1 00:00:10,160 --> 00:00:12,240 'It's nearly summer 2 00:00:12,240 --> 00:00:16,440 'and the garden is bursting with life. 3 00:00:16,440 --> 00:00:21,680 'As a botanist, I'm fascinated by what makes plants grow. 4 00:00:21,680 --> 00:00:26,120 'For instance, to produce all this colour and diversity 5 00:00:26,120 --> 00:00:30,360 'you need just a few minerals and three basic ingredients.' 6 00:00:32,880 --> 00:00:36,560 Water, sunlight and carbon dioxide, 7 00:00:36,560 --> 00:00:40,000 the stuff that I'm breathing out right now. 8 00:00:40,000 --> 00:00:42,880 And that is all. Nothing else. 9 00:00:47,400 --> 00:00:54,760 Plants turn these ingredients into food for growth and a waste product we find very useful - oxygen. 10 00:00:58,920 --> 00:01:01,000 It sounds simple, 11 00:01:01,000 --> 00:01:06,600 but this process is one of the most fascinating and complicated in the whole of science. 12 00:01:06,600 --> 00:01:09,280 It's called photosynthesis. 13 00:01:13,520 --> 00:01:18,720 'It'll take the pioneers of botany over 400 years to work out 14 00:01:18,720 --> 00:01:21,360 'why a leaf needs sunlight, 15 00:01:21,360 --> 00:01:24,760 'what role water plays 16 00:01:24,760 --> 00:01:29,760 'and why a plant can't exist without carbon dioxide. 17 00:01:32,120 --> 00:01:37,120 'Today photosynthesis is at the forefront of scientific research.' 18 00:01:37,120 --> 00:01:41,040 If we get this right and learn from photosynthesis, 19 00:01:41,040 --> 00:01:47,640 we should be able to produce very quickly a liquid fuel for cars... No more gasoline, no more diesel? 20 00:01:47,640 --> 00:01:50,000 No more fossil fuel. 21 00:01:50,000 --> 00:01:57,360 'Photosynthesis is taking place right now in every leaf of every plant.' 22 00:01:57,360 --> 00:02:00,480 I find that amazing. 23 00:02:30,800 --> 00:02:36,440 'The University of Oxford Botanic Garden is the oldest in Britain. 24 00:02:36,440 --> 00:02:39,520 'I've been Director here for 22 years 25 00:02:39,520 --> 00:02:43,120 'and one of the great things about the job 26 00:02:43,120 --> 00:02:45,600 'is that I get to live here.' 27 00:02:49,760 --> 00:02:55,680 When the gates are locked, this enchanting place becomes my back garden. 28 00:03:13,240 --> 00:03:18,360 It took botanists a long time to understand the complex process 29 00:03:18,360 --> 00:03:22,800 that transforms a seed into a fully-grown tree. 30 00:03:22,800 --> 00:03:29,080 Any scientific journey will have twists and turns. Working out how plants grow was no exception. 31 00:03:38,360 --> 00:03:43,160 This is the 1648 catalogue for the Botanic Garden. 32 00:03:43,160 --> 00:03:49,360 "An English list of the trees and plants...with the Latin names added there unto." 33 00:03:49,360 --> 00:03:51,440 Very grand. 34 00:03:51,440 --> 00:03:58,360 It only contains about 1,500 species, but it indicates the growing interest in botany 35 00:03:58,360 --> 00:04:05,080 and it was around this time that some inquisitive minds began to ask, "How do plants grow?" 36 00:04:08,880 --> 00:04:13,720 One of the first to investigate the natural world is an alchemist. 37 00:04:14,720 --> 00:04:17,640 His name is Jan Baptist van Helmont. 38 00:04:21,480 --> 00:04:24,320 'He dabbles in medicine and magic, 39 00:04:24,320 --> 00:04:28,240 'a dangerous combination in the 17th century. 40 00:04:29,280 --> 00:04:33,240 'Science is seen as a threat to God and His creation. 41 00:04:36,000 --> 00:04:41,800 'So when van Helmont suggests that plants could have miraculous healing properties, 42 00:04:41,800 --> 00:04:47,920 'he's asking for trouble. And it's not long before trouble comes knocking at his door.' 43 00:04:55,160 --> 00:05:00,760 In March, 1634, agents of the Spanish Inquisition call at a house in Brussels. 44 00:05:00,760 --> 00:05:05,560 They take 55-year-old Jan Baptist van Helmont away for questioning. 45 00:05:11,120 --> 00:05:15,360 'They interrogate him and put him under house arrest. 46 00:05:15,360 --> 00:05:19,000 'They accuse him of violating God's law.' 47 00:05:19,000 --> 00:05:23,840 His crime? The scientific study of plants and other phenomena. 48 00:05:25,920 --> 00:05:29,920 'Van Helmont is lucky to escape with his life. 49 00:05:32,200 --> 00:05:38,080 'While under house arrest, he starts thinking about a question that's always intrigued him. 50 00:05:39,040 --> 00:05:41,480 'How do plants grow? 51 00:05:48,680 --> 00:05:53,520 'For over 2,000 years, people believed plants grew by eating soil. 52 00:05:53,520 --> 00:05:57,520 'Van Helmont wants to know if this is true, 53 00:05:59,120 --> 00:06:01,520 'so he devises an experiment, 54 00:06:02,760 --> 00:06:08,600 'one that hopefully won't attract the attention of the Spanish Inquisition.' 55 00:06:08,600 --> 00:06:13,240 Van Helmont used a willow tree and a wagon full of soil. 56 00:06:13,240 --> 00:06:17,400 I'm using a bay tree and less soil, but the principle's the same. 57 00:06:17,400 --> 00:06:22,920 The first thing Van Helmont did was to weigh his tree and note its weight. 58 00:06:29,080 --> 00:06:31,240 Next he weighed the soil, 59 00:06:31,240 --> 00:06:35,960 dry soil because he didn't want water to affect its weight. 60 00:06:40,800 --> 00:06:43,640 Van Helmont then planted his tree, 61 00:06:46,680 --> 00:06:48,720 watered it 62 00:06:51,840 --> 00:06:54,000 and his experiment was ready to go. 63 00:07:01,160 --> 00:07:07,640 'Each of my bay trees represents a year in the growth of the willow tree that van Helmont planted.' 64 00:07:09,720 --> 00:07:13,800 He watched it grow for not one year or two years, 65 00:07:13,800 --> 00:07:17,360 but he tended the tree for five years. 66 00:07:17,360 --> 00:07:19,400 And then he re-weighed it. 67 00:07:23,040 --> 00:07:27,360 After five years, the tree has gained a hefty 12 stone. 68 00:07:30,800 --> 00:07:34,840 'The van Helmont dries and weighs the soil. 69 00:07:34,840 --> 00:07:39,320 'The soil weighs almost exactly the same as it did five years ago.' 70 00:07:42,320 --> 00:07:48,240 He concludes the tree has grown not by eating soil, but by drinking water. 71 00:07:58,800 --> 00:08:03,240 After all this effort, van Helmont decides not to publish his results. 