops working for the ones left behind.
The Cover Is Shrinking
Year on year the country has been losing forest, and what people do is behind it, above all the felling of trees on a large scale. The difficulty is the timescale. Growing a new forest, or restoring one that has been lost, takes many years. So forests have to be used responsibly, with enough time left for them to regenerate.
People Who Stood in the Way
India has an old tradition of respecting and protecting forests, sacred groves among them. The Chipko movement is the famous modern example. It began in the early 1970s in Uttarakhand, then part of Uttar Pradesh. Local women took an active part, encircling and hugging the trees so that they could not be felled.
A Festival for Planting
Van Mahotsav runs for a week every July, across the country. New plants and trees go into the ground and awareness of forests is raised. The aim is to increase the green cover, and there is nothing stopping a class from organising one locally.
Damp Ground and Fallen Leaves
Walking back, the children notice how many leaves are lying on the ground and how damp the soil feels. Ajji explains both. Plant roots grip the soil, which is what keeps rain from carrying it off. The fallen leaves decay and enrich the soil with nutrients.
Recycling, Without the Word
Fresh plants and trees then grow in that soil. Nothing was carried in and nothing was taken away. Ajji calls it an example of recycling in nature, and it is happening under every tree in the forest at once.
Digging the Garden
Back at the house they help prepare the garden soil for vegetables. Ajji has them dig gently and break up the lumps. The reason is one they already know: the spaces between soil particles hold the air a seed needs, and give the roots room to push through.
What Is Actually in Soil
Bhoomi and Surya spot small pebbles, plant roots, and a few earthworms. Earthworms are natural agents that turn and loosen the soil as they go. There is sand in it, and insects, and many small organisms too small for the naked eye to pick out.
Soil Samples Side by Side
Collect soil from several places around home and school and compare them. Note the colour of each and feel the texture. Look with the naked eye, then again through a magnifying lens. Samples from different places often differ in colour, because they contain different materials.
Where Soil Comes From
Soil is formed by the disintegration of rocks, which simply means their breaking apart. The Sun does some of that work, water does some, and living organisms do some. It is not quick. The process runs over thousands of years.
Rocks at Work
Rock goes into houses and larger buildings, into temples, into roads and dams, and into the tops of tables. Slate is laid across roofs, and laterite serves for building much as a brick does. Granite, sandstone and marble are among the important ones. People have been making hand axes and arrowheads from rock for thousands of years.
What Rocks Are Made Of
Minerals are what they consist of. Aluminium, gold, copper and iron all get drawn out of minerals, which go on to serve in aeroplanes, in cars, in jewellery, in cosmetics and in electrical goods. Even a plain mobile phone holds about a dozen of them, gold and silver and copper and cobalt among them. Rocks take thousands to millions of years to form, so they too have to be used with care.
Concepts and terms
Leaves fall from the trees, decay on the ground, and enrich the soil with nutrients. New plants and trees then use that soil to grow. Nothing is brought in and nothing is thrown away.
Rock is broken apart by the action of the Sun, of water, and of living organisms. The word for that breaking apart is disintegration, and it takes thousands of years to make soil.
Minerals are what rocks consist of. Aluminium, gold, copper and iron are all drawn out of minerals, which go on to serve in aircraft, cars, jewellery, cosmetics and electronics.
Soil takes thousands of years to form and rocks take thousands to millions. Anything used faster than it forms will run short, which is the argument for using both responsibly.
Watch out!
Myth or fact?
Case Study
Scenario:
A class discusses a plan to clear a patch of forest for a car park. Arjun says a few trees are a small price. Their teacher asks the class to list everything the patch currently provides. Shelter and food for birds, insects and animals, roots that hold the soil, shade, and fallen leaves that feed the soil beneath. The list runs to eleven items. The class then asks which of them a car park also provides, and the answer is none. Arjun changes his position. He had been counting the trees, and the cost turns out to be everything the trees were supporting.
Analysis:
Counting trees undercounts a forest. The patch was doing eleven jobs and only one of them was being visible.
Activity:
Pick a green patch near you and list everything it provides. Write what would be lost if it became a road.
