0:00:09 > 0:00:11'It's nearly summer
0:00:11 > 0:00:15'and the garden is bursting with life.
0:00:15 > 0:00:21'As a botanist, I'm fascinated by what makes plants grow.
0:00:21 > 0:00:25'For instance, to produce all this colour and diversity
0:00:25 > 0:00:29'you need just a few minerals and three basic ingredients.'
0:00:32 > 0:00:35Water, sunlight and carbon dioxide,
0:00:35 > 0:00:39the stuff that I'm breathing out right now.
0:00:39 > 0:00:42And that is all. Nothing else.
0:00:46 > 0:00:54Plants turn these ingredients into food for growth and a waste product we find very useful - oxygen.
0:00:58 > 0:01:00It sounds simple,
0:01:00 > 0:01:05but this process is one of the most fascinating and complicated in the whole of science.
0:01:05 > 0:01:08It's called photosynthesis.
0:01:12 > 0:01:18'It'll take the pioneers of botany over 400 years to work out
0:01:18 > 0:01:20'why a leaf needs sunlight,
0:01:20 > 0:01:24'what role water plays
0:01:24 > 0:01:29'and why a plant can't exist without carbon dioxide.
0:01:31 > 0:01:36'Today photosynthesis is at the forefront of scientific research.'
0:01:36 > 0:01:40If we get this right and learn from photosynthesis,
0:01:40 > 0:01:46- we should be able to produce very quickly a liquid fuel for cars... - No more gasoline, no more diesel?
0:01:46 > 0:01:49No more fossil fuel.
0:01:49 > 0:01:56'Photosynthesis is taking place right now in every leaf of every plant.'
0:01:56 > 0:01:59I find that amazing.
0:02:30 > 0:02:35'The University of Oxford Botanic Garden is the oldest in Britain.
0:02:35 > 0:02:38'I've been Director here for 22 years
0:02:38 > 0:02:42'and one of the great things about the job
0:02:42 > 0:02:44'is that I get to live here.'
0:02:49 > 0:02:55When the gates are locked, this enchanting place becomes my back garden.
0:03:12 > 0:03:17It took botanists a long time to understand the complex process
0:03:17 > 0:03:22that transforms a seed into a fully-grown tree.
0:03:22 > 0:03:28Any scientific journey will have twists and turns. Working out how plants grow was no exception.
0:03:37 > 0:03:42This is the 1648 catalogue for the Botanic Garden.
0:03:42 > 0:03:48"An English list of the trees and plants...with the Latin names added there unto."
0:03:48 > 0:03:50Very grand.
0:03:50 > 0:03:57It only contains about 1,500 species, but it indicates the growing interest in botany
0:03:57 > 0:04:04and it was around this time that some inquisitive minds began to ask, "How do plants grow?"
0:04:08 > 0:04:13One of the first to investigate the natural world is an alchemist.
0:04:14 > 0:04:17His name is Jan Baptist van Helmont.
0:04:20 > 0:04:23'He dabbles in medicine and magic,
0:04:23 > 0:04:27'a dangerous combination in the 17th century.
0:04:28 > 0:04:32'Science is seen as a threat to God and His creation.
0:04:35 > 0:04:41'So when van Helmont suggests that plants could have miraculous healing properties,
0:04:41 > 0:04:47'he's asking for trouble. And it's not long before trouble comes knocking at his door.'
0:04:54 > 0:05:00In March, 1634, agents of the Spanish Inquisition call at a house in Brussels.
0:05:00 > 0:05:04They take 55-year-old Jan Baptist van Helmont away for questioning.
0:05:10 > 0:05:14'They interrogate him and put him under house arrest.
0:05:14 > 0:05:18'They accuse him of violating God's law.'
0:05:18 > 0:05:23His crime? The scientific study of plants and other phenomena.
0:05:25 > 0:05:29'Van Helmont is lucky to escape with his life.
0:05:31 > 0:05:37'While under house arrest, he starts thinking about a question that's always intrigued him.
0:05:38 > 0:05:40'How do plants grow?
0:05:47 > 0:05:52'For over 2,000 years, people believed plants grew by eating soil.
0:05:52 > 0:05:56'Van Helmont wants to know if this is true,
0:05:58 > 0:06:00'so he devises an experiment,
0:06:02 > 0:06:07'one that hopefully won't attract the attention of the Spanish Inquisition.'
0:06:07 > 0:06:12Van Helmont used a willow tree and a wagon full of soil.
0:06:12 > 0:06:16I'm using a bay tree and less soil, but the principle's the same.
0:06:16 > 0:06:22The first thing Van Helmont did was to weigh his tree and note its weight.
0:06:28 > 0:06:30Next he weighed the soil,
0:06:30 > 0:06:35dry soil because he didn't want water to affect its weight.
0:06:40 > 0:06:43Van Helmont then planted his tree,
0:06:46 > 0:06:48watered it
0:06:51 > 0:06:53and his experiment was ready to go.
0:07:00 > 0:07:07'Each of my bay trees represents a year in the growth of the willow tree that van Helmont planted.'
0:07:09 > 0:07:13He watched it grow for not one year or two years,
0:07:13 > 0:07:16but he tended the tree for five years.
0:07:16 > 0:07:18And then he re-weighed it.
0:07:22 > 0:07:26After five years, the tree has gained a hefty 12 stone.
0:07:30 > 0:07:34'The van Helmont dries and weighs the soil.
0:07:34 > 0:07:38'The soil weighs almost exactly the same as it did five years ago.'
0:07:41 > 0:07:47He concludes the tree has grown not by eating soil, but by drinking water.
0:07:58 > 0:08:02After all this effort, van Helmont decides not to publish his results.
0:08:02 > 0:08:05He is scared.
0:08:06 > 0:08:08And with good reason.
0:08:08 > 0:08:12'His experiment relies on evidence, not faith.
0:08:12 > 0:08:19'He doesn't want to risk getting on the wrong side of the authorities again,
0:08:19 > 0:08:23'so his results are only published after his death.'
0:08:25 > 0:08:29For all his personal sacrifice, van Helmont was wrong.
0:08:29 > 0:08:35Water IS important for the growth of plants, but it is far from the whole story.