72 00:08:03,240 --> 00:08:05,720 He is scared. 73 00:08:06,800 --> 00:08:09,600 And with good reason. 74 00:08:09,600 --> 00:08:13,680 'His experiment relies on evidence, not faith. 75 00:08:13,680 --> 00:08:19,760 'He doesn't want to risk getting on the wrong side of the authorities again, 76 00:08:19,760 --> 00:08:24,080 'so his results are only published after his death.' 77 00:08:26,640 --> 00:08:30,720 For all his personal sacrifice, van Helmont was wrong. 78 00:08:30,720 --> 00:08:36,200 Water IS important for the growth of plants, but it is far from the whole story. 79 00:08:39,600 --> 00:08:44,360 'He misses something fundamental and he isn't the only one. 80 00:08:48,160 --> 00:08:52,560 'I've found a document at my Botanic Garden which shows 81 00:08:52,560 --> 00:08:56,840 'how little people in the 17th century knew about plants.' 82 00:08:58,960 --> 00:09:05,160 Now look at this. This is a plan of the Oxford Botanic Garden in 1675. 83 00:09:05,160 --> 00:09:11,240 And up here in the top right-hand corner is a new addition, a house for plants. 84 00:09:11,240 --> 00:09:15,600 This was the pride and joy of the Director back then. 85 00:09:15,600 --> 00:09:19,640 His baby, his big 17th-century project. 86 00:09:21,280 --> 00:09:28,200 But if you look closely at it, you can see that there's a reason why this wasn't a great success. 87 00:09:29,240 --> 00:09:32,640 There's something missing from this house. 88 00:09:32,640 --> 00:09:37,200 And it's the fact that there are virtually no windows 89 00:09:37,200 --> 00:09:40,440 and those that are there are tiny. 90 00:09:40,440 --> 00:09:44,440 Hardly any windows and no glass in the roof. 91 00:09:44,440 --> 00:09:48,080 They were never going to grow much in here. 92 00:09:48,080 --> 00:09:52,120 What is really interesting about this is that it clearly shows 93 00:09:52,120 --> 00:09:59,040 that 17th-century botanists had not made the connection between the growth of plants and light. 94 00:10:01,520 --> 00:10:06,360 'It sounds obvious to us today, but back then many people believed 95 00:10:06,360 --> 00:10:08,920 'that leaves grew by God's will. 96 00:10:09,960 --> 00:10:14,480 'So suggesting sunlight plays a part is pretty radical. 97 00:10:15,520 --> 00:10:20,200 'It's an important step on the road to understanding photosynthesis.' 98 00:10:38,560 --> 00:10:44,520 In the spring of 1779, a brilliant Dutch physician took a carriage from London 99 00:10:44,520 --> 00:10:48,640 to take the air in the English countryside. 100 00:10:48,640 --> 00:10:54,600 He didn't know it yet, but this pioneering doctor was going to open a new chapter 101 00:10:54,600 --> 00:10:59,200 in the story of how plants grow. His name was Jan Ingenhousz. 102 00:11:10,000 --> 00:11:12,080 As a young man, 103 00:11:12,080 --> 00:11:17,840 he had a gift for science and for medicine, inspired by his father's work as an apothecary, 104 00:11:17,840 --> 00:11:20,560 making remedies for ailments. 105 00:11:20,560 --> 00:11:26,520 His leap to fame came not from studying plants. He was a smallpox inoculator. 106 00:11:31,080 --> 00:11:33,440 'It's a well-paid job, 107 00:11:33,440 --> 00:11:37,520 'so Ingenhousz can afford to rent a plush villa 108 00:11:37,520 --> 00:11:43,520 'He exchanges the distraction of the city for the tranquillity of the countryside 109 00:11:43,520 --> 00:11:47,600 'with a plan to write a book about smallpox, 110 00:11:47,600 --> 00:11:52,160 'but it's the countryside that soon becomes the distraction.' 111 00:11:55,720 --> 00:12:00,200 It wasn't long before Ingenhousz put his book on the back burner. 112 00:12:00,200 --> 00:12:06,240 Instead, he turned his attention to the countryside and the plants that flourished all around him 113 00:12:06,240 --> 00:12:12,880 and he embarked on a series of experiments that would revolutionise our understanding of plants. 114 00:12:12,880 --> 00:12:19,040 'In the late 18th century, it's the fashion among scientists to investigate gases. 115 00:12:19,040 --> 00:12:24,240 'One eminent scientist suggests that plants give off gas. 116 00:12:25,280 --> 00:12:27,920 'Ingenhousz sets up an experiment 117 00:12:27,920 --> 00:12:31,040 'to find out if this is true.' 118 00:12:31,040 --> 00:12:37,040 His test was simple. He collected leaves from his garden and he put them in water. 119 00:12:37,040 --> 00:12:40,760 Ingenhousz then observed his experiment. 120 00:12:40,760 --> 00:12:42,800 When watching plants, 121 00:12:42,800 --> 00:12:45,800 patience is important. 122 00:12:54,560 --> 00:12:58,600 'Ingenhousz believes that if he puts plants under water, 123 00:12:58,600 --> 00:13:02,960 'any gas given off will rise to the surface as bubbles. 124 00:13:04,120 --> 00:13:08,080 'This will give him a clue as to how plants grow.' 125 00:13:13,360 --> 00:13:19,360 As much as he tried, he could not get any of his submerged leaves to give off any gas 126 00:13:19,360 --> 00:13:23,560 until one day his attention is caught by a sample 127 00:13:23,560 --> 00:13:26,080 in a shaft of sunlight. 128 00:13:26,080 --> 00:13:30,000 Once again, Ingenhousz observes his experiment. 129 00:13:39,520 --> 00:13:43,560 After just 10 minutes, something really interesting is happening. 130 00:13:43,560 --> 00:13:47,920 The sample in the shade, same old story, nothing. 131 00:13:47,920 --> 00:13:54,080 But the sample in the shaft of light is different. Tiny bubbles of gas are emerging from the leaves. 132 00:13:54,080 --> 00:13:57,520 For Ingenhousz, this was a really exciting moment. 133 00:13:58,720 --> 00:14:05,400 For the first time, he had made the connection between sunlight and the production of gas in leaves. 134 00:14:07,600 --> 00:14:13,200 'Ingenhousz proves that plants exposed to sunlight do indeed give off a gas. 135 00:14:13,200 --> 00:14:16,760 'Now he wants to find out what that gas is.' 136 00:14:25,160 --> 00:14:31,000 The tiny bubbles of gas released by the leaves have accumulated in the top of the jar. 137 00:14:31,000 --> 00:14:36,200 If I take this glowing splint and put it in there, it re-ignites. 138 00:14:37,240 --> 00:14:39,800 Indicating the presence of oxygen. 139 00:14:46,320 --> 00:14:50,360 'Sunlight triggers the release of oxygen from leaves. 