Try it at home
Title:
Three soils, side by side
Safety:
Do not take soil from a drain or from anywhere with garbage in it, because that soil can carry germs. Wash your hands thoroughly with soap afterwards, and do not put your hands near your face while you are working.
What You Notice:
The lens column is always longer than the naked eye column, and that gap is the finding. Roots, sand grains and small pebbles turn up in almost every sample. Colour is where the three usually differ most, and the reason is that they contain different materials. If one sample has an earthworm in it, that is the sample from the richest ground.
Did you know
The Chipko movement began in the early 1970s in Uttarakhand, and local women encircled and hugged trees to stop them being felled.
Van Mahotsav is a week-long forest festival held across the country in July, when new plants and trees are planted.
A basic mobile phone contains about a dozen minerals, among them gold, silver, copper and cobalt.
Memory tricks
What makes soil out of rock — Sun, water, living things, and a very long wait — Three agents doing the breaking, and time doing the rest.
The forest floor cycle — Leaf falls, soil gains, plant grows — Three steps, and then it starts over.
Practice MCQs with answers (20)
- A a wide stretch of land packed thickly with plants of many kinds
- B a garden that nobody looks after
- C a stretch of open grassland with just a few scattered trees on it
- D a field of one single crop
Show answer
Why:
Herbs, shrubs and trees all together.
- A shelter only
- B food and shelter
- C food only
- D nothing they could not find elsewhere
Show answer
Why:
A natural home means both.
- A the soil becoming far too rich for any trees to grow in
- B heavier rainfall in recent years
- C human activities such as large scale cutting of trees
- D animals eating too many young plants
Show answer
Why:
The cause is not a natural one.
- A Both true, and the reason explains the assertion
- B Both true, but the reason does not explain it
- C The assertion is true and the reason is false
- D The assertion is false and the reason is true
Show answer
Why:
Both are true, and the reason is her whole point. The forest is not there only for us to pick from.
- A the Chipko movement
- B a sacred grove
- C rainwater harvesting
- D Van Mahotsav
Show answer
Why:
It began in the early 1970s.
- A a kind of forest soil
- B a week-long forest festival held in July
- C a rock used for building
- D a method used for watering the young trees
Show answer
Why:
New plants and trees go into the ground.
- A they dry it out completely
- B they make it darker in colour
- C they grip it and keep the rain from carrying it off
- D they break it all up into very much smaller pieces indeed
Show answer
Why:
A second job besides taking up water.
- A stop any new plants at all from growing there
- B have to be swept away by somebody
- C make the soil poorer over time
- D decay and enrich the soil with nutrients
Show answer
Why:
New plants then grow in that soil.
- A I and II only
- B II and III only
- C I and III only
- D I, II and III
Show answer
Why:
I and III are correct. II is the opposite: the leaves decay where they fall and enrich the soil with nutrients.
- A leaves falling onto bare ground
- B the disintegration of rocks
- C rain collecting in low places
- D earthworms making new material
Show answer
Why:
Sun, water and living organisms do the breaking.
- A a single year
- B a few days
- C thousands of years
- D about one season
Show answer
Why:
Which is why soil cannot simply be replaced.
- A water
- B all of the living organisms here
- C the Sun
- D electricity carried in wires
Show answer
Why:
Three agents, working very slowly.
- A the spaces hold air and let roots push through
- B the lumps stop any of the water from leaving at all
- C digging kills the earthworms
- D loose soil looks tidier
Show answer
Why:
A point they met in an earlier chapter.
- A eat the insects living in it
- B turn and loosen it as they move
- C bring rainwater up from below
- D stop roots from spreading too far
Show answer
Why:
Natural agents doing a gardener's work.
- A have different amounts of rain on them
- B were collected at different times of day
- C contain different materials
- D were dug to different depths only
Show answer
Why:
Compare the texture as well.
- A fossil fuels
- B nutrients from leaves
- C soil
- D minerals
Show answer
Why:
And metals are extracted from those.
- A copper
- B paper
- C cotton
- D plastic
Show answer
Why:
Aluminium, gold and iron are three others.
- A making jewellery
- B roofing houses
- C building roads only
- D growing crops
Show answer
Why:
Laterite is used in the way bricks are.