0:08:38 > 0:08:43'He misses something fundamental and he isn't the only one.
0:08:47 > 0:08:51'I've found a document at my Botanic Garden which shows
0:08:51 > 0:08:56'how little people in the 17th century knew about plants.'
0:08:58 > 0:09:04Now look at this. This is a plan of the Oxford Botanic Garden in 1675.
0:09:04 > 0:09:10And up here in the top right-hand corner is a new addition, a house for plants.
0:09:10 > 0:09:14This was the pride and joy of the Director back then.
0:09:14 > 0:09:18His baby, his big 17th-century project.
0:09:20 > 0:09:27But if you look closely at it, you can see that there's a reason why this wasn't a great success.
0:09:28 > 0:09:31There's something missing from this house.
0:09:31 > 0:09:36And it's the fact that there are virtually no windows
0:09:36 > 0:09:39and those that are there are tiny.
0:09:39 > 0:09:43Hardly any windows and no glass in the roof.
0:09:43 > 0:09:47They were never going to grow much in here.
0:09:47 > 0:09:51What is really interesting about this is that it clearly shows
0:09:51 > 0:09:58that 17th-century botanists had not made the connection between the growth of plants and light.
0:10:00 > 0:10:05'It sounds obvious to us today, but back then many people believed
0:10:05 > 0:10:08'that leaves grew by God's will.
0:10:09 > 0:10:13'So suggesting sunlight plays a part is pretty radical.
0:10:14 > 0:10:19'It's an important step on the road to understanding photosynthesis.'
0:10:37 > 0:10:43In the spring of 1779, a brilliant Dutch physician took a carriage from London
0:10:43 > 0:10:47to take the air in the English countryside.
0:10:47 > 0:10:53He didn't know it yet, but this pioneering doctor was going to open a new chapter
0:10:53 > 0:10:58in the story of how plants grow. His name was Jan Ingenhousz.
0:11:09 > 0:11:11As a young man,
0:11:11 > 0:11:17he had a gift for science and for medicine, inspired by his father's work as an apothecary,
0:11:17 > 0:11:19making remedies for ailments.
0:11:19 > 0:11:25His leap to fame came not from studying plants. He was a smallpox inoculator.
0:11:30 > 0:11:32'It's a well-paid job,
0:11:32 > 0:11:36'so Ingenhousz can afford to rent a plush villa
0:11:36 > 0:11:42'He exchanges the distraction of the city for the tranquillity of the countryside
0:11:42 > 0:11:46'with a plan to write a book about smallpox,
0:11:46 > 0:11:51'but it's the countryside that soon becomes the distraction.'
0:11:55 > 0:11:59It wasn't long before Ingenhousz put his book on the back burner.
0:11:59 > 0:12:05Instead, he turned his attention to the countryside and the plants that flourished all around him
0:12:05 > 0:12:12and he embarked on a series of experiments that would revolutionise our understanding of plants.
0:12:12 > 0:12:18'In the late 18th century, it's the fashion among scientists to investigate gases.
0:12:18 > 0:12:23'One eminent scientist suggests that plants give off gas.
0:12:24 > 0:12:27'Ingenhousz sets up an experiment
0:12:27 > 0:12:30'to find out if this is true.'
0:12:30 > 0:12:36His test was simple. He collected leaves from his garden and he put them in water.
0:12:36 > 0:12:40Ingenhousz then observed his experiment.
0:12:40 > 0:12:42When watching plants,
0:12:42 > 0:12:45patience is important.
0:12:53 > 0:12:57'Ingenhousz believes that if he puts plants under water,
0:12:57 > 0:13:02'any gas given off will rise to the surface as bubbles.
0:13:03 > 0:13:07'This will give him a clue as to how plants grow.'
0:13:12 > 0:13:18As much as he tried, he could not get any of his submerged leaves to give off any gas
0:13:18 > 0:13:22until one day his attention is caught by a sample
0:13:22 > 0:13:25in a shaft of sunlight.
0:13:25 > 0:13:29Once again, Ingenhousz observes his experiment.
0:13:38 > 0:13:42After just 10 minutes, something really interesting is happening.
0:13:42 > 0:13:47The sample in the shade, same old story, nothing.
0:13:47 > 0:13:53But the sample in the shaft of light is different. Tiny bubbles of gas are emerging from the leaves.
0:13:53 > 0:13:56For Ingenhousz, this was a really exciting moment.
0:13:57 > 0:14:04For the first time, he had made the connection between sunlight and the production of gas in leaves.
0:14:06 > 0:14:12'Ingenhousz proves that plants exposed to sunlight do indeed give off a gas.
0:14:12 > 0:14:16'Now he wants to find out what that gas is.'
0:14:24 > 0:14:30The tiny bubbles of gas released by the leaves have accumulated in the top of the jar.
0:14:30 > 0:14:35If I take this glowing splint and put it in there, it re-ignites.
0:14:36 > 0:14:39Indicating the presence of oxygen.
0:14:45 > 0:14:49'Sunlight triggers the release of oxygen from leaves.
0:14:49 > 0:14:53'Ingenhousz knows it's a significant discovery.
0:14:53 > 0:14:56'He has to be sure he's right.
0:14:58 > 0:15:02'There follows a summer of frenzied activity at the villa.
0:15:05 > 0:15:09'The doctor turned botanist repeats the experiment over and over again.'
0:15:13 > 0:15:18Ingenhousz used all sorts of leaves from plants in his garden.
0:15:18 > 0:15:22Holly, ash, nettles and oak.
0:15:22 > 0:15:28Each one he immersed in water and placed one in the sunlight and one in the shade.
0:15:30 > 0:15:36He even visited the King's gardener at Kew who gave him leaves of exotic plants like cocoa.
0:15:36 > 0:15:40Every leaf that was placed in the sunshine bubbled.
0:15:44 > 0:15:50'Ingenhousz wants to know if it's the sun's light or its heat that causes the gas to be released.
0:15:50 > 0:15:55'So he puts leaves in water near an open fire and watches them.
0:15:55 > 0:15:59'When no bubbles are given off, he knows he's right.
0:15:59 > 0:16:06'It's the sun's light, not its heat that's important for the production of gas in plants.
