Original subtitles

'It's nearly summer

'and the garden is bursting with life.

'As a botanist, I'm fascinated by what makes plants grow.

'For instance, to produce all this colour and diversity

'you need just a few minerals and three basic ingredients.'

Water, sunlight and carbon dioxide,

the stuff that I'm breathing out right now.

And that is all. Nothing else.

Plants turn these ingredients into food for growth and a waste product we find very useful - oxygen.

It sounds simple,

but this process is one of the most fascinating and complicated in the whole of science.

It's called photosynthesis.

'It'll take the pioneers of botany over 400 years to work out

'why a leaf needs sunlight,

'what role water plays

'and why a plant can't exist without carbon dioxide.

'Today photosynthesis is at the forefront of scientific research.'

If we get this right and learn from photosynthesis,

we should be able to produce very quickly a liquid fuel for cars... No more gasoline, no more diesel?

No more fossil fuel.

'Photosynthesis is taking place right now in every leaf of every plant.'

I find that amazing.

'The University of Oxford Botanic Garden is the oldest in Britain.

'I've been Director here for 22 years

'and one of the great things about the job

'is that I get to live here.'

When the gates are locked, this enchanting place becomes my back garden.

It took botanists a long time to understand the complex process

that transforms a seed into a fully-grown tree.

Any scientific journey will have twists and turns. Working out how plants grow was no exception.

This is the 1648 catalogue for the Botanic Garden.

"An English list of the trees and plants...with the Latin names added there unto."

Very grand.

It only contains about 1,500 species, but it indicates the growing interest in botany

and it was around this time that some inquisitive minds began to ask, "How do plants grow?"

One of the first to investigate the natural world is an alchemist.

His name is Jan Baptist van Helmont.

'He dabbles in medicine and magic,

'a dangerous combination in the 17th century.

'Science is seen as a threat to God and His creation.

'So when van Helmont suggests that plants could have miraculous healing properties,

'he's asking for trouble. And it's not long before trouble comes knocking at his door.'

In March, 1634, agents of the Spanish Inquisition call at a house in Brussels.

They take 55-year-old Jan Baptist van Helmont away for questioning.

'They interrogate him and put him under house arrest.

'They accuse him of violating God's law.'

His crime? The scientific study of plants and other phenomena.

'Van Helmont is lucky to escape with his life.

'While under house arrest, he starts thinking about a question that's always intrigued him.

'How do plants grow?

'For over 2,000 years, people believed plants grew by eating soil.

'Van Helmont wants to know if this is true,

'so he devises an experiment,

'one that hopefully won't attract the attention of the Spanish Inquisition.'

Van Helmont used a willow tree and a wagon full of soil.

I'm using a bay tree and less soil, but the principle's the same.

The first thing Van Helmont did was to weigh his tree and note its weight.

Next he weighed the soil,

dry soil because he didn't want water to affect its weight.

Van Helmont then planted his tree,

watered it

and his experiment was ready to go.

'Each of my bay trees represents a year in the growth of the willow tree that van Helmont planted.'

He watched it grow for not one year or two years,

but he tended the tree for five years.

And then he re-weighed it.

After five years, the tree has gained a hefty 12 stone.

'The van Helmont dries and weighs the soil.

'The soil weighs almost exactly the same as it did five years ago.'

He concludes the tree has grown not by eating soil, but by drinking water.

After all this effort, van Helmont decides not to publish his results.

He is scared.

And with good reason.

'His experiment relies on evidence, not faith.

'He doesn't want to risk getting on the wrong side of the authorities again,

'so his results are only published after his death.'

For all his personal sacrifice, van Helmont was wrong.

Water IS important for the growth of plants, but it is far from the whole story.

'He misses something fundamental and he isn't the only one.

'I've found a document at my Botanic Garden which shows

'how little people in the 17th century knew about plants.'

Now look at this. This is a plan of the Oxford Botanic Garden in 1675.

And up here in the top right-hand corner is a new addition, a house for plants.

This was the pride and joy of the Director back then.

His baby, his big 17th-century project.

But if you look closely at it, you can see that there's a reason why this wasn't a great success.

There's something missing from this house.

And it's the fact that there are virtually no windows

and those that are there are tiny.

Hardly any windows and no glass in the roof.