- A That rock served for decoration and for nothing else at all
- B That rock was used only where no metal could be found
- C That rock has been used for tools only in the last century
- D That people have made tools from rock for thousands of years
Show answer
Why:
Stone tools turn up in the oldest layers archaeologists dig. Rock was being worked long before any metal was known.
- A no minerals at all
- B a hundred minerals
- C one mineral
- D a dozen minerals
Show answer
Why:
Gold, silver, copper and cobalt among them.
Important short questions (6)
A wide stretch of land packed thickly with plants of many kinds. Wild animals, birds and insects live there naturally, fed and sheltered by it.
The cover is already shrinking through large scale cutting. A new forest, or a restored one, takes many years to grow.
Leaves fall and decay, enriching the soil with nutrients. New plants and trees then use that soil to grow.
Rocks are broken apart by the Sun, by water and by living organisms. The process runs over thousands of years.
Sand, small pebbles and pieces of root. Insects, worms and organisms too small for the naked eye are there too.
Minerals are what rocks consist of. Aluminium, gold, copper and iron are all drawn out of them.
Long answer questions (3)
Start with what is lying on the ground. Leaves fall from the trees in large numbers, and there they decay. As they decay they enrich the soil with nutrients. New plants and trees then use that soil to grow, and in time they drop their own leaves. Nothing has been carried in from outside and nothing has been taken away, which is why it is called recycling in nature. The roots do a separate job. They grip the soil and keep the rain from carrying it off, so the enriched soil stays where the next plant needs it.
Soil begins as rock. The Sun, water and living organisms break that rock apart, a process called disintegration. It is extremely slow, running over thousands of years, and what finally results is soil. Different places end up with different soils, some good for growing certain crops and some good for making bricks. That slowness is the reason for protecting it. Anything used faster than it forms will run short, and nothing anybody does can hurry the making of soil. A forest holds a variety of soils, and it supports a great range of living things.
Rock goes into houses and larger buildings, into temples, into roads and dams, and into the tops of tables. Slate is laid across roofs and laterite serves much as a brick does, while granite, sandstone and marble are among the important ones. People have shaped rock into hand axes and arrowheads for thousands of years. Minerals are what rock itself consists of, and out of those come aluminium, gold, copper and iron. Minerals go into aeroplanes, cars, jewellery, cosmetics and electronics, and a basic phone holds about a dozen. Rocks take thousands to millions of years to form, so they must be conserved and used responsibly.
Flashcards (15)
Play this topic
- Rock, mineral, or neither?
- Term and meaning
- Fact or myth?
- From rock to a growing plant
- Soil and rock sprint
Fuels That Run Out, and Ones That Do Not
Petrol, coal and natural gas took millions of years to form and will be gone in far less. Sorting resources by how fast nature replaces them is what the last section of this chapter is for.
What you will be able to do
- I can name the fossil fuels and explain how they were formed.
- I can explain why fossil fuels will run short and what burning them does to the air.
- I can tell a natural resource from a human-made one.
- I can sort resources into renewable and non-renewable, and justify each choice.
Key points
Petrol, diesel and kerosene are all obtained from petroleum.
Petroleum, natural gas and coal together are called fossil fuels.
They grew out of the remains of tiny organisms and of plants, buried far below ground.
Forming them took millions of years, and they are found in limited quantities.
Burning them produces smoke and carbon dioxide, which pollutes the air.
Resources we get from nature are natural resources; those we build are human-made.
A renewable resource is one nature makes good again inside a span worth waiting through.
Non-renewable resources are limited, and once used they are gone for a very long time.
Full explanation
A Question at the Fuel Station
Bhoomi and Surya pass a fuel station and Bhoomi asks why different vehicles pull up at different pumps. Surya has the answer. They do not all run on the same fuel. Petrol and diesel are two, and there are others.
A Survey Worth Doing
Take a notebook into your own neighbourhood and record what you see. Which types of vehicles are there, and what fuel does each one use? A simple two-column table is enough, and the pattern in it will be clear before you have filled twenty rows.
The Two Commonest
For vehicles, petrol and diesel are the two in widest use by far. Along with kerosene, both of them are obtained from petroleum, which is why one raw material stands behind so much of what moves on the roads.