0:16:07 > 0:16:13'He then repeats his experiment with different leaves and gets the same result.'
0:16:14 > 0:16:19Ingenhousz began to realise that this process was universal.
0:16:20 > 0:16:24'His holiday has taken an unexpected turn.
0:16:24 > 0:16:27'He arrived a successful doctor,
0:16:27 > 0:16:34'he leaves a pioneering botanist, having unlocked a key part of photosynthesis.
0:16:40 > 0:16:47'Who would have thought that plants produce a waste product that makes all human and animal life possible?
0:16:47 > 0:16:49'Oxygen.'
0:17:01 > 0:17:06It would be 100 years before botany took another leap forward
0:17:06 > 0:17:12and this advance was made by one of the giants of science,
0:17:12 > 0:17:17a man who deserves to be as well-known as Darwin.
0:17:22 > 0:17:25'Julius Sachs was born in 1832.
0:17:25 > 0:17:31'He has a passion for plants that would come to dominate his life.
0:17:35 > 0:17:40'As a schoolboy, Sachs is fascinated by nature.'
0:17:41 > 0:17:46He wasn't interested in science, not then. He was just mad about plants.
0:17:49 > 0:17:55'Every day before school, he collects and carefully records the local flora.
0:17:56 > 0:18:00'As a botanist, I completely understand where he's coming from.
0:18:00 > 0:18:04'That desire to surround yourself with plants.
0:18:04 > 0:18:08'If you get the bug early, it never leaves you.'
0:18:10 > 0:18:15So when Sachs went out into the countryside in Germany to collect flowers,
0:18:15 > 0:18:19he was undertaking a very personal activity,
0:18:20 > 0:18:26but at the same time joining a tradition that goes back at least four centuries.
0:18:26 > 0:18:31You're not just collecting this specimen for yourself,
0:18:31 > 0:18:37but for a worldwide record of where particular plants were growing on a particular day.
0:18:37 > 0:18:43And around the world there are millions of specimens like this
0:18:43 > 0:18:47put together and collected by people like Sachs.
0:18:47 > 0:18:51I find it a very satisfying activity.
0:18:51 > 0:18:53And...
0:18:53 > 0:18:58I'm sure that Sachs found it equally peaceful and rewarding.
0:18:59 > 0:19:03'It's a passion that Sachs pursues as he grows up,
0:19:03 > 0:19:09'but these idyllic days spent collecting plants are about to come to an abrupt end.'
0:19:13 > 0:19:17When Sachs was 17, personal tragedy struck
0:19:17 > 0:19:23with the death of his mother, father and one of his brothers in the same year.
0:19:25 > 0:19:28He drops out of school.
0:19:28 > 0:19:32'Without his parents, the young Sachs is penniless.
0:19:32 > 0:19:37'Then a family friend offers him a job at the University of Prague.'
0:19:38 > 0:19:40His professor drove him hard.
0:19:42 > 0:19:46'He's forced to work long hours in the laboratory.
0:19:47 > 0:19:54'The job gives the young Sachs an understanding of the rigorous methodology required of a scientist.
0:19:57 > 0:20:04'He has just enough money to live, but not nearly enough time to pursue his real passion -
0:20:04 > 0:20:05'plants.
0:20:07 > 0:20:11'He turns to drugs to help him stay awake,
0:20:12 > 0:20:17'working for his employer during the day and for himself at night.
0:20:19 > 0:20:22'Over the next 20 years,
0:20:22 > 0:20:28'Sachs conducts thousands of experiments and writes up his results in meticulous detail.'
0:20:29 > 0:20:37Sachs toiled for many years before producing this, his Textbook of Experimental Plant Physiology.
0:20:39 > 0:20:46It's all in here - the role of light, the need for gases, the need for water.
0:20:49 > 0:20:55This book became the standard textbook for plant biologists in Europe.
0:20:55 > 0:20:58It was translated into English
0:20:58 > 0:21:02and it is a quite, quite beautiful piece of work.
0:21:04 > 0:21:06Wonderful, wonderful detail.
0:21:06 > 0:21:09It's a true magnum opus.
0:21:10 > 0:21:12Phenomenal.
0:21:17 > 0:21:20'This book is the making of him.
0:21:20 > 0:21:22'Offers of work flood in.
0:21:30 > 0:21:35'I've come to Wurzburg in Central Germany.
0:21:36 > 0:21:42'It's here that Sachs is appointed head of Europe's top botanical institute in 1868.
0:21:44 > 0:21:47'He's just 36 years old.'
0:21:49 > 0:21:56So from his undeniably humble origins, Sachs arrives in Wurzburg as the leading botanist in Europe.
0:21:56 > 0:22:01He's the head of a big university department with his own research group
0:22:01 > 0:22:07and he drives that research group with the same obsession that he drove himself
0:22:07 > 0:22:13and he still relies on drugs to keep himself going.
0:22:17 > 0:22:22But he was still driven. He still wanted to know more.
0:22:22 > 0:22:26He still wanted to know what made plants grow,
0:22:26 > 0:22:30how they took that light and what they did with it.
0:22:32 > 0:22:38'Only now he has the reputation, money and resources to tackle these big questions.
0:22:40 > 0:22:44'This time he's the one driving his colleagues hard.
0:22:50 > 0:22:56'Today there's an institute dedicated to Sachs at the University of Wurzburg.
0:22:56 > 0:23:00'Professor Markus Riederer is the Director.'
0:23:00 > 0:23:01Wow!
0:23:02 > 0:23:08These are his paintings he did himself for using them in lectures.
0:23:08 > 0:23:10So this is 19th-century Powerpoint!
0:23:10 > 0:23:13- It is!- Only rather more beautiful.
0:23:13 > 0:23:19When you step back to where the students saw it, it looks beautifully detailed.
0:23:19 > 0:23:23- The right scale.- Indeed. That's terrific.
0:23:23 > 0:23:28- So what else have you got? Is this his microscope?- It is, yeah.
0:23:28 > 0:23:32- It says Sachs on it. - That's tremendous.
0:23:32 > 0:23:38- So down here, are these the accounts for the laboratory? - No, it's his private accounts.
0:23:38 > 0:23:42- He had a family - a wife and three children.- Did they ever see him?