They were never going to grow much in here.

What is really interesting about this is that it clearly shows

that 17th-century botanists had not made the connection between the growth of plants and light.

'It sounds obvious to us today, but back then many people believed

'that leaves grew by God's will.

'So suggesting sunlight plays a part is pretty radical.

'It's an important step on the road to understanding photosynthesis.'

In the spring of 1779, a brilliant Dutch physician took a carriage from London

to take the air in the English countryside.

He didn't know it yet, but this pioneering doctor was going to open a new chapter

in the story of how plants grow. His name was Jan Ingenhousz.

As a young man,

he had a gift for science and for medicine, inspired by his father's work as an apothecary,

making remedies for ailments.

His leap to fame came not from studying plants. He was a smallpox inoculator.

'It's a well-paid job,

'so Ingenhousz can afford to rent a plush villa

'He exchanges the distraction of the city for the tranquillity of the countryside

'with a plan to write a book about smallpox,

'but it's the countryside that soon becomes the distraction.'

It wasn't long before Ingenhousz put his book on the back burner.

Instead, he turned his attention to the countryside and the plants that flourished all around him

and he embarked on a series of experiments that would revolutionise our understanding of plants.

'In the late 18th century, it's the fashion among scientists to investigate gases.

'One eminent scientist suggests that plants give off gas.

'Ingenhousz sets up an experiment

'to find out if this is true.'

His test was simple. He collected leaves from his garden and he put them in water.

Ingenhousz then observed his experiment.

When watching plants,

patience is important.

'Ingenhousz believes that if he puts plants under water,

'any gas given off will rise to the surface as bubbles.

'This will give him a clue as to how plants grow.'

As much as he tried, he could not get any of his submerged leaves to give off any gas

until one day his attention is caught by a sample

in a shaft of sunlight.

Once again, Ingenhousz observes his experiment.

After just 10 minutes, something really interesting is happening.

The sample in the shade, same old story, nothing.

But the sample in the shaft of light is different. Tiny bubbles of gas are emerging from the leaves.

For Ingenhousz, this was a really exciting moment.

For the first time, he had made the connection between sunlight and the production of gas in leaves.

'Ingenhousz proves that plants exposed to sunlight do indeed give off a gas.

'Now he wants to find out what that gas is.'

The tiny bubbles of gas released by the leaves have accumulated in the top of the jar.

If I take this glowing splint and put it in there, it re-ignites.

Indicating the presence of oxygen.

'Sunlight triggers the release of oxygen from leaves.

'Ingenhousz knows it's a significant discovery.

'He has to be sure he's right.

'There follows a summer of frenzied activity at the villa.

'The doctor turned botanist repeats the experiment over and over again.'

Ingenhousz used all sorts of leaves from plants in his garden.

Holly, ash, nettles and oak.

Each one he immersed in water and placed one in the sunlight and one in the shade.

He even visited the King's gardener at Kew who gave him leaves of exotic plants like cocoa.

Every leaf that was placed in the sunshine bubbled.

'Ingenhousz wants to know if it's the sun's light or its heat that causes the gas to be released.

'So he puts leaves in water near an open fire and watches them.

'When no bubbles are given off, he knows he's right.

'It's the sun's light, not its heat that's important for the production of gas in plants.

'He then repeats his experiment with different leaves and gets the same result.'

Ingenhousz began to realise that this process was universal.

'His holiday has taken an unexpected turn.

'He arrived a successful doctor,

'he leaves a pioneering botanist, having unlocked a key part of photosynthesis.

'Who would have thought that plants produce a waste product that makes all human and animal life possible?

'Oxygen.'

It would be 100 years before botany took another leap forward

and this advance was made by one of the giants of science,

a man who deserves to be as well-known as Darwin.

'Julius Sachs was born in 1832.

'He has a passion for plants that would come to dominate his life.

'As a schoolboy, Sachs is fascinated by nature.'

He wasn't interested in science, not then. He was just mad about plants.

'Every day before school, he collects and carefully records the local flora.

'As a botanist, I completely understand where he's coming from.

'That desire to surround yourself with plants.

'If you get the bug early, it never leaves you.'

So when Sachs went out into the countryside in Germany to collect flowers,

he was undertaking a very personal activity,

but at the same time joining a tradition that goes back at least four centuries.