The Family Name
Petroleum, natural gas and coal are grouped together and called fossil fuels. The name is not about how they are used but about where they came from, and that is the more interesting question.
Where They Came From
Each grew out of the remains of tiny organisms and of plants that ended up buried far below ground. Over an enormous stretch of time those remains were converted into petroleum, natural gas and coal. How long? Millions of years for each of them.
The Other Two, at Work
Natural gas is used for cooking and for generating electricity, and in compressed form, as CNG, it runs vehicles, burning cleaner than either petrol or diesel. Coal goes mostly into making electricity, and several parts of India have it.
The Arithmetic Nobody Likes
Fossil fuels are found in limited quantities. Go on using them the way we do now and we will run out of them. That is the whole argument for looking at alternate sources of energy, and it does not depend on anybody being fond of the environment.
And What Burning Them Does
Set a fossil fuel alight and what comes off it is smoke together with carbon dioxide, and the air is fouled by both. Depending on them so heavily for transport and for cooking has caused large scale air pollution. So there are two separate problems: the supply, and the smoke.
Doing Our Bit
Walk or cycle to places that are near. Use public transport, which carries many people on one engine rather than one person on each. Both cut the fuel burnt without anybody having to invent anything new.
Naming the Whole Category
Everything the chapter has dealt with fills a need. Heat and light come from the Sun, water comes from rivers, food comes from plants and animals. Resources we get from nature like this are called natural resources.
And the Other Category
We also make things from those resources to suit ourselves. Electric bulbs. Furniture. Solar panels. Bicycles. Anything people have created in that way carries the name human-made resource. The materials still came from nature; the arrangement did not.
The Division That Matters
A natural process puts some of these resources back as time passes, and leaves others untouched. That single difference sorts the whole list into two, and it is the last idea in the chapter.
Why Only Fallen Nellikai
Ajji's rule turns out to be an example. Leaving fruit on the tree means enough for the animals and birds, and seeds in their droppings let new trees grow. It takes some years before those trees fruit, but the supply comes back. Whatever nature makes good again inside a span worth waiting through is called a renewable resource. Air is one, and so are water and forests.
The Other Half of the List
Making a fossil fuel runs over millions of years. Only so much of it exists, and what gets used is gone. Nothing puts any back inside a span worth waiting through. These are non-renewable resources, and minerals, rocks and soil belong on that side, along with coal, petroleum and natural gas.
The Drive Back Into the City
On the way home the children notice the skyline change colour and the air begin to smell. There are very few trees and they can smell smoke from the vehicles. Amma explains that burning fossil fuels in vehicles generates that smoke, and points out the electric ones, which release none. Effort is going into building alternatives, and the list of what we use every day is where each of us gets to start.
Concepts and terms
Petroleum, natural gas and coal. Each grew out of the remains of tiny organisms and of plants that ended up buried far below ground, and the making ran over millions of years.
What we get from nature is a natural resource. The Sun gives heat and light, rivers give water, plants and animals give food. What people build from those, such as bulbs, furniture and bicycles, is human-made.
Whatever nature makes good again inside a span worth waiting through. Air, water and forests are examples. Nature renews them, which is not the same as saying they cannot be spoilt.
Those found in limited quantities that get exhausted once used, because nothing puts any back inside a span worth waiting through. The examples are minerals, rocks and soil, along with coal, petroleum and natural gas.
Watch out!
Myth or fact?
Try it at home
Title:
Sort one day into two columns
Safety:
This is a paper exercise. Do not open gas cylinders, touch fuel of any kind, or go near a vehicle engine to check what it runs on. Ask an adult instead.
What You Notice:
The indirectly column is where the surprise sits. A bus ride looks like one resource and turns out to involve petroleum, minerals and rubber. Almost every N row traces back to something that took millions of years to form. Compare totals with a friend and the lists differ, but the balance between R and N usually does not.
Case study: the generator behind the new school block
Scenario:
A school has added a new block, and the power supply to it fails most afternoons. The head teacher has money for one thing only and three suggestions on the table. The clerk wants a diesel generator, because it works the moment it is switched on and everybody understands it. A science teacher wants solar panels on the roof of the new block, though they cost more at the start and do nothing after dark. A parent who runs a workshop wants the school to find out first what is actually using the electricity. The answer, she says, may be that nothing needs buying. The block sits beside the playground, and the classrooms have windows on two sides. The head teacher asks the class to advise her.