0:23:42 > 0:23:46I cannot believe that. He always worked.
0:23:46 > 0:23:51'His personal accounts include a few surprises.'
0:23:52 > 0:23:54That's cocaine.
0:23:54 > 0:23:58- Cocaine. OK. In his accounts. - It was legal then.
0:23:58 > 0:24:00Oh, OK!
0:24:00 > 0:24:06- So did that keep him going 14 hours a day?- Exactly. - To produce this work.- Ja, ja.
0:24:08 > 0:24:14'Sachs' desire to understand what makes plants grow is all-consuming.
0:24:14 > 0:24:18'He knows sunlight produces gas from leaves. This gas is oxygen.
0:24:18 > 0:24:23'What he doesn't know is why sunlight is so important.
0:24:25 > 0:24:29'Professor Riederer recreates one of Sachs' best-known experiments.'
0:24:29 > 0:24:34- I have a leaf which has been in the light all day.- A normal leaf.
0:24:34 > 0:24:38That's a normal leaf that has seen hours of light.
0:24:38 > 0:24:45- And Sachs wanted to find out what was inside it.- Exactly. - Enabling it to grow.- Exactly.
0:24:49 > 0:24:56'By the 19th century, botanists knew that a plant's growth wasn't down to water and sunlight alone.
0:24:56 > 0:25:01'Every green plant stores its energy by making something called starch.
0:25:01 > 0:25:09'It's a vital component of the human diet and it's the power at the heart of a growing plant.
0:25:10 > 0:25:16'Knowing this, he sets out to discover the role sunlight plays in the production of starch.
0:25:16 > 0:25:22'He strips the green colour from a leaf and applies iodine to the white leaf.
0:25:24 > 0:25:29'He knows that iodine will react with starch produced in the leaf, turning it black.'
0:25:32 > 0:25:36- The starch is stained now. - It certainly is.
0:25:36 > 0:25:38Hey, presto!
0:25:38 > 0:25:44So this leaf, which had been grown normally in the sunlight, has gone black because it's full of starch.
0:25:44 > 0:25:46Yeah.
0:25:46 > 0:25:49'Now Sachs tries the experiment again.
0:25:49 > 0:25:55'This time he uses a leaf that has seen no sunlight for 12 hours.
0:25:55 > 0:25:59'Again, he strips the green colour out of the leaf.
0:26:03 > 0:26:06'This time when the iodine is added, nothing happens.
0:26:06 > 0:26:09'The leaf stays completely white.
0:26:09 > 0:26:14'Having been left in the dark, it contains no starch.
0:26:16 > 0:26:19'Sachs carries out one final test.
0:26:19 > 0:26:25'Part of a leaf is covered up while another part of the same leaf is left uncovered.'
0:26:27 > 0:26:30We have our version of this.
0:26:33 > 0:26:36'He then places the leaf in the sunlight.
0:26:40 > 0:26:46'If Sachs is right, only those parts of the leaf exposed to the sun should produce starch.'
0:26:49 > 0:26:54Part of this leaf should have starch in, the bit that was illuminated.
0:26:54 > 0:26:56And the bit in the shade should not.
0:26:56 > 0:27:01- This is an exciting moment, isn't it?- It is exciting.- It is.
0:27:02 > 0:27:04So on goes the iodine.
0:27:07 > 0:27:13We're starting to see some of the tissue... Ah!
0:27:13 > 0:27:17- Our "Light" is coming out! - Now look at that!
0:27:17 > 0:27:24It's back to front, but you can already see that the part of the stencil
0:27:24 > 0:27:29where the light went through, the leaf is black. So starch has only been formed
0:27:29 > 0:27:35- on the part of the leaf that was exposed to the light. - It's like photography.- It is!
0:27:35 > 0:27:40That wonderful moment in a darkroom when the picture appears.
0:27:40 > 0:27:42So there you are.
0:27:42 > 0:27:49Fantastic. And you've got a beautiful demonstration, very elegant, very simple,
0:27:49 > 0:27:55- that light equals starch, shade equals no starch. - That's right.
0:28:03 > 0:28:08This was a breakthrough. It was a monumental quantum step up
0:28:08 > 0:28:11in our understanding of how plants grow
0:28:11 > 0:28:18and it's one of those experiments when you think, "Why didn't I think of that? Why didn't anybody else?"
0:28:18 > 0:28:21The fact that Sachs did it
0:28:23 > 0:28:28shows just how he was so far above his contemporaries
0:28:28 > 0:28:32in plant science, in botany at that time.
0:28:39 > 0:28:41'Sachs doesn't stop there.
0:28:41 > 0:28:45'He wants to find where in the plant the starch is produced.'
0:28:51 > 0:28:57Sometimes science needs new tools to develop and botany was no exception.
0:28:57 > 0:29:03When, in the mid-19th century, a new generation of microscopes became available,
0:29:03 > 0:29:07Sachs was able to look right inside the leaf.
0:29:08 > 0:29:12When he looked down the lens of the microscope,
0:29:12 > 0:29:18Sachs could see inside each cell and it must have been as exciting then as it is now.
0:29:18 > 0:29:21What he saw inside the cells
0:29:21 > 0:29:24were small structures.
0:29:25 > 0:29:28Solid structures.
0:29:28 > 0:29:32And he realised that this is where the starch was being produced.
0:29:32 > 0:29:37And he had found the factory that fuelled the growth of the plant.
0:29:37 > 0:29:42And these small structures in each cell are called chloroplasts.
0:29:44 > 0:29:49And the energy produced within these chloroplasts
0:29:49 > 0:29:53is what goes on to fuel the growth of the plant.
0:29:53 > 0:29:57Not only that, but the production of flowers, seeds,
0:29:57 > 0:30:00fruit and the next generation.
0:30:02 > 0:30:05Now, 150 years later,
0:30:05 > 0:30:11we have microscopes that enable us to look inside living cells...
0:30:12 > 0:30:16..and reveal what's going on inside them.
0:30:17 > 0:30:19Sachs would have been amazed to see
0:30:19 > 0:30:24that the chloroplasts are not sitting in the cells
0:30:24 > 0:30:28inactive and static, as they were on his microscope slide,
0:30:28 > 0:30:32but they are jostling for position,
0:30:32 > 0:30:35so that the production of starch is maximised
0:30:35 > 0:30:37as the light changes.