140 00:14:50,360 --> 00:14:54,560 'Ingenhousz knows it's a significant discovery. 141 00:14:54,560 --> 00:14:57,440 'He has to be sure he's right. 142 00:14:58,760 --> 00:15:03,240 'There follows a summer of frenzied activity at the villa. 143 00:15:05,880 --> 00:15:10,440 'The doctor turned botanist repeats the experiment over and over again.' 144 00:15:14,280 --> 00:15:19,560 Ingenhousz used all sorts of leaves from plants in his garden. 145 00:15:19,560 --> 00:15:23,240 Holly, ash, nettles and oak. 146 00:15:23,240 --> 00:15:29,320 Each one he immersed in water and placed one in the sunlight and one in the shade. 147 00:15:31,000 --> 00:15:37,080 He even visited the King's gardener at Kew who gave him leaves of exotic plants like cocoa. 148 00:15:37,080 --> 00:15:41,520 Every leaf that was placed in the sunshine bubbled. 149 00:15:44,880 --> 00:15:51,520 'Ingenhousz wants to know if it's the sun's light or its heat that causes the gas to be released. 150 00:15:51,520 --> 00:15:56,200 'So he puts leaves in water near an open fire and watches them. 151 00:15:56,200 --> 00:16:00,640 'When no bubbles are given off, he knows he's right. 152 00:16:00,640 --> 00:16:07,120 'It's the sun's light, not its heat that's important for the production of gas in plants. 153 00:16:08,200 --> 00:16:14,000 'He then repeats his experiment with different leaves and gets the same result.' 154 00:16:15,240 --> 00:16:19,920 Ingenhousz began to realise that this process was universal. 155 00:16:21,560 --> 00:16:25,560 'His holiday has taken an unexpected turn. 156 00:16:25,560 --> 00:16:28,240 'He arrived a successful doctor, 157 00:16:28,240 --> 00:16:34,960 'he leaves a pioneering botanist, having unlocked a key part of photosynthesis. 158 00:16:41,480 --> 00:16:47,960 'Who would have thought that plants produce a waste product that makes all human and animal life possible? 159 00:16:47,960 --> 00:16:50,360 'Oxygen.' 160 00:17:02,160 --> 00:17:07,640 It would be 100 years before botany took another leap forward 161 00:17:07,640 --> 00:17:12,880 and this advance was made by one of the giants of science, 162 00:17:12,880 --> 00:17:17,840 a man who deserves to be as well-known as Darwin. 163 00:17:23,680 --> 00:17:26,560 'Julius Sachs was born in 1832. 164 00:17:26,560 --> 00:17:32,120 'He has a passion for plants that would come to dominate his life. 165 00:17:36,520 --> 00:17:40,960 'As a schoolboy, Sachs is fascinated by nature.' 166 00:17:42,200 --> 00:17:47,200 He wasn't interested in science, not then. He was just mad about plants. 167 00:17:49,960 --> 00:17:55,680 'Every day before school, he collects and carefully records the local flora. 168 00:17:56,720 --> 00:18:01,480 'As a botanist, I completely understand where he's coming from. 169 00:18:01,480 --> 00:18:05,080 'That desire to surround yourself with plants. 170 00:18:05,080 --> 00:18:09,560 'If you get the bug early, it never leaves you.' 171 00:18:10,720 --> 00:18:15,760 So when Sachs went out into the countryside in Germany to collect flowers, 172 00:18:15,760 --> 00:18:20,160 he was undertaking a very personal activity, 173 00:18:21,280 --> 00:18:27,720 but at the same time joining a tradition that goes back at least four centuries. 174 00:18:27,720 --> 00:18:32,000 You're not just collecting this specimen for yourself, 175 00:18:32,000 --> 00:18:38,240 but for a worldwide record of where particular plants were growing on a particular day. 176 00:18:38,240 --> 00:18:44,080 And around the world there are millions of specimens like this 177 00:18:44,080 --> 00:18:48,280 put together and collected by people like Sachs. 178 00:18:48,280 --> 00:18:51,880 I find it a very satisfying activity. 179 00:18:51,880 --> 00:18:53,760 And... 180 00:18:53,760 --> 00:18:59,400 I'm sure that Sachs found it equally peaceful and rewarding. 181 00:19:00,600 --> 00:19:04,640 'It's a passion that Sachs pursues as he grows up, 182 00:19:04,640 --> 00:19:10,560 'but these idyllic days spent collecting plants are about to come to an abrupt end.' 183 00:19:14,280 --> 00:19:18,600 When Sachs was 17, personal tragedy struck 184 00:19:18,600 --> 00:19:24,360 with the death of his mother, father and one of his brothers in the same year. 185 00:19:26,120 --> 00:19:29,120 He drops out of school. 186 00:19:29,120 --> 00:19:33,160 'Without his parents, the young Sachs is penniless. 187 00:19:33,160 --> 00:19:37,920 'Then a family friend offers him a job at the University of Prague.' 188 00:19:39,200 --> 00:19:41,440 His professor drove him hard. 189 00:19:43,120 --> 00:19:47,040 'He's forced to work long hours in the laboratory. 190 00:19:48,560 --> 00:19:54,640 'The job gives the young Sachs an understanding of the rigorous methodology required of a scientist. 191 00:19:57,760 --> 00:20:04,760 'He has just enough money to live, but not nearly enough time to pursue his real passion - 192 00:20:04,760 --> 00:20:06,600 'plants. 193 00:20:08,280 --> 00:20:12,080 'He turns to drugs to help him stay awake, 194 00:20:13,120 --> 00:20:17,880 'working for his employer during the day and for himself at night. 195 00:20:19,880 --> 00:20:22,800 'Over the next 20 years, 196 00:20:22,800 --> 00:20:29,160 'Sachs conducts thousands of experiments and writes up his results in meticulous detail.' 197 00:20:30,560 --> 00:20:38,080 Sachs toiled for many years before producing this, his Textbook of Experimental Plant Physiology. 198 00:20:40,160 --> 00:20:47,040 It's all in here - the role of light, the need for gases, the need for water. 199 00:20:50,160 --> 00:20:56,520 This book became the standard textbook for plant biologists in Europe. 200 00:20:56,520 --> 00:20:59,080 It was translated into English 201 00:20:59,080 --> 00:21:03,080 and it is a quite, quite beautiful piece of work. 202 00:21:04,920 --> 00:21:07,520 Wonderful, wonderful detail. 203 00:21:07,520 --> 00:21:10,320 It's a true magnum opus. 204 00:21:11,320 --> 00:21:12,800 Phenomenal. 205 00:21:18,160 --> 00:21:21,160 'This book is the making of him. 206 00:21:21,160 --> 00:21:23,600 'Offers of work flood in. 207 00:21:31,640 --> 00:21:35,720 'I've come to Wurzburg in Central Germany. 