Analysis:
Each suggestion is answering a different question, and only one of the three asks what the problem actually is before spending anything on it.
Activity:
Spend one afternoon in your own classroom with a notebook. Every fifteen minutes, write down how many lights and fans are on, and whether the daylight coming through the windows would have been enough without them. At the end, work out for how many of those readings something was running that nobody needed. Take the figure to your class teacher with one suggestion attached.
Did you know
Coal, wood and dung cakes were once the usual cooking fuels, and natural gas and LPG have gradually replaced them.
CNG stands for Compressed Natural Gas, and it is a cleaner fuel for vehicles than petrol or diesel.
Electric vehicles release no smoke at all, which is why they are part of the answer to city air pollution.
Memory tricks
What counts as a fossil fuel — Coal, petroleum, natural gas — Three of them, all made from buried remains over millions of years.
The renewable test — Does nature replace it while we wait? — If yes it is renewable. If it takes millions of years, it is not.
Practice MCQs with answers (20)
- A petroleum
- B natural gas
- C wood
- D coal
Show answer
Why:
One raw material standing behind three fuels.
- A wood, dung cakes and charcoal
- B petroleum, natural gas and coal
- C petrol, diesel and kerosene
- D air, water and forests
Show answer
Why:
The name is about where they came from.
- A the ash that gets left behind after the big forest fires burn out
- B rocks slowly breaking apart
- C remains of tiny organisms and of plants buried far below ground
- D seawater drying up over time
Show answer
Why:
Then converted over an enormous stretch of time.
- A a few seasons
- B about a century
- C days
- D millions of years
Show answer
Why:
Formed slowly, burnt quickly.
- A wrong, it took millions of years and is limited
- B right, because oil wells refill themselves
- C wrong, because petrol is not a fuel
- D right, petrol forms every year
Show answer
Why:
The rate of forming is the whole difficulty.
- A only water vapour
- B smoke and carbon dioxide, which pollute the air
- C nothing whatever at all that ever leaves the engine
- D oxygen for the surrounding air
Show answer
Why:
A second problem, on top of the supply.
- A Combined Nitrogen Gas
- B Clean Natural Grade
- C Compressed Natural Gas
- D Coal and Natural Gas
Show answer
Why:
A cleaner vehicle fuel than petrol or diesel.
- A running aeroplanes
- B making jewellery
- C cooking in most homes
- D producing electricity
Show answer
Why:
It is found in several parts of the country.
- A water in a river
- B a bicycle
- C a wooden chair
- D an electric bulb
Show answer
Why:
We get it from nature rather than making it.
- A sunlight
- B a solar panel
- C a forest
- D coal underground
Show answer
Why:
The materials came from nature; the arrangement did not.
- A were made by human beings
- B can never be used up by anybody
- C nature makes good again inside a span worth waiting through
- D are only ever found in extremely small quantities anywhere at all
Show answer
Why:
Nature replaces them while we wait.
- A minerals, soil and rocks
- B petrol, diesel and kerosene
- C coal, petroleum and natural gas
- D air, water and forests
Show answer
Why:
Nature renews all three of them.
- A coal, petroleum and natural gas
- B sunlight, wind and rain
- C bulbs, furniture and bicycles
- D air, water and forests
Show answer
Why:
Minerals, soil and rocks belong there too.
- A there is very little of it anywhere
- B it takes thousands of years to form
- C it is made by human beings
- D nobody ever uses it up
Show answer
Why:
Too slow to be replaced in any useful time.
- A Both true, and the reason explains the assertion
- B Both true, but the reason does not explain it
- C The assertion is true and the reason is false
- D The assertion is false and the reason is true
Show answer
Why:
Both are true, and the reason is the arithmetic of it. Nothing that takes millions of years to make can be replaced in a lifetime.
- A keeping all of the vehicles running while they are parked
- B buying more vehicles per family
- C driving faster and braking less
- D walking or cycling nearby, and using public transport
Show answer
Why:
Neither needs anything new to be invented.