0:30:37 > 0:30:42It's the most amazingly efficient production system in nature.
0:30:43 > 0:30:47As sunlight hits a leaf, the chloroplasts leap into action.
0:30:48 > 0:30:52When this short clip is repeated and speeded up,
0:30:52 > 0:30:58we can see these chloroplasts vying with each other to grab the sun's rays.
0:30:59 > 0:31:06This wonderful dance of the chloroplasts is going on all around us
0:31:06 > 0:31:09in what seem like static leaves
0:31:09 > 0:31:16and the plant is doing it to ensure that it captures just the right amount of light -
0:31:16 > 0:31:18not too little and not too much.
0:31:20 > 0:31:25It would have been wonderful to be able to show this to Sachs,
0:31:25 > 0:31:30so that he could see that the chloroplasts that he observed...
0:31:31 > 0:31:36..are moving in this quite beautiful way.
0:31:38 > 0:31:42Plants produce sugars which they store in the form of starch.
0:31:42 > 0:31:46Sachs shows where in the plant this happens,
0:31:46 > 0:31:49how in fact a plant grows.
0:31:51 > 0:31:56Sachs would have been astonished to see what happens inside this potato cell.
0:31:57 > 0:32:01To begin with, there's no sign of starch.
0:32:03 > 0:32:09Yet just after a few hours sitting in the sunlight, the cell is packed full of starch grains.
0:32:14 > 0:32:22In just over 200 years, the pioneers of botany have cracked some of the big questions of photosynthesis.
0:32:25 > 0:32:28They knew that plants don't eat soil,
0:32:28 > 0:32:30water and sunlight drive growth.
0:32:30 > 0:32:36They had also worked out that leaves give off a gas when exposed to the sun.
0:32:36 > 0:32:39That gas is oxygen.
0:32:41 > 0:32:47And thanks to a devastatingly simple experiment, they knew that plants use sunlight to produce sugars,
0:32:47 > 0:32:51a source of energy that gets stored as starch.
0:32:53 > 0:32:59All in all, a pretty impressive body of work for the fledgling science of botany.
0:32:59 > 0:33:02There is still something missing.
0:33:02 > 0:33:05Without it, photosynthesis is impossible.
0:33:05 > 0:33:08And it's in the very air we breathe.
0:33:09 > 0:33:11Carbon dioxide.
0:33:11 > 0:33:16When botanists used microscopes to examine the surface of leaves...
0:33:17 > 0:33:21..they discovered something rather surprising.
0:33:25 > 0:33:31The underside of a leaf is covered with what looks like tiny pores.
0:33:31 > 0:33:35Modern microscopes show these in amazing detail.
0:33:37 > 0:33:41They're called stomata and it's through these tiny openings
0:33:41 > 0:33:45that plants take in carbon dioxide from the air around them.
0:33:48 > 0:33:50These stomata can open and close,
0:33:50 > 0:33:56thereby constantly regulating the amount of carbon dioxide getting into the plant.
0:34:02 > 0:34:08I'd like to think that a breath I exhaled 30 years ago now exists in the bark of this tree.
0:34:10 > 0:34:12There is a direct link
0:34:12 > 0:34:16between our lives and the lives of plants.
0:34:18 > 0:34:22We give plants carbon dioxide to fuel their growth...
0:34:23 > 0:34:27..and they give us the oxygen we need to survive.
0:34:29 > 0:34:34Botanists in the 19th century knew that plants absorbed carbon dioxide.
0:34:34 > 0:34:41It wasn't until well into the 20th century that they found out what the plant did with it.
0:34:41 > 0:34:46It's the last major piece in the photosynthesis puzzle to be solved.
0:35:08 > 0:35:12Take a look at this photograph from the 1940s.
0:35:12 > 0:35:18It shows two men examining a camera, both of them scientists at the top of their game,
0:35:18 > 0:35:21nothing unusual in it at all.
0:35:21 > 0:35:25Except behind this photograph is a story of betrayal
0:35:25 > 0:35:30and a bitter feud that would last for four decades.
0:35:32 > 0:35:35'The man in the white shirt is Andrew Benson.
0:35:37 > 0:35:43'Benson is responsible for one of the most important discoveries in the story of photosynthesis.
0:35:43 > 0:35:46'His boss is Melvin Calvin,
0:35:46 > 0:35:49'a brilliant chemist.
0:35:50 > 0:35:55'Both men are working at the University of California at Berkeley.
0:35:56 > 0:36:00'Their research is focused on one question -
0:36:00 > 0:36:04'what does a plant do with carbon dioxide?
0:36:09 > 0:36:14'Professor David Beerling's working life is devoted to the science of plants.
0:36:17 > 0:36:21'For him, the meeting of Calvin and Benson is pivotal
0:36:21 > 0:36:24'to the understanding of photosynthesis.'
0:36:25 > 0:36:29So what do we know about these two men?
0:36:29 > 0:36:33Benson was really following his own intuition and experimental programme
0:36:33 > 0:36:38and much of the work that he did Calvin was unaware of.
0:36:38 > 0:36:43Calvin had a lot going on and he was involved in running this lab and other research questions.
0:36:43 > 0:36:48He also had his own personal theory about how photosynthesis was working
0:36:48 > 0:36:53and he was very focused on addressing his own particular pet theory,
0:36:53 > 0:36:58and all the time you've got Benson looking on and seeing his boss pursuing
0:36:58 > 0:37:01what he knew to be, you know, a dead end.
0:37:01 > 0:37:07- That's not a great basis for a working relationship.- Rivals in the same team, no, not at all.
0:37:10 > 0:37:13To begin with, things are very different.
0:37:13 > 0:37:16Calvin and Benson work closely together,
0:37:16 > 0:37:21trying to figure out how plants use carbon dioxide to fuel their growth.
0:37:24 > 0:37:29Once again, botany benefits from a leap forward in science.
0:37:31 > 0:37:37Foremost among the new technologies of the age is a machine called a cyclotron.
0:37:37 > 0:37:40Invented at the Berkeley Radiation Laboratory,
0:37:40 > 0:37:43the cyclotron is a particle accelerator.