208 00:21:37,520 --> 00:21:43,440 'It's here that Sachs is appointed head of Europe's top botanical institute in 1868. 209 00:21:45,080 --> 00:21:48,000 'He's just 36 years old.' 210 00:21:50,360 --> 00:21:57,240 So from his undeniably humble origins, Sachs arrives in Wurzburg as the leading botanist in Europe. 211 00:21:57,240 --> 00:22:02,640 He's the head of a big university department with his own research group 212 00:22:02,640 --> 00:22:08,680 and he drives that research group with the same obsession that he drove himself 213 00:22:08,680 --> 00:22:13,640 and he still relies on drugs to keep himself going. 214 00:22:18,160 --> 00:22:23,160 But he was still driven. He still wanted to know more. 215 00:22:23,160 --> 00:22:27,200 He still wanted to know what made plants grow, 216 00:22:27,200 --> 00:22:30,800 how they took that light and what they did with it. 217 00:22:32,760 --> 00:22:39,440 'Only now he has the reputation, money and resources to tackle these big questions. 218 00:22:40,720 --> 00:22:44,840 'This time he's the one driving his colleagues hard. 219 00:22:51,200 --> 00:22:56,960 'Today there's an institute dedicated to Sachs at the University of Wurzburg. 220 00:22:56,960 --> 00:23:00,880 'Professor Markus Riederer is the Director.' 221 00:23:00,880 --> 00:23:02,360 Wow! 222 00:23:03,400 --> 00:23:08,840 These are his paintings he did himself for using them in lectures. 223 00:23:08,840 --> 00:23:11,400 So this is 19th-century Powerpoint! 224 00:23:11,400 --> 00:23:14,240 It is! Only rather more beautiful. 225 00:23:14,240 --> 00:23:19,840 When you step back to where the students saw it, it looks beautifully detailed. 226 00:23:19,840 --> 00:23:24,560 The right scale. Indeed. That's terrific. 227 00:23:24,560 --> 00:23:29,240 So what else have you got? Is this his microscope? It is, yeah. 228 00:23:29,240 --> 00:23:33,200 It says Sachs on it. That's tremendous. 229 00:23:33,200 --> 00:23:39,280 So down here, are these the accounts for the laboratory? No, it's his private accounts. 230 00:23:39,280 --> 00:23:43,720 He had a family - a wife and three children. Did they ever see him? 231 00:23:43,720 --> 00:23:47,440 I cannot believe that. He always worked. 232 00:23:47,440 --> 00:23:51,680 'His personal accounts include a few surprises.' 233 00:23:52,880 --> 00:23:54,960 That's cocaine. 234 00:23:54,960 --> 00:23:59,600 Cocaine. OK. In his accounts. It was legal then. 235 00:23:59,600 --> 00:24:01,560 Oh, OK! 236 00:24:01,560 --> 00:24:07,160 So did that keep him going 14 hours a day? Exactly. To produce this work. Ja, ja. 237 00:24:09,360 --> 00:24:14,720 'Sachs' desire to understand what makes plants grow is all-consuming. 238 00:24:14,720 --> 00:24:19,440 'He knows sunlight produces gas from leaves. This gas is oxygen. 239 00:24:19,440 --> 00:24:24,200 'What he doesn't know is why sunlight is so important. 240 00:24:25,680 --> 00:24:30,520 'Professor Riederer recreates one of Sachs' best-known experiments.' 241 00:24:30,520 --> 00:24:35,560 I have a leaf which has been in the light all day. A normal leaf. 242 00:24:35,560 --> 00:24:39,400 That's a normal leaf that has seen hours of light. 243 00:24:39,400 --> 00:24:45,640 And Sachs wanted to find out what was inside it. Exactly. Enabling it to grow. Exactly. 244 00:24:50,000 --> 00:24:56,920 'By the 19th century, botanists knew that a plant's growth wasn't down to water and sunlight alone. 245 00:24:56,920 --> 00:25:02,480 'Every green plant stores its energy by making something called starch. 246 00:25:02,480 --> 00:25:09,800 'It's a vital component of the human diet and it's the power at the heart of a growing plant. 247 00:25:11,320 --> 00:25:17,600 'Knowing this, he sets out to discover the role sunlight plays in the production of starch. 248 00:25:17,600 --> 00:25:23,440 'He strips the green colour from a leaf and applies iodine to the white leaf. 249 00:25:24,760 --> 00:25:30,480 'He knows that iodine will react with starch produced in the leaf, turning it black.' 250 00:25:32,800 --> 00:25:36,760 The starch is stained now. It certainly is. 251 00:25:36,760 --> 00:25:38,840 Hey, presto! 252 00:25:38,840 --> 00:25:45,560 So this leaf, which had been grown normally in the sunlight, has gone black because it's full of starch. 253 00:25:45,560 --> 00:25:47,040 Yeah. 254 00:25:47,040 --> 00:25:50,720 'Now Sachs tries the experiment again. 255 00:25:50,720 --> 00:25:56,360 'This time he uses a leaf that has seen no sunlight for 12 hours. 256 00:25:56,360 --> 00:26:00,240 'Again, he strips the green colour out of the leaf. 257 00:26:03,800 --> 00:26:07,560 'This time when the iodine is added, nothing happens. 258 00:26:07,560 --> 00:26:10,480 'The leaf stays completely white. 259 00:26:10,480 --> 00:26:14,880 'Having been left in the dark, it contains no starch. 260 00:26:17,520 --> 00:26:20,200 'Sachs carries out one final test. 261 00:26:20,200 --> 00:26:26,160 'Part of a leaf is covered up while another part of the same leaf is left uncovered.' 262 00:26:28,600 --> 00:26:31,120 We have our version of this. 263 00:26:34,160 --> 00:26:37,200 'He then places the leaf in the sunlight. 264 00:26:41,320 --> 00:26:47,400 'If Sachs is right, only those parts of the leaf exposed to the sun should produce starch.' 265 00:26:50,400 --> 00:26:54,840 Part of this leaf should have starch in, the bit that was illuminated. 266 00:26:54,840 --> 00:26:57,360 And the bit in the shade should not. 267 00:26:57,360 --> 00:27:01,800 This is an exciting moment, isn't it? It is exciting. It is. 268 00:27:03,160 --> 00:27:05,120 So on goes the iodine. 269 00:27:08,520 --> 00:27:14,240 We're starting to see some of the tissue... Ah! 270 00:27:14,240 --> 00:27:18,200 Our "Light" is coming out! Now look at that! 271 00:27:18,200 --> 00:27:24,800 It's back to front, but you can already see that the part of the stencil 272 00:27:24,800 --> 00:27:30,600 where the light went through, the leaf is black. So starch has only been formed 273 00:27:30,600 --> 00:27:36,640 on the part of the leaf that was exposed to the light. It's like photography. It is! 274 00:27:36,640 --> 00:27:40,840 That wonderful moment in a darkroom when the picture appears. 