You're not just collecting this specimen for yourself,

but for a worldwide record of where particular plants were growing on a particular day.

And around the world there are millions of specimens like this

put together and collected by people like Sachs.

I find it a very satisfying activity.

And...

I'm sure that Sachs found it equally peaceful and rewarding.

'It's a passion that Sachs pursues as he grows up,

'but these idyllic days spent collecting plants are about to come to an abrupt end.'

When Sachs was 17, personal tragedy struck

with the death of his mother, father and one of his brothers in the same year.

He drops out of school.

'Without his parents, the young Sachs is penniless.

'Then a family friend offers him a job at the University of Prague.'

His professor drove him hard.

'He's forced to work long hours in the laboratory.

'The job gives the young Sachs an understanding of the rigorous methodology required of a scientist.

'He has just enough money to live, but not nearly enough time to pursue his real passion -

'plants.

'He turns to drugs to help him stay awake,

'working for his employer during the day and for himself at night.

'Over the next 20 years,

'Sachs conducts thousands of experiments and writes up his results in meticulous detail.'

Sachs toiled for many years before producing this, his Textbook of Experimental Plant Physiology.

It's all in here - the role of light, the need for gases, the need for water.

This book became the standard textbook for plant biologists in Europe.

It was translated into English

and it is a quite, quite beautiful piece of work.

Wonderful, wonderful detail.

It's a true magnum opus.

Phenomenal.

'This book is the making of him.

'Offers of work flood in.

'I've come to Wurzburg in Central Germany.

'It's here that Sachs is appointed head of Europe's top botanical institute in 1868.

'He's just 36 years old.'

So from his undeniably humble origins, Sachs arrives in Wurzburg as the leading botanist in Europe.

He's the head of a big university department with his own research group

and he drives that research group with the same obsession that he drove himself

and he still relies on drugs to keep himself going.

But he was still driven. He still wanted to know more.

He still wanted to know what made plants grow,

how they took that light and what they did with it.

'Only now he has the reputation, money and resources to tackle these big questions.

'This time he's the one driving his colleagues hard.

'Today there's an institute dedicated to Sachs at the University of Wurzburg.

'Professor Markus Riederer is the Director.'

Wow!

These are his paintings he did himself for using them in lectures.

So this is 19th-century Powerpoint!

It is! Only rather more beautiful.

When you step back to where the students saw it, it looks beautifully detailed.

The right scale. Indeed. That's terrific.

So what else have you got? Is this his microscope? It is, yeah.

It says Sachs on it. That's tremendous.

So down here, are these the accounts for the laboratory? No, it's his private accounts.

He had a family - a wife and three children. Did they ever see him?

I cannot believe that. He always worked.

'His personal accounts include a few surprises.'

That's cocaine.

Cocaine. OK. In his accounts. It was legal then.

Oh, OK!

So did that keep him going 14 hours a day? Exactly. To produce this work. Ja, ja.

'Sachs' desire to understand what makes plants grow is all-consuming.

'He knows sunlight produces gas from leaves. This gas is oxygen.

'What he doesn't know is why sunlight is so important.

'Professor Riederer recreates one of Sachs' best-known experiments.'

I have a leaf which has been in the light all day. A normal leaf.

That's a normal leaf that has seen hours of light.

And Sachs wanted to find out what was inside it. Exactly. Enabling it to grow. Exactly.

'By the 19th century, botanists knew that a plant's growth wasn't down to water and sunlight alone.

'Every green plant stores its energy by making something called starch.

'It's a vital component of the human diet and it's the power at the heart of a growing plant.

'Knowing this, he sets out to discover the role sunlight plays in the production of starch.

'He strips the green colour from a leaf and applies iodine to the white leaf.

'He knows that iodine will react with starch produced in the leaf, turning it black.'

The starch is stained now. It certainly is.

Hey, presto!

So this leaf, which had been grown normally in the sunlight, has gone black because it's full of starch.

Yeah.

'Now Sachs tries the experiment again.

'This time he uses a leaf that has seen no sunlight for 12 hours.

'Again, he strips the green colour out of the leaf.

'This time when the iodine is added, nothing happens.

'The leaf stays completely white.

'Having been left in the dark, it contains no starch.