0:37:43 > 0:37:47It allows scientists to study the nucleus of the atom.
0:37:47 > 0:37:49CLICKING SOUNDS
0:37:49 > 0:37:53But that's not why it interests Benson.
0:37:53 > 0:37:57The cyclotron produces radioactive carbon atoms.
0:37:59 > 0:38:01'The Atomic Age.
0:38:01 > 0:38:06'Here is the answer to a dream as old as Man himself,
0:38:06 > 0:38:10'a giant of limitless power at Man's command.
0:38:10 > 0:38:13'And where was it science found that giant?
0:38:13 > 0:38:15'In the atom.'
0:38:17 > 0:38:22If the atom is radioactive, you can follow it wherever it goes.
0:38:26 > 0:38:31The idea is to replace the normal carbon atom in carbon dioxide
0:38:31 > 0:38:34with a radioactive carbon atom.
0:38:35 > 0:38:40By making the carbon dioxide radioactive before a plant takes it in,
0:38:40 > 0:38:45Benson believes he can track carbon's journey through the plant.
0:38:47 > 0:38:53If this works, Benson will have discovered how a plant uses carbon dioxide,
0:38:53 > 0:38:56something no-one else has done before.
0:38:56 > 0:39:00For a scientist, it doesn't get any more exciting than this.
0:39:15 > 0:39:20At the heart of the experiment is a glass disc shaped like a lollipop.
0:39:20 > 0:39:26It contains green algae growing in conditions that are perfect for photosynthesis.
0:39:29 > 0:39:34Inside his disc were algae busily photosynthesising away.
0:39:34 > 0:39:37When he introduced the radioactive carbon dioxide,
0:39:37 > 0:39:40the algae absorbed the gas.
0:39:40 > 0:39:46He then killed the algae and the chemical reactions stopped instantly.
0:39:47 > 0:39:52'By killing the algae with alcohol, Benson freezes a moment in time.
0:39:52 > 0:39:59'He then examines the dead algae to see how they've used the carbon in carbon dioxide to make sugars.
0:40:03 > 0:40:09'The radioactive compounds in the algae are separated on to sheets of paper.
0:40:10 > 0:40:14'These sheets are then pressed against X-ray sensitive film
0:40:14 > 0:40:17'to produce something called a chromatogram.
0:40:19 > 0:40:24'Each fuzzy blob here shows where the radioactive carbon has gone.'
0:40:26 > 0:40:29Why did a few smudges create so much excitement?
0:40:29 > 0:40:32This doesn't look very impressive,
0:40:32 > 0:40:38- but this must have been their Eureka moment when they started getting these chromatograms.- Really? Why?
0:40:38 > 0:40:43Because they realised that they could now see some of the key compounds
0:40:43 > 0:40:49- that had used the radioactive carbon they'd fed the algae.- So each blob is a different molecule?
0:40:49 > 0:40:55Each of these smudges represents a different chemical compound or a different sugar
0:40:55 > 0:40:58that represents a different stage in the pathway to carbon.
0:41:02 > 0:41:06'The pathway to carbon is effectively a road map,
0:41:06 > 0:41:09'showing how the plant makes sugar.
0:41:10 > 0:41:14'Understanding the first step on that road is crucial -
0:41:14 > 0:41:18'how a plant splits carbon from carbon dioxide.
0:41:18 > 0:41:24'Benson believes the answer lies with a protein that is common to all plants.
0:41:25 > 0:41:32'Calvin, on the other hand, has his own grand theory and isn't much interested in what Benson is up to.
0:41:35 > 0:41:39'So to begin with, Benson doesn't tell his boss what he's doing.
0:41:42 > 0:41:47'Calvin's theory of photosynthesis is eventually proved wrong.
0:41:49 > 0:41:52'Benson is the one who gets it right.
0:41:52 > 0:41:56'It's Benson who shows what happens during that first crucial step
0:41:56 > 0:42:00'when a plant grabs hold of the carbon in carbon dioxide.'
0:42:02 > 0:42:07Photosynthesis is often shown as carbon dioxide plus water and light
0:42:07 > 0:42:10equals sugar and oxygen.
0:42:10 > 0:42:13This seems to imply that that's a gross simplification.
0:42:13 > 0:42:17Yes, it's accurate, but it hides a huge amount of detail
0:42:17 > 0:42:21and a huge amount of elegance in the biochemistry.
0:42:21 > 0:42:25- So it's not one big step, it's lots of tiny little hops?- That's right.
0:42:25 > 0:42:30'Mother Nature doesn't give up her secrets that easily.
0:42:31 > 0:42:34'Every smudge has to be identified,
0:42:34 > 0:42:39'then they need to figure out how all the compounds work together.
0:42:39 > 0:42:43'It's a project that takes ten years to complete.
0:42:47 > 0:42:51'Benson receives no recognition for his work.'
0:42:56 > 0:43:00It's a familiar story. Someone makes a great discovery...
0:43:01 > 0:43:03And someone else takes the credit.
0:43:06 > 0:43:10In 1954, Benson is sacked from the university,
0:43:10 > 0:43:14leaving Calvin to work on without him.
0:43:19 > 0:43:22I want to show you another photo.
0:43:22 > 0:43:26It's 1961 and Melvin Calvin is receiving his Nobel Prize
0:43:26 > 0:43:30for cracking the role of carbon in photosynthesis,
0:43:30 > 0:43:33but there's something or someone missing.
0:43:36 > 0:43:39Andrew Benson is nowhere to be seen.
0:43:43 > 0:43:47To begin with, both men are credited for their work on photosynthesis.
0:43:51 > 0:43:54Now only one name takes centre stage.
0:44:00 > 0:44:06The passing of the years did little to soften Calvin's approach to his colleague.
0:44:08 > 0:44:12This is Melvin Calvin's autobiography and it tells a story
0:44:12 > 0:44:17of how he and his team unlocked the secrets of photosynthesis.
0:44:17 > 0:44:21It was published 30 years after he was awarded the Nobel Prize
0:44:21 > 0:44:25and in all 175 pages,
0:44:25 > 0:44:28there is no mention of Andrew Benson. Not once.