275 00:27:40,840 --> 00:27:43,200 So there you are. 276 00:27:43,200 --> 00:27:50,080 Fantastic. And you've got a beautiful demonstration, very elegant, very simple, 277 00:27:50,080 --> 00:27:55,880 that light equals starch, shade equals no starch. That's right. 278 00:28:04,160 --> 00:28:09,200 This was a breakthrough. It was a monumental quantum step up 279 00:28:09,200 --> 00:28:12,680 in our understanding of how plants grow 280 00:28:12,680 --> 00:28:19,000 and it's one of those experiments when you think, "Why didn't I think of that? Why didn't anybody else?" 281 00:28:19,000 --> 00:28:21,960 The fact that Sachs did it 282 00:28:23,840 --> 00:28:29,240 shows just how he was so far above his contemporaries 283 00:28:29,240 --> 00:28:33,440 in plant science, in botany at that time. 284 00:28:40,120 --> 00:28:42,560 'Sachs doesn't stop there. 285 00:28:42,560 --> 00:28:46,400 'He wants to find where in the plant the starch is produced.' 286 00:28:52,160 --> 00:28:58,200 Sometimes science needs new tools to develop and botany was no exception. 287 00:28:58,200 --> 00:29:03,920 When, in the mid-19th century, a new generation of microscopes became available, 288 00:29:03,920 --> 00:29:07,720 Sachs was able to look right inside the leaf. 289 00:29:08,800 --> 00:29:13,440 When he looked down the lens of the microscope, 290 00:29:13,440 --> 00:29:19,320 Sachs could see inside each cell and it must have been as exciting then as it is now. 291 00:29:19,320 --> 00:29:22,440 What he saw inside the cells 292 00:29:22,440 --> 00:29:25,600 were small structures. 293 00:29:26,640 --> 00:29:28,720 Solid structures. 294 00:29:28,720 --> 00:29:33,600 And he realised that this is where the starch was being produced. 295 00:29:33,600 --> 00:29:38,440 And he had found the factory that fuelled the growth of the plant. 296 00:29:38,440 --> 00:29:43,480 And these small structures in each cell are called chloroplasts. 297 00:29:44,800 --> 00:29:50,240 And the energy produced within these chloroplasts 298 00:29:50,240 --> 00:29:53,880 is what goes on to fuel the growth of the plant. 299 00:29:53,880 --> 00:29:58,560 Not only that, but the production of flowers, seeds, 300 00:29:58,560 --> 00:30:01,280 fruit and the next generation. 301 00:30:03,680 --> 00:30:06,400 Now, 150 years later, 302 00:30:06,400 --> 00:30:12,040 we have microscopes that enable us to look inside living cells... 303 00:30:13,160 --> 00:30:16,760 ..and reveal what's going on inside them. 304 00:30:17,800 --> 00:30:20,680 Sachs would have been amazed to see 305 00:30:20,680 --> 00:30:25,240 that the chloroplasts are not sitting in the cells 306 00:30:25,240 --> 00:30:29,640 inactive and static, as they were on his microscope slide, 307 00:30:29,640 --> 00:30:33,040 but they are jostling for position, 308 00:30:33,040 --> 00:30:36,480 so that the production of starch is maximised 309 00:30:36,480 --> 00:30:38,560 as the light changes. 310 00:30:38,560 --> 00:30:42,800 It's the most amazingly efficient production system in nature. 311 00:30:44,560 --> 00:30:48,480 As sunlight hits a leaf, the chloroplasts leap into action. 312 00:30:49,560 --> 00:30:53,360 When this short clip is repeated and speeded up, 313 00:30:53,360 --> 00:30:58,640 we can see these chloroplasts vying with each other to grab the sun's rays. 314 00:31:00,720 --> 00:31:07,440 This wonderful dance of the chloroplasts is going on all around us 315 00:31:07,440 --> 00:31:10,240 in what seem like static leaves 316 00:31:10,240 --> 00:31:16,720 and the plant is doing it to ensure that it captures just the right amount of light - 317 00:31:16,720 --> 00:31:19,640 not too little and not too much. 318 00:31:21,640 --> 00:31:26,600 It would have been wonderful to be able to show this to Sachs, 319 00:31:26,600 --> 00:31:30,720 so that he could see that the chloroplasts that he observed... 320 00:31:31,800 --> 00:31:36,720 ..are moving in this quite beautiful way. 321 00:31:38,840 --> 00:31:43,000 Plants produce sugars which they store in the form of starch. 322 00:31:43,000 --> 00:31:46,960 Sachs shows where in the plant this happens, 323 00:31:46,960 --> 00:31:49,640 how in fact a plant grows. 324 00:31:51,760 --> 00:31:57,560 Sachs would have been astonished to see what happens inside this potato cell. 325 00:31:58,600 --> 00:32:02,200 To begin with, there's no sign of starch. 326 00:32:03,800 --> 00:32:09,720 Yet just after a few hours sitting in the sunlight, the cell is packed full of starch grains. 327 00:32:15,400 --> 00:32:22,920 In just over 200 years, the pioneers of botany have cracked some of the big questions of photosynthesis. 328 00:32:25,920 --> 00:32:28,720 They knew that plants don't eat soil, 329 00:32:28,720 --> 00:32:31,360 water and sunlight drive growth. 330 00:32:31,360 --> 00:32:37,040 They had also worked out that leaves give off a gas when exposed to the sun. 331 00:32:37,040 --> 00:32:39,640 That gas is oxygen. 332 00:32:42,400 --> 00:32:48,600 And thanks to a devastatingly simple experiment, they knew that plants use sunlight to produce sugars, 333 00:32:48,600 --> 00:32:52,000 a source of energy that gets stored as starch. 334 00:32:54,720 --> 00:33:00,480 All in all, a pretty impressive body of work for the fledgling science of botany. 335 00:33:00,480 --> 00:33:03,000 There is still something missing. 336 00:33:03,000 --> 00:33:06,320 Without it, photosynthesis is impossible. 337 00:33:06,320 --> 00:33:09,040 And it's in the very air we breathe. 338 00:33:10,480 --> 00:33:12,600 Carbon dioxide. 339 00:33:12,600 --> 00:33:16,920 When botanists used microscopes to examine the surface of leaves... 340 00:33:18,040 --> 00:33:22,280 ..they discovered something rather surprising. 341 00:33:26,720 --> 00:33:31,840 The underside of a leaf is covered with what looks like tiny pores. 342 00:33:31,840 --> 00:33:36,040 Modern microscopes show these in amazing detail. 343 00:33:37,920 --> 00:33:41,960 They're called stomata and it's through these tiny openings 344 00:33:41,960 --> 00:33:46,280 that plants take in carbon dioxide from the air around them. 345 00:33:48,680 --> 00:33:51,440 These stomata can open and close, 346 00:33:51,440 --> 00:33:57,280 thereby constantly regulating the amount of carbon dioxide getting into the plant. 