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When we think it out we can see that most of the energy we use comes from the sun by way of the materials which plants build up in photosynthesis.

Scientist know only a little, so far, about photosynthesis.

It is only a little more than a hundred years since the first account of it was given by the German scientist von Mayer.

But with more experimenting being done every year, much more will certainly be known before very long.

The rate at which scientific knowledge is increasing is going up all the time.

In time it may even be possible to use the energy of light itself in industry to do in our factories something like what plants do in their green cells.

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Before long, we may learn from working on photosynthesis how to make or grow more food.

AS we have seen more than one billion people on this planet are short of food.

As more and more people are born, the need for new food supplies will increase.

It may be that we can find what we want in the sea.

It is thought that as much as 90 per cent of the photosynthesis which takes place in the world goes on in microscopic water plants in the sea.

Maybe much of the food people are going to need in the future will come out of the oceans.

Or making food straight from complexes of carbon, hydrogen and oxygen may become a great new industry.

At present we have to get most of the energy used in industry by burning coal and oil and other fuels.

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This energy is the sun's energy stored up long ago by plants.

Coal comes from the dead bodies of plants stored, away form the air and under pressure, through millions of years in great beds in the earth.

The amount of coal and oil in the earth is, it is true,very great,but the amount we are using today is great too.

A time may come before long when we will have used up all the coal and oil that is easy to get at.

We have been taking oil out of the earth only since about 1860.

Without oil there would be no cars and no airplanes.

It is strange to think that airplanes depend on what plants were doing millions of years ago.

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Plants and animals all need air.

Only about one fifth of the air is oxygen.

The other four fifths is another gas, without taste, smell or color, named nitrogen.

Both plants and animals need nitrogen as well as oxygen but they cannot take it from the air themselves.

How do they get their supply of nitrogen?

There are very small organisms in soil and water which can take nitrogen out of the air and fix it in complex materials which plants and animals can use.

These materials are taken up by plants through their roots in water from the soil.

Animals get their nitrogen by eating plants.

Some of this nitrogen comes away in animal waste and people have for many thousands of years known enough to put animal waster back into the soil to help plants grow.

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Nitrogen, like carbon,oxygen and hydrogen, is used over and over again in support of life.

Plants build nitrogen up into complex structures.

Animals eat the plants.

Then animal waste and dead plants and fallen leaves are broken down into simpler forms again.

So the great round goes on without end, all made possible only by energy coming from the sun.

Scientists say that all the oxygen and all the carbon dioxide now in the air have been put there after use by plants through photosynthesis.

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All organisms, it is clear, have a number of needs in common, of which air, water, food and the sun's light and heat are the chief.

But people have many other needs,though we may not think of them as needs.

One of them,our need for other people,is very important.

First of all, we need other people to do things for us when we are very young or very old, or when we are ill.

We need others to take care of us.

We need their help.

We need them to do things for us which we cannot do for ourselves.

We need their love.

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Every hour of our lives we do things that are possible only because of work which is done for us by other people.

Who grew the cotton?

Who made the sheets?

What watched the sheep?

Who washed the wool?

Who made the blankets for the bed you sleep in?

Whose work are you using when you turn on the light?

Who mined the coal which gives the power to heat and light your room?

But equally men and women need to do things for other people.

Most people are not happy if they are not in some way helping others-doing things for others.

They need someone to love.

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All our lives we need other people.

In many parts of the world families do everything for themselves.

Until the nineteenth century this was true almost everywhere outside the cities.

Families were self-supporting.

They grew the food they needed,

built their own houses,

and made their own clothing and furniture,

the candles for lighting the rooms at night,

and the plows and carts for work on the farm by day...

In every way they took care of themselves.

Living like this, a family is very like a simple organism.

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But a family living in a city today is more like a cell in a complex organism.

Other people whom it does not know do almost everything for it.

Workers in factories make the things it needs and send them to the stores,which sell them to it.

Other people teach its children in schools and take care of them in hospital when they are ill.

Police and fire stations keep watch over the city.

Lighting and water supplies, the clearing away of waste, the upkeep of streets and roads are all public services.

In exchange for all this, each of us does our own sort of work, our daily round, whatever it is.

This is true for most of us,if not all.

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People need play as well as work, though,if your interest is deep enough, work and play can be the same thing.

To some people all their best work is a sort of play.

They get so much pleasure form it and are so interested in it that they work when they don't need to.

They are doing what they want most to do.

It was the philosopher Plato who said,

All learning is best done as play.

Nothing learned under pressure takes root rightly in the mind.

So let children's work be a sort of play.