0:44:28 > 0:44:31It's as though he never existed.
0:44:37 > 0:44:42'Carbon's journey from gas to sugar became known as "the Calvin cycle".
0:44:44 > 0:44:49'Today, many botanists recognise Benson's contribution
0:44:49 > 0:44:52'and call it "the Calvin-Benson cycle".
0:44:58 > 0:45:04'Benson may have missed out on the Nobel Prize, but his contribution hasn't been forgotten.'
0:45:04 > 0:45:07So how important is Benson's work?
0:45:07 > 0:45:12Andy Benson's discoveries were absolutely amazing.
0:45:12 > 0:45:17They filled a huge gap in our knowledge about how plants photosynthesise
0:45:17 > 0:45:21and in a sense the discovery of that pathway of how they do that
0:45:21 > 0:45:25is comparable to Watson and Crick figuring out the structure of DNA.
0:45:29 > 0:45:32Today, we not only know how plants grow,
0:45:32 > 0:45:38but with the latest technology, we can watch them grow, cell by cell.
0:45:40 > 0:45:45The tip of this root is forcing its way through the earth.
0:45:45 > 0:45:49By taking carbon dioxide and converting it into sugars and starch,
0:45:49 > 0:45:53the plant has the energy it needs to grow.
0:46:05 > 0:46:11It may seem like we now know everything there is to know about photosynthesis...
0:46:12 > 0:46:14..but that's not the case.
0:46:15 > 0:46:21For instance, the environment in which plants grow can vary dramatically and yet they survive.
0:46:25 > 0:46:28Plants are very sophisticated.
0:46:28 > 0:46:34From the Equator to the Arctic Circle, they photosynthesise in all sorts of conditions.
0:46:34 > 0:46:39And they have to respond to their environment in order to grow.
0:46:39 > 0:46:43And even here in Britain, plants have a lot to contend with.
0:46:49 > 0:46:52Whether they live high on a hill top
0:46:52 > 0:46:54or down on the valley floor,
0:46:54 > 0:46:58plants have adapted to where they live.
0:46:58 > 0:47:00Take this ivy, for example.
0:47:00 > 0:47:04It's growing on a north-facing cliff so it gets no direct sunshine.
0:47:04 > 0:47:09Furthermore, it's got trees forming a canopy over the top of it.
0:47:09 > 0:47:15It's got no real soil to get its roots into, so it has no permanent supply of water
0:47:15 > 0:47:20and yet there's lots of it. It is brilliantly adapted to these growing conditions.
0:47:27 > 0:47:31Whether it's poor light or not enough soil,
0:47:31 > 0:47:35plants have to make the most of their surroundings.
0:47:35 > 0:47:38That's because, unlike me, they're rooted to the spot.
0:47:39 > 0:47:43They can't go searching for water if they're thirsty
0:47:43 > 0:47:46or find a shady spot to hide from the sun.
0:47:47 > 0:47:52Up on the top of the hill, there's plenty of light. That's not a problem.
0:47:52 > 0:47:55Here, it's the wind drying out the plants
0:47:55 > 0:47:59that makes water the limiting factor for photosynthesis.
0:48:05 > 0:48:08Plants either adapt or die,
0:48:08 > 0:48:12so they've come up with clever ways to survive.
0:48:13 > 0:48:18And we've developed methods to turn this ability to our advantage.
0:48:19 > 0:48:25Farmers have learned how to make the most of photosynthesis in all sorts of conditions
0:48:25 > 0:48:32and in modern glasshouses, they can manipulate the environment to increase production,
0:48:32 > 0:48:35often in ways that are quite surprising.
0:48:37 > 0:48:39SHEEP BLEATING
0:48:41 > 0:48:46The Netherlands is one of the world's smallest countries,
0:48:46 > 0:48:50yet it has become one of the world's biggest food exporters.
0:48:53 > 0:48:55In these vast greenhouses,
0:48:55 > 0:49:01commercial growers have learned to manipulate the building blocks of photosynthesis.
0:49:03 > 0:49:07They don't rely on sunlight to grow crops.
0:49:09 > 0:49:13They can make their own with the help of 3,500 light bulbs.
0:49:16 > 0:49:22When the sun goes down, the lights come on and the plants continue to grow.
0:49:24 > 0:49:26By changing the lighting conditions,
0:49:26 > 0:49:32they can bring forward the growing season of these peppers by four weeks.
0:49:33 > 0:49:38More light buys the plant more time to turn sugar into fruit.
0:49:43 > 0:49:50With sunlight guaranteed, this greenhouse produces 14 million peppers every year.
0:49:53 > 0:49:59Sunlight isn't the only part of photosynthesis that can be manipulated to our advantage.
0:49:59 > 0:50:01Thanks to a quirk of evolution,
0:50:01 > 0:50:06changing the levels of carbon dioxide can also have a dramatic effect.
0:50:06 > 0:50:11There have been times in the history of the Earth
0:50:11 > 0:50:15when the carbon dioxide levels were very different
0:50:15 > 0:50:21and as a result, plants have the capacity to use extra carbon dioxide to make more sugar
0:50:21 > 0:50:23and to produce bigger fruit.
0:50:29 > 0:50:35Commercial growers have been quick to exploit this legacy of our planet's past.
0:50:37 > 0:50:43Today, this Suffolk greenhouse produces 50% of all the tomatoes grown in Britain.
0:50:46 > 0:50:50The secret to more tomatoes is more carbon dioxide.
0:50:54 > 0:50:58Next door to the greenhouse is this factory.
0:50:58 > 0:51:00It generates two waste products.
0:51:00 > 0:51:04One is steam which escapes up these chimneys
0:51:04 > 0:51:07and the other is carbon dioxide,
0:51:07 > 0:51:12a greenhouse gas that you don't want to release into the atmosphere.
0:51:13 > 0:51:20So instead, this greenhouse gas gets pumped from the factory into...a greenhouse.
0:51:22 > 0:51:25These plastic tubes have tiny holes
0:51:25 > 0:51:30which deliver the gas to the leaves of the tomato plants.
0:51:34 > 0:51:39Give a tomato plant extra carbon dioxide and it produces more sugar
0:51:39 > 0:51:43which makes for a sweeter tomato which is good for us.