'Sachs carries out one final test.

'Part of a leaf is covered up while another part of the same leaf is left uncovered.'

We have our version of this.

'He then places the leaf in the sunlight.

'If Sachs is right, only those parts of the leaf exposed to the sun should produce starch.'

Part of this leaf should have starch in, the bit that was illuminated.

And the bit in the shade should not.

This is an exciting moment, isn't it? It is exciting. It is.

So on goes the iodine.

We're starting to see some of the tissue... Ah!

Our "Light" is coming out! Now look at that!

It's back to front, but you can already see that the part of the stencil

where the light went through, the leaf is black. So starch has only been formed

on the part of the leaf that was exposed to the light. It's like photography. It is!

That wonderful moment in a darkroom when the picture appears.

So there you are.

Fantastic. And you've got a beautiful demonstration, very elegant, very simple,

that light equals starch, shade equals no starch. That's right.

This was a breakthrough. It was a monumental quantum step up

in our understanding of how plants grow

and it's one of those experiments when you think, "Why didn't I think of that? Why didn't anybody else?"

The fact that Sachs did it

shows just how he was so far above his contemporaries

in plant science, in botany at that time.

'Sachs doesn't stop there.

'He wants to find where in the plant the starch is produced.'

Sometimes science needs new tools to develop and botany was no exception.

When, in the mid-19th century, a new generation of microscopes became available,

Sachs was able to look right inside the leaf.

When he looked down the lens of the microscope,

Sachs could see inside each cell and it must have been as exciting then as it is now.

What he saw inside the cells

were small structures.

Solid structures.

And he realised that this is where the starch was being produced.

And he had found the factory that fuelled the growth of the plant.

And these small structures in each cell are called chloroplasts.

And the energy produced within these chloroplasts

is what goes on to fuel the growth of the plant.

Not only that, but the production of flowers, seeds,

fruit and the next generation.

Now, 150 years later,

we have microscopes that enable us to look inside living cells...

..and reveal what's going on inside them.

Sachs would have been amazed to see

that the chloroplasts are not sitting in the cells

inactive and static, as they were on his microscope slide,

but they are jostling for position,

so that the production of starch is maximised

as the light changes.

It's the most amazingly efficient production system in nature.

As sunlight hits a leaf, the chloroplasts leap into action.

When this short clip is repeated and speeded up,

we can see these chloroplasts vying with each other to grab the sun's rays.

This wonderful dance of the chloroplasts is going on all around us

in what seem like static leaves

and the plant is doing it to ensure that it captures just the right amount of light -

not too little and not too much.

It would have been wonderful to be able to show this to Sachs,

so that he could see that the chloroplasts that he observed...

..are moving in this quite beautiful way.

Plants produce sugars which they store in the form of starch.

Sachs shows where in the plant this happens,

how in fact a plant grows.

Sachs would have been astonished to see what happens inside this potato cell.

To begin with, there's no sign of starch.

Yet just after a few hours sitting in the sunlight, the cell is packed full of starch grains.

In just over 200 years, the pioneers of botany have cracked some of the big questions of photosynthesis.

They knew that plants don't eat soil,

water and sunlight drive growth.

They had also worked out that leaves give off a gas when exposed to the sun.

That gas is oxygen.

And thanks to a devastatingly simple experiment, they knew that plants use sunlight to produce sugars,

a source of energy that gets stored as starch.

All in all, a pretty impressive body of work for the fledgling science of botany.

There is still something missing.

Without it, photosynthesis is impossible.

And it's in the very air we breathe.

Carbon dioxide.

When botanists used microscopes to examine the surface of leaves...

..they discovered something rather surprising.

The underside of a leaf is covered with what looks like tiny pores.

Modern microscopes show these in amazing detail.

They're called stomata and it's through these tiny openings

that plants take in carbon dioxide from the air around them.

These stomata can open and close,

thereby constantly regulating the amount of carbon dioxide getting into the plant.

I'd like to think that a breath I exhaled 30 years ago now exists in the bark of this tree.

There is a direct link

between our lives and the lives of plants.

We give plants carbon dioxide to fuel their growth...

..and they give us the oxygen we need to survive.

Botanists in the 19th century knew that plants absorbed carbon dioxide.

It wasn't until well into the 20th century that they found out what the plant did with it.