347 00:34:03,120 --> 00:34:08,760 I'd like to think that a breath I exhaled 30 years ago now exists in the bark of this tree. 348 00:34:11,320 --> 00:34:13,680 There is a direct link 349 00:34:13,680 --> 00:34:17,280 between our lives and the lives of plants. 350 00:34:18,840 --> 00:34:23,000 We give plants carbon dioxide to fuel their growth... 351 00:34:24,120 --> 00:34:28,040 ..and they give us the oxygen we need to survive. 352 00:34:30,160 --> 00:34:35,000 Botanists in the 19th century knew that plants absorbed carbon dioxide. 353 00:34:35,000 --> 00:34:41,960 It wasn't until well into the 20th century that they found out what the plant did with it. 354 00:34:41,960 --> 00:34:47,440 It's the last major piece in the photosynthesis puzzle to be solved. 355 00:35:09,360 --> 00:35:13,240 Take a look at this photograph from the 1940s. 356 00:35:13,240 --> 00:35:19,040 It shows two men examining a camera, both of them scientists at the top of their game, 357 00:35:19,040 --> 00:35:21,920 nothing unusual in it at all. 358 00:35:21,920 --> 00:35:26,600 Except behind this photograph is a story of betrayal 359 00:35:26,600 --> 00:35:31,320 and a bitter feud that would last for four decades. 360 00:35:33,360 --> 00:35:36,600 'The man in the white shirt is Andrew Benson. 361 00:35:38,600 --> 00:35:44,600 'Benson is responsible for one of the most important discoveries in the story of photosynthesis. 362 00:35:44,600 --> 00:35:47,600 'His boss is Melvin Calvin, 363 00:35:47,600 --> 00:35:49,920 'a brilliant chemist. 364 00:35:51,000 --> 00:35:55,760 'Both men are working at the University of California at Berkeley. 365 00:35:56,880 --> 00:36:00,720 'Their research is focused on one question - 366 00:36:00,720 --> 00:36:04,800 'what does a plant do with carbon dioxide? 367 00:36:09,920 --> 00:36:15,200 'Professor David Beerling's working life is devoted to the science of plants. 368 00:36:17,760 --> 00:36:22,160 'For him, the meeting of Calvin and Benson is pivotal 369 00:36:22,160 --> 00:36:25,120 'to the understanding of photosynthesis.' 370 00:36:26,160 --> 00:36:29,960 So what do we know about these two men? 371 00:36:29,960 --> 00:36:34,640 Benson was really following his own intuition and experimental programme 372 00:36:34,640 --> 00:36:39,120 and much of the work that he did Calvin was unaware of. 373 00:36:39,120 --> 00:36:44,600 Calvin had a lot going on and he was involved in running this lab and other research questions. 374 00:36:44,600 --> 00:36:48,880 He also had his own personal theory about how photosynthesis was working 375 00:36:48,880 --> 00:36:54,040 and he was very focused on addressing his own particular pet theory, 376 00:36:54,040 --> 00:36:59,040 and all the time you've got Benson looking on and seeing his boss pursuing 377 00:36:59,040 --> 00:37:02,680 what he knew to be, you know, a dead end. 378 00:37:02,680 --> 00:37:08,320 That's not a great basis for a working relationship. Rivals in the same team, no, not at all. 379 00:37:10,840 --> 00:37:14,320 To begin with, things are very different. 380 00:37:14,320 --> 00:37:17,400 Calvin and Benson work closely together, 381 00:37:17,400 --> 00:37:22,120 trying to figure out how plants use carbon dioxide to fuel their growth. 382 00:37:25,600 --> 00:37:29,680 Once again, botany benefits from a leap forward in science. 383 00:37:31,840 --> 00:37:37,760 Foremost among the new technologies of the age is a machine called a cyclotron. 384 00:37:37,760 --> 00:37:41,040 Invented at the Berkeley Radiation Laboratory, 385 00:37:41,040 --> 00:37:43,960 the cyclotron is a particle accelerator. 386 00:37:43,960 --> 00:37:48,240 It allows scientists to study the nucleus of the atom. 387 00:37:48,240 --> 00:37:50,560 CLICKING SOUNDS 388 00:37:50,560 --> 00:37:54,280 But that's not why it interests Benson. 389 00:37:54,280 --> 00:37:58,360 The cyclotron produces radioactive carbon atoms. 390 00:38:00,360 --> 00:38:02,600 'The Atomic Age. 391 00:38:02,600 --> 00:38:07,320 'Here is the answer to a dream as old as Man himself, 392 00:38:07,320 --> 00:38:11,280 'a giant of limitless power at Man's command. 393 00:38:11,280 --> 00:38:14,320 'And where was it science found that giant? 394 00:38:14,320 --> 00:38:16,320 'In the atom.' 395 00:38:18,440 --> 00:38:23,160 If the atom is radioactive, you can follow it wherever it goes. 396 00:38:27,600 --> 00:38:32,200 The idea is to replace the normal carbon atom in carbon dioxide 397 00:38:32,200 --> 00:38:34,640 with a radioactive carbon atom. 398 00:38:35,840 --> 00:38:40,760 By making the carbon dioxide radioactive before a plant takes it in, 399 00:38:40,760 --> 00:38:45,680 Benson believes he can track carbon's journey through the plant. 400 00:38:48,680 --> 00:38:54,000 If this works, Benson will have discovered how a plant uses carbon dioxide, 401 00:38:54,000 --> 00:38:57,040 something no-one else has done before. 402 00:38:57,040 --> 00:39:01,040 For a scientist, it doesn't get any more exciting than this. 403 00:39:16,440 --> 00:39:21,440 At the heart of the experiment is a glass disc shaped like a lollipop. 404 00:39:21,440 --> 00:39:27,320 It contains green algae growing in conditions that are perfect for photosynthesis. 405 00:39:30,320 --> 00:39:34,760 Inside his disc were algae busily photosynthesising away. 406 00:39:34,760 --> 00:39:38,520 When he introduced the radioactive carbon dioxide, 407 00:39:38,520 --> 00:39:41,120 the algae absorbed the gas. 408 00:39:41,120 --> 00:39:46,760 He then killed the algae and the chemical reactions stopped instantly. 409 00:39:48,040 --> 00:39:53,080 'By killing the algae with alcohol, Benson freezes a moment in time. 410 00:39:53,080 --> 00:40:00,440 'He then examines the dead algae to see how they've used the carbon in carbon dioxide to make sugars. 411 00:40:04,680 --> 00:40:09,760 'The radioactive compounds in the algae are separated on to sheets of paper. 412 00:40:10,880 --> 00:40:15,160 'These sheets are then pressed against X-ray sensitive film 413 00:40:15,160 --> 00:40:18,600 'to produce something called a chromatogram. 