- A runs only on diesel
- B burns coal inside the engine
- C releases no smoke
- D uses more petrol than a car
Show answer
Why:
Part of the answer, not the whole of it.
- A cooking fires in every house
- B fossil fuels being burnt in vehicles
- C the wind blowing in from a forest
- D water being wasted at taps
Show answer
Why:
There are very few trees there as well.
- A I and II only
- B II and III only
- C I and III only
- D I, II and III
Show answer
Why:
I and III are correct. II is not: a panel is built by people out of other materials, which makes it a human-made resource.
- A Nobody knows how to use fossil fuels properly yet
- B Fossil fuels are far too expensive for anybody to buy
- C Fossil fuels are difficult to burn in an ordinary stove
- D Fossil fuels are limited and will one day be used up
Show answer
Why:
The stock underground is fixed and nothing is adding to it. What is burnt today is simply gone.
Important short questions (6)
Petroleum, natural gas and coal. They formed from the remains of microorganisms and plants buried deep inside the earth.
Fossil fuels are found in limited quantities. Used at the present rate they will soon run out, and they took millions of years to form.
Smoke and carbon dioxide gas are produced, and both pollute the air. Depending on them so heavily has caused large scale air pollution.
A natural resource comes from nature, such as water in a river. A human-made one is created by people, such as a bicycle.
Whatever nature makes good again inside a span worth waiting through. Air and forests are two of them.
All of them take far too long to form. They are limited, and nothing puts any back inside a span worth waiting through, so they count as non-renewable.
Long answer questions (3)
Petroleum, natural gas and coal are the fossil fuels, and petrol, diesel and kerosene all come out of petroleum. Each grew out of remains of tiny organisms and of plants that ended up buried far below ground, and the process ran over millions of years. The first problem is supply. They are found in limited quantities, so used at the present rate they will run out, and nothing replaces them in any useful time. The second is pollution. Burning them produces smoke and carbon dioxide, and depending on them so heavily has caused large scale air pollution.
The test is whether nature puts the resource back inside a span worth waiting through. Whatever it makes good again in that sort of time is called renewable. Air, water and forests are the usual examples. A forest shows how it works. Fruit left for animals and birds ends up as seeds in their droppings, and new trees grow, though it takes some years. Non-renewable resources are found in limited quantities and get exhausted once used, because nothing replaces them quickly enough. Minerals and rocks and soil, and coal, petroleum and natural gas, all belong on that side.
Two things differ between the places. The city has very few trees, and it has a great many vehicles burning fossil fuels. Burning those fuels produces smoke and carbon dioxide, and over-dependence on them for transport and for cooking has caused large scale air pollution. Several things help. Walking or cycling to nearby places burns no fuel at all. Public transport carries many people on one engine. Cleaner fuels such as CNG replace dirtier ones, and electric vehicles release no smoke. Planting and protecting trees deals with the other half of the difference.
Flashcards (15)
Play this topic
- Renewable or non-renewable?
- Term and meaning
- Fact or myth?
- How a fossil fuel came to be
- Resources sprint
Class 6 Science Chapter 11 — frequently asked questions
Nitrogen 78%, oxygen 21%, and 1% shared between argon, carbon dioxide and traces of several others.
The air we breathe in carries oxygen, and the body needs it to carry out its functions. Holding the breath stops that supply.
Food lasts longest, a few days. Water is shorter than that. Oxygen is the shortest of all, only a few minutes.
That water is saline, which means salty. Saline water is not fit for use in homes, in farming or in industry.
As ice sheets and snow, as rivers and lakes, and underground. Only the small amount in ponds, rivers, lakes and wells is easy to reach.
Turn taps off whenever they are not in use. Any leaking tap or pipe should be mended promptly.
Plants use its light to prepare food. Animals eat those plants, and we eat both plants and animals. Every link leads back to it.
It eats grass. Grass leaves need sunlight in order to grow, so the energy stored in the grass began as sunlight.
Chillies and cut raw mangoes are spread out to dry. Washed clothes are hung on a line and dry the same way.
A wide stretch of land packed thickly with plants of many kinds. Wild animals, birds and insects live there naturally, fed and sheltered by it.
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