It's the last major piece in the photosynthesis puzzle to be solved.

Take a look at this photograph from the 1940s.

It shows two men examining a camera, both of them scientists at the top of their game,

nothing unusual in it at all.

Except behind this photograph is a story of betrayal

and a bitter feud that would last for four decades.

'The man in the white shirt is Andrew Benson.

'Benson is responsible for one of the most important discoveries in the story of photosynthesis.

'His boss is Melvin Calvin,

'a brilliant chemist.

'Both men are working at the University of California at Berkeley.

'Their research is focused on one question -

'what does a plant do with carbon dioxide?

'Professor David Beerling's working life is devoted to the science of plants.

'For him, the meeting of Calvin and Benson is pivotal

'to the understanding of photosynthesis.'

So what do we know about these two men?

Benson was really following his own intuition and experimental programme

and much of the work that he did Calvin was unaware of.

Calvin had a lot going on and he was involved in running this lab and other research questions.

He also had his own personal theory about how photosynthesis was working

and he was very focused on addressing his own particular pet theory,

and all the time you've got Benson looking on and seeing his boss pursuing

what he knew to be, you know, a dead end.

That's not a great basis for a working relationship. Rivals in the same team, no, not at all.

To begin with, things are very different.

Calvin and Benson work closely together,

trying to figure out how plants use carbon dioxide to fuel their growth.

Once again, botany benefits from a leap forward in science.

Foremost among the new technologies of the age is a machine called a cyclotron.

Invented at the Berkeley Radiation Laboratory,

the cyclotron is a particle accelerator.

It allows scientists to study the nucleus of the atom.

CLICKING SOUNDS

But that's not why it interests Benson.

The cyclotron produces radioactive carbon atoms.

'The Atomic Age.

'Here is the answer to a dream as old as Man himself,

'a giant of limitless power at Man's command.

'And where was it science found that giant?

'In the atom.'

If the atom is radioactive, you can follow it wherever it goes.

The idea is to replace the normal carbon atom in carbon dioxide

with a radioactive carbon atom.

By making the carbon dioxide radioactive before a plant takes it in,

Benson believes he can track carbon's journey through the plant.

If this works, Benson will have discovered how a plant uses carbon dioxide,

something no-one else has done before.

For a scientist, it doesn't get any more exciting than this.

At the heart of the experiment is a glass disc shaped like a lollipop.

It contains green algae growing in conditions that are perfect for photosynthesis.

Inside his disc were algae busily photosynthesising away.

When he introduced the radioactive carbon dioxide,

the algae absorbed the gas.

He then killed the algae and the chemical reactions stopped instantly.

'By killing the algae with alcohol, Benson freezes a moment in time.

'He then examines the dead algae to see how they've used the carbon in carbon dioxide to make sugars.

'The radioactive compounds in the algae are separated on to sheets of paper.

'These sheets are then pressed against X-ray sensitive film

'to produce something called a chromatogram.

'Each fuzzy blob here shows where the radioactive carbon has gone.'

Why did a few smudges create so much excitement?

This doesn't look very impressive,

but this must have been their Eureka moment when they started getting these chromatograms. Really? Why?

Because they realised that they could now see some of the key compounds

that had used the radioactive carbon they'd fed the algae. So each blob is a different molecule?

Each of these smudges represents a different chemical compound or a different sugar

that represents a different stage in the pathway to carbon.

'The pathway to carbon is effectively a road map,

'showing how the plant makes sugar.

'Understanding the first step on that road is crucial -

'how a plant splits carbon from carbon dioxide.

'Benson believes the answer lies with a protein that is common to all plants.

'Calvin, on the other hand, has his own grand theory and isn't much interested in what Benson is up to.

'So to begin with, Benson doesn't tell his boss what he's doing.

'Calvin's theory of photosynthesis is eventually proved wrong.

'Benson is the one who gets it right.

'It's Benson who shows what happens during that first crucial step

'when a plant grabs hold of the carbon in carbon dioxide.'

Photosynthesis is often shown as carbon dioxide plus water and light

equals sugar and oxygen.

This seems to imply that that's a gross simplification.

Yes, it's accurate, but it hides a huge amount of detail

and a huge amount of elegance in the biochemistry.