414 00:40:20,160 --> 00:40:24,680 'Each fuzzy blob here shows where the radioactive carbon has gone.' 415 00:40:26,800 --> 00:40:30,240 Why did a few smudges create so much excitement? 416 00:40:30,240 --> 00:40:32,840 This doesn't look very impressive, 417 00:40:32,840 --> 00:40:39,000 but this must have been their Eureka moment when they started getting these chromatograms. Really? Why? 418 00:40:39,000 --> 00:40:43,880 Because they realised that they could now see some of the key compounds 419 00:40:43,880 --> 00:40:50,440 that had used the radioactive carbon they'd fed the algae. So each blob is a different molecule? 420 00:40:50,440 --> 00:40:55,720 Each of these smudges represents a different chemical compound or a different sugar 421 00:40:55,720 --> 00:40:59,360 that represents a different stage in the pathway to carbon. 422 00:41:03,160 --> 00:41:06,760 'The pathway to carbon is effectively a road map, 423 00:41:06,760 --> 00:41:09,840 'showing how the plant makes sugar. 424 00:41:10,920 --> 00:41:15,360 'Understanding the first step on that road is crucial - 425 00:41:15,360 --> 00:41:19,440 'how a plant splits carbon from carbon dioxide. 426 00:41:19,440 --> 00:41:24,960 'Benson believes the answer lies with a protein that is common to all plants. 427 00:41:26,360 --> 00:41:32,680 'Calvin, on the other hand, has his own grand theory and isn't much interested in what Benson is up to. 428 00:41:36,160 --> 00:41:40,400 'So to begin with, Benson doesn't tell his boss what he's doing. 429 00:41:42,840 --> 00:41:47,680 'Calvin's theory of photosynthesis is eventually proved wrong. 430 00:41:50,320 --> 00:41:53,160 'Benson is the one who gets it right. 431 00:41:53,160 --> 00:41:57,640 'It's Benson who shows what happens during that first crucial step 432 00:41:57,640 --> 00:42:01,560 'when a plant grabs hold of the carbon in carbon dioxide.' 433 00:42:03,120 --> 00:42:07,760 Photosynthesis is often shown as carbon dioxide plus water and light 434 00:42:07,760 --> 00:42:10,720 equals sugar and oxygen. 435 00:42:10,720 --> 00:42:14,640 This seems to imply that that's a gross simplification. 436 00:42:14,640 --> 00:42:18,200 Yes, it's accurate, but it hides a huge amount of detail 437 00:42:18,200 --> 00:42:21,760 and a huge amount of elegance in the biochemistry. 438 00:42:21,760 --> 00:42:26,560 So it's not one big step, it's lots of tiny little hops? That's right. 439 00:42:26,560 --> 00:42:30,880 'Mother Nature doesn't give up her secrets that easily. 440 00:42:32,520 --> 00:42:35,280 'Every smudge has to be identified, 441 00:42:35,280 --> 00:42:40,080 'then they need to figure out how all the compounds work together. 442 00:42:40,080 --> 00:42:44,280 'It's a project that takes ten years to complete. 443 00:42:48,400 --> 00:42:52,200 'Benson receives no recognition for his work.' 444 00:42:56,840 --> 00:43:00,680 It's a familiar story. Someone makes a great discovery... 445 00:43:01,720 --> 00:43:04,240 And someone else takes the credit. 446 00:43:07,320 --> 00:43:11,360 In 1954, Benson is sacked from the university, 447 00:43:11,360 --> 00:43:14,720 leaving Calvin to work on without him. 448 00:43:19,840 --> 00:43:22,920 I want to show you another photo. 449 00:43:22,920 --> 00:43:27,440 It's 1961 and Melvin Calvin is receiving his Nobel Prize 450 00:43:27,440 --> 00:43:31,120 for cracking the role of carbon in photosynthesis, 451 00:43:31,120 --> 00:43:34,280 but there's something or someone missing. 452 00:43:36,760 --> 00:43:39,760 Andrew Benson is nowhere to be seen. 453 00:43:44,160 --> 00:43:48,480 To begin with, both men are credited for their work on photosynthesis. 454 00:43:51,720 --> 00:43:55,200 Now only one name takes centre stage. 455 00:44:01,480 --> 00:44:06,760 The passing of the years did little to soften Calvin's approach to his colleague. 456 00:44:08,840 --> 00:44:13,360 This is Melvin Calvin's autobiography and it tells a story 457 00:44:13,360 --> 00:44:18,160 of how he and his team unlocked the secrets of photosynthesis. 458 00:44:18,160 --> 00:44:22,600 It was published 30 years after he was awarded the Nobel Prize 459 00:44:22,600 --> 00:44:25,720 and in all 175 pages, 460 00:44:25,720 --> 00:44:29,520 there is no mention of Andrew Benson. Not once. 461 00:44:29,520 --> 00:44:32,200 It's as though he never existed. 462 00:44:38,280 --> 00:44:43,520 'Carbon's journey from gas to sugar became known as "the Calvin cycle". 463 00:44:45,600 --> 00:44:49,960 'Today, many botanists recognise Benson's contribution 464 00:44:49,960 --> 00:44:53,080 'and call it "the Calvin-Benson cycle". 465 00:44:58,880 --> 00:45:04,840 'Benson may have missed out on the Nobel Prize, but his contribution hasn't been forgotten.' 466 00:45:04,840 --> 00:45:07,880 So how important is Benson's work? 467 00:45:07,880 --> 00:45:13,200 Andy Benson's discoveries were absolutely amazing. 468 00:45:13,200 --> 00:45:18,520 They filled a huge gap in our knowledge about how plants photosynthesise 469 00:45:18,520 --> 00:45:22,600 and in a sense the discovery of that pathway of how they do that 470 00:45:22,600 --> 00:45:26,560 is comparable to Watson and Crick figuring out the structure of DNA. 471 00:45:30,160 --> 00:45:33,600 Today, we not only know how plants grow, 472 00:45:33,600 --> 00:45:38,680 but with the latest technology, we can watch them grow, cell by cell. 473 00:45:40,720 --> 00:45:45,760 The tip of this root is forcing its way through the earth. 474 00:45:45,760 --> 00:45:50,520 By taking carbon dioxide and converting it into sugars and starch, 475 00:45:50,520 --> 00:45:54,080 the plant has the energy it needs to grow. 476 00:46:06,200 --> 00:46:11,560 It may seem like we now know everything there is to know about photosynthesis... 477 00:46:12,680 --> 00:46:15,080 ..but that's not the case. 478 00:46:16,360 --> 00:46:22,240 For instance, the environment in which plants grow can vary dramatically and yet they survive. 479 00:46:26,280 --> 00:46:29,120 Plants are very sophisticated. 480 00:46:29,120 --> 00:46:35,640 From the Equator to the Arctic Circle, they photosynthesise in all sorts of conditions. 