0:51:43 > 0:51:45It also doubles the yield
0:51:45 > 0:51:48which is good for the grower.
0:51:49 > 0:51:53By fine-tuning the environment of plants,
0:51:53 > 0:51:55we can grow more food.
0:51:58 > 0:52:04These commercial growers have got photosynthesis down to a fine art.
0:52:04 > 0:52:08They can manipulate it, but that's as far as it goes.
0:52:08 > 0:52:11Plants are still doing all the hard work.
0:52:18 > 0:52:25Turning water and carbon dioxide into leaves, seeds and fruits makes huge demands on a plant.
0:52:26 > 0:52:30To fuel this growth, it needs a reliable source of power.
0:52:31 > 0:52:35However different they are, wherever they come from,
0:52:35 > 0:52:42plants are all able to survive and grow because of their ability to harness energy from the sun.
0:52:48 > 0:52:53The amount of light energy converted by photosynthesis is staggering.
0:52:56 > 0:53:00In one year, all the plants on Earth generate enough energy
0:53:00 > 0:53:04to power human civilisation six times over.
0:53:06 > 0:53:10We now know a great deal about photosynthesis.
0:53:10 > 0:53:14We can manipulate it to make better crops and feed more people.
0:53:14 > 0:53:19But this is just the start. The next step is really exciting.
0:53:19 > 0:53:26And if science gets it right, it will alter lives for generations to come.
0:53:39 > 0:53:43At the University of Glasgow, Professor Lee Cronin is trying
0:53:43 > 0:53:47to recreate photosynthesis in his laboratory.
0:53:47 > 0:53:52Something that plants have been doing for more than a thousand million years,
0:53:52 > 0:53:56he is trying to do artificially in a decade.
0:53:58 > 0:54:03Plants use the sun's energy to split water into hydrogen and oxygen,
0:54:03 > 0:54:07two gases that could help make the fuels of the future.
0:54:09 > 0:54:13It's this process that Lee is trying to copy.
0:54:15 > 0:54:19This very thin electrode where you see all these very small bubbles
0:54:19 > 0:54:22is a platinum electrode where the hydrogen is coming off,
0:54:22 > 0:54:28and at this black electrode with the slightly bigger bubble is where the oxygen is being produced.
0:54:28 > 0:54:34- This normally happens inside a leaf, but here it's happening in this flask.- Exactly.
0:54:34 > 0:54:36'There's still a long way to go.
0:54:37 > 0:54:41'Lee can't split water using just light.
0:54:41 > 0:54:43'Not yet anyway.
0:54:43 > 0:54:46'He still needs a battery to power the process,
0:54:46 > 0:54:48'but the potential is enormous.'
0:54:48 > 0:54:55If we let this go long enough, the water in here would get less and less as it's being converted to the gas
0:54:55 > 0:54:59- and there'd be nothing left at the end.- How long would that take?
0:54:59 > 0:55:05- Probably... Well, at this rate, probably a few days.- Right. - So we don't need very much water.
0:55:05 > 0:55:08There's a huge amount of gas locked up in here.
0:55:08 > 0:55:14- But this is the critical first step of the photosynthesis story? - Yeah, exactly.
0:55:14 > 0:55:17Once we've perfected the first step, there is a critical part
0:55:17 > 0:55:23where we take carbon dioxide from the atmosphere and complete the story and turn the carbon dioxide
0:55:23 > 0:55:27into a fuel that we could put in an aeroplane or a car.
0:55:27 > 0:55:34So our family cars could start, in years to come, from a process like this with water being split?
0:55:34 > 0:55:37- There's every possibility. We're very excited about it.- Wow!
0:55:37 > 0:55:42'So he should be. The prize is clean and limitless energy.
0:55:42 > 0:55:48'No wonder labs like this all over the world are working hard to crack the problem.'
0:55:48 > 0:55:54If we get this right, if we're able to understand and learn from photosynthesis in such a way
0:55:54 > 0:55:59that we can surpass evolution if you like and make an even better device
0:55:59 > 0:56:04to take light energy, carbon dioxide and water and produce a fuel,
0:56:04 > 0:56:10then this is going to have massive ramifications for our society and our environment.
0:56:24 > 0:56:26Lee's work is impressive,
0:56:26 > 0:56:30but it shows how sophisticated photosynthesis is
0:56:30 > 0:56:34and scientists will be hard pressed to replicate it.
0:56:34 > 0:56:38The thought that it may provide an alternative source of energy
0:56:38 > 0:56:41confirms the awesome power of photosynthesis.
0:56:44 > 0:56:50To see the power of photosynthesis in action, take a look at these images from NASA.
0:56:50 > 0:56:54They show how photosynthesis varies across the globe
0:56:54 > 0:56:57with the ebb and flow of the seasons.
0:56:57 > 0:56:59That's not the whole story.
0:56:59 > 0:57:02What's fascinating is the oceans.
0:57:04 > 0:57:06They're glowing green.
0:57:06 > 0:57:13That's because half of the world's photosynthesis takes place not on the land, but in the sea.
0:57:15 > 0:57:20How close are we to understanding all there is to know about photosynthesis?
0:57:20 > 0:57:27We understand the broad principles of how photosynthesis works, but the real fine detail still eludes us.
0:57:27 > 0:57:32We can put a man on the moon, but we can't mimic photosynthesis.
0:57:39 > 0:57:45Botany has come a long way since the time when people believed plants eat soil.
0:57:47 > 0:57:51Today, we can feed more of the world's population.
0:57:51 > 0:57:55Tomorrow, we may even find a way to fuel our planet.
0:57:57 > 0:57:59And it's all down to photosynthesis,
0:57:59 > 0:58:04for me, the most remarkable and important process on Earth.
0:58:06 > 0:58:09Next time on Botany: A Blooming History...
0:58:10 > 0:58:15I'll be looking at how botanists puzzled over the colours of snapdragons,
0:58:15 > 0:58:19investigated the mysteries of wild maize
0:58:19 > 0:58:24and developed a brand-new science - plant genetics.
0:58:45 > 0:58:49Subtitles by Subtext for Red Bee Media Ltd 2011
0:58:49 > 0:58:52Email subtitling@bbc.co.uk