So it's not one big step, it's lots of tiny little hops? That's right.

'Mother Nature doesn't give up her secrets that easily.

'Every smudge has to be identified,

'then they need to figure out how all the compounds work together.

'It's a project that takes ten years to complete.

'Benson receives no recognition for his work.'

It's a familiar story. Someone makes a great discovery...

And someone else takes the credit.

In 1954, Benson is sacked from the university,

leaving Calvin to work on without him.

I want to show you another photo.

It's 1961 and Melvin Calvin is receiving his Nobel Prize

for cracking the role of carbon in photosynthesis,

but there's something or someone missing.

Andrew Benson is nowhere to be seen.

To begin with, both men are credited for their work on photosynthesis.

Now only one name takes centre stage.

The passing of the years did little to soften Calvin's approach to his colleague.

This is Melvin Calvin's autobiography and it tells a story

of how he and his team unlocked the secrets of photosynthesis.

It was published 30 years after he was awarded the Nobel Prize

and in all 175 pages,

there is no mention of Andrew Benson. Not once.

It's as though he never existed.

'Carbon's journey from gas to sugar became known as "the Calvin cycle".

'Today, many botanists recognise Benson's contribution

'and call it "the Calvin-Benson cycle".

'Benson may have missed out on the Nobel Prize, but his contribution hasn't been forgotten.'

So how important is Benson's work?

Andy Benson's discoveries were absolutely amazing.

They filled a huge gap in our knowledge about how plants photosynthesise

and in a sense the discovery of that pathway of how they do that

is comparable to Watson and Crick figuring out the structure of DNA.

Today, we not only know how plants grow,

but with the latest technology, we can watch them grow, cell by cell.

The tip of this root is forcing its way through the earth.

By taking carbon dioxide and converting it into sugars and starch,

the plant has the energy it needs to grow.

It may seem like we now know everything there is to know about photosynthesis...

..but that's not the case.

For instance, the environment in which plants grow can vary dramatically and yet they survive.

Plants are very sophisticated.

From the Equator to the Arctic Circle, they photosynthesise in all sorts of conditions.

And they have to respond to their environment in order to grow.

And even here in Britain, plants have a lot to contend with.

Whether they live high on a hill top

or down on the valley floor,

plants have adapted to where they live.

Take this ivy, for example.

It's growing on a north-facing cliff so it gets no direct sunshine.

Furthermore, it's got trees forming a canopy over the top of it.

It's got no real soil to get its roots into, so it has no permanent supply of water

and yet there's lots of it. It is brilliantly adapted to these growing conditions.

Whether it's poor light or not enough soil,

plants have to make the most of their surroundings.

That's because, unlike me, they're rooted to the spot.

They can't go searching for water if they're thirsty

or find a shady spot to hide from the sun.

Up on the top of the hill, there's plenty of light. That's not a problem.

Here, it's the wind drying out the plants

that makes water the limiting factor for photosynthesis.

Plants either adapt or die,

so they've come up with clever ways to survive.

And we've developed methods to turn this ability to our advantage.

Farmers have learned how to make the most of photosynthesis in all sorts of conditions

and in modern glasshouses, they can manipulate the environment to increase production,

often in ways that are quite surprising.

SHEEP BLEATING

The Netherlands is one of the world's smallest countries,

yet it has become one of the world's biggest food exporters.

In these vast greenhouses,

commercial growers have learned to manipulate the building blocks of photosynthesis.

They don't rely on sunlight to grow crops.

They can make their own with the help of 3,500 light bulbs.

When the sun goes down, the lights come on and the plants continue to grow.

By changing the lighting conditions,

they can bring forward the growing season of these peppers by four weeks.

More light buys the plant more time to turn sugar into fruit.

With sunlight guaranteed, this greenhouse produces 14 million peppers every year.

Sunlight isn't the only part of photosynthesis that can be manipulated to our advantage.

Thanks to a quirk of evolution,

changing the levels of carbon dioxide can also have a dramatic effect.

There have been times in the history of the Earth

when the carbon dioxide levels were very different

and as a result, plants have the capacity to use extra carbon dioxide to make more sugar

and to produce bigger fruit.

Commercial growers have been quick to exploit this legacy of our planet's past.

Today, this Suffolk greenhouse produces 50% of all the tomatoes grown in Britain.

The secret to more tomatoes is more carbon dioxide.

Next door to the greenhouse is this factory.

It generates two waste products.

One is steam which escapes up these chimneys

and the other is carbon dioxide,

a greenhouse gas that you don't want to release into the atmosphere.

So instead, this greenhouse gas gets pumped from the factory into...a greenhouse.

These plastic tubes have tiny holes

which deliver the gas to the leaves of the tomato plants.

Give a tomato plant extra carbon dioxide and it produces more sugar

which makes for a sweeter tomato which is good for us.

It also doubles the yield

which is good for the grower.

By fine-tuning the environment of plants,

we can grow more food.

These commercial growers have got photosynthesis down to a fine art.

They can manipulate it, but that's as far as it goes.

Plants are still doing all the hard work.

Turning water and carbon dioxide into leaves, seeds and fruits makes huge demands on a plant.

To fuel this growth, it needs a reliable source of power.

However different they are, wherever they come from,

plants are all able to survive and grow because of their ability to harness energy from the sun.

The amount of light energy converted by photosynthesis is staggering.

In one year, all the plants on Earth generate enough energy

to power human civilisation six times over.

We now know a great deal about photosynthesis.

We can manipulate it to make better crops and feed more people.

But this is just the start. The next step is really exciting.

And if science gets it right, it will alter lives for generations to come.

At the University of Glasgow, Professor Lee Cronin is trying

to recreate photosynthesis in his laboratory.

Something that plants have been doing for more than a thousand million years,

he is trying to do artificially in a decade.

Plants use the sun's energy to split water into hydrogen and oxygen,

two gases that could help make the fuels of the future.

It's this process that Lee is trying to copy.

This very thin electrode where you see all these very small bubbles

is a platinum electrode where the hydrogen is coming off,

and at this black electrode with the slightly bigger bubble is where the oxygen is being produced.

This normally happens inside a leaf, but here it's happening in this flask. Exactly.

'There's still a long way to go.

'Lee can't split water using just light.

'Not yet anyway.

'He still needs a battery to power the process,

'but the potential is enormous.'

If we let this go long enough, the water in here would get less and less as it's being converted to the gas

and there'd be nothing left at the end. How long would that take?

Probably... Well, at this rate, probably a few days. Right. So we don't need very much water.

There's a huge amount of gas locked up in here.

But this is the critical first step of the photosynthesis story? Yeah, exactly.

Once we've perfected the first step, there is a critical part

where we take carbon dioxide from the atmosphere and complete the story and turn the carbon dioxide

into a fuel that we could put in an aeroplane or a car.

So our family cars could start, in years to come, from a process like this with water being split?

There's every possibility. We're very excited about it. Wow!

'So he should be. The prize is clean and limitless energy.

'No wonder labs like this all over the world are working hard to crack the problem.'

If we get this right, if we're able to understand and learn from photosynthesis in such a way

that we can surpass evolution if you like and make an even better device

to take light energy, carbon dioxide and water and produce a fuel,

then this is going to have massive ramifications for our society and our environment.

Lee's work is impressive,

but it shows how sophisticated photosynthesis is

and scientists will be hard pressed to replicate it.

The thought that it may provide an alternative source of energy

confirms the awesome power of photosynthesis.

To see the power of photosynthesis in action, take a look at these images from NASA.

They show how photosynthesis varies across the globe

with the ebb and flow of the seasons.

That's not the whole story.

What's fascinating is the oceans.

They're glowing green.

That's because half of the world's photosynthesis takes place not on the land, but in the sea.

How close are we to understanding all there is to know about photosynthesis?

We understand the broad principles of how photosynthesis works, but the real fine detail still eludes us.

We can put a man on the moon, but we can't mimic photosynthesis.

Botany has come a long way since the time when people believed plants eat soil.

Today, we can feed more of the world's population.

Tomorrow, we may even find a way to fuel our planet.

And it's all down to photosynthesis,

for me, the most remarkable and important process on Earth.

Next time on Botany: A Blooming History...

I'll be looking at how botanists puzzled over the colours of snapdragons,

investigated the mysteries of wild maize

and developed a brand-new science - plant genetics.

Subtitles by Subtext for Red Bee Media Ltd 2011

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