481 00:46:35,640 --> 00:46:39,960 And they have to respond to their environment in order to grow. 482 00:46:39,960 --> 00:46:44,400 And even here in Britain, plants have a lot to contend with. 483 00:46:50,200 --> 00:46:52,880 Whether they live high on a hill top 484 00:46:52,880 --> 00:46:55,600 or down on the valley floor, 485 00:46:55,600 --> 00:46:58,960 plants have adapted to where they live. 486 00:46:58,960 --> 00:47:01,600 Take this ivy, for example. 487 00:47:01,600 --> 00:47:05,640 It's growing on a north-facing cliff so it gets no direct sunshine. 488 00:47:05,640 --> 00:47:09,760 Furthermore, it's got trees forming a canopy over the top of it. 489 00:47:09,760 --> 00:47:16,040 It's got no real soil to get its roots into, so it has no permanent supply of water 490 00:47:16,040 --> 00:47:21,400 and yet there's lots of it. It is brilliantly adapted to these growing conditions. 491 00:47:28,120 --> 00:47:31,960 Whether it's poor light or not enough soil, 492 00:47:31,960 --> 00:47:35,840 plants have to make the most of their surroundings. 493 00:47:35,840 --> 00:47:39,560 That's because, unlike me, they're rooted to the spot. 494 00:47:40,640 --> 00:47:44,440 They can't go searching for water if they're thirsty 495 00:47:44,440 --> 00:47:47,360 or find a shady spot to hide from the sun. 496 00:47:48,520 --> 00:47:53,400 Up on the top of the hill, there's plenty of light. That's not a problem. 497 00:47:53,400 --> 00:47:56,440 Here, it's the wind drying out the plants 498 00:47:56,440 --> 00:48:00,280 that makes water the limiting factor for photosynthesis. 499 00:48:06,320 --> 00:48:09,160 Plants either adapt or die, 500 00:48:09,160 --> 00:48:12,920 so they've come up with clever ways to survive. 501 00:48:14,000 --> 00:48:18,760 And we've developed methods to turn this ability to our advantage. 502 00:48:19,920 --> 00:48:26,560 Farmers have learned how to make the most of photosynthesis in all sorts of conditions 503 00:48:26,560 --> 00:48:32,720 and in modern glasshouses, they can manipulate the environment to increase production, 504 00:48:32,720 --> 00:48:36,200 often in ways that are quite surprising. 505 00:48:38,200 --> 00:48:40,520 SHEEP BLEATING 506 00:48:42,280 --> 00:48:46,880 The Netherlands is one of the world's smallest countries, 507 00:48:46,880 --> 00:48:50,840 yet it has become one of the world's biggest food exporters. 508 00:48:53,920 --> 00:48:56,440 In these vast greenhouses, 509 00:48:56,440 --> 00:49:01,920 commercial growers have learned to manipulate the building blocks of photosynthesis. 510 00:49:04,160 --> 00:49:07,640 They don't rely on sunlight to grow crops. 511 00:49:09,960 --> 00:49:14,000 They can make their own with the help of 3,500 light bulbs. 512 00:49:17,360 --> 00:49:23,160 When the sun goes down, the lights come on and the plants continue to grow. 513 00:49:25,080 --> 00:49:27,560 By changing the lighting conditions, 514 00:49:27,560 --> 00:49:33,120 they can bring forward the growing season of these peppers by four weeks. 515 00:49:34,600 --> 00:49:39,320 More light buys the plant more time to turn sugar into fruit. 516 00:49:44,320 --> 00:49:50,800 With sunlight guaranteed, this greenhouse produces 14 million peppers every year. 517 00:49:53,960 --> 00:49:59,960 Sunlight isn't the only part of photosynthesis that can be manipulated to our advantage. 518 00:49:59,960 --> 00:50:02,240 Thanks to a quirk of evolution, 519 00:50:02,240 --> 00:50:07,640 changing the levels of carbon dioxide can also have a dramatic effect. 520 00:50:07,640 --> 00:50:11,840 There have been times in the history of the Earth 521 00:50:11,840 --> 00:50:15,880 when the carbon dioxide levels were very different 522 00:50:15,880 --> 00:50:22,360 and as a result, plants have the capacity to use extra carbon dioxide to make more sugar 523 00:50:22,360 --> 00:50:24,440 and to produce bigger fruit. 524 00:50:30,080 --> 00:50:35,960 Commercial growers have been quick to exploit this legacy of our planet's past. 525 00:50:38,120 --> 00:50:44,080 Today, this Suffolk greenhouse produces 50% of all the tomatoes grown in Britain. 526 00:50:47,200 --> 00:50:51,160 The secret to more tomatoes is more carbon dioxide. 527 00:50:55,280 --> 00:50:59,040 Next door to the greenhouse is this factory. 528 00:50:59,040 --> 00:51:01,480 It generates two waste products. 529 00:51:01,480 --> 00:51:05,360 One is steam which escapes up these chimneys 530 00:51:05,360 --> 00:51:08,280 and the other is carbon dioxide, 531 00:51:08,280 --> 00:51:12,720 a greenhouse gas that you don't want to release into the atmosphere. 532 00:51:14,680 --> 00:51:20,840 So instead, this greenhouse gas gets pumped from the factory into...a greenhouse. 533 00:51:23,080 --> 00:51:26,360 These plastic tubes have tiny holes 534 00:51:26,360 --> 00:51:30,640 which deliver the gas to the leaves of the tomato plants. 535 00:51:35,040 --> 00:51:39,720 Give a tomato plant extra carbon dioxide and it produces more sugar 536 00:51:39,720 --> 00:51:44,000 which makes for a sweeter tomato which is good for us. 537 00:51:44,000 --> 00:51:46,280 It also doubles the yield 538 00:51:46,280 --> 00:51:49,160 which is good for the grower. 539 00:51:50,320 --> 00:51:53,720 By fine-tuning the environment of plants, 540 00:51:53,720 --> 00:51:55,800 we can grow more food. 541 00:51:59,320 --> 00:52:04,880 These commercial growers have got photosynthesis down to a fine art. 542 00:52:04,880 --> 00:52:08,680 They can manipulate it, but that's as far as it goes. 543 00:52:08,680 --> 00:52:12,040 Plants are still doing all the hard work. 544 00:52:19,080 --> 00:52:25,640 Turning water and carbon dioxide into leaves, seeds and fruits makes huge demands on a plant. 545 00:52:27,360 --> 00:52:31,360 To fuel this growth, it needs a reliable source of power. 546 00:52:32,480 --> 00:52:36,440 However different they are, wherever they come from, 547 00:52:36,440 --> 00:52:43,040 plants are all able to survive and grow because of their ability to harness energy from the sun. 548 00:52:49,560 --> 00:52:54,360 The amount of light energy converted by photosynthesis is staggering. 549 00:52:57,160 --> 00:53:01,640 In one year, all the plants on Earth generate enough energy 550 00:53:01,640 --> 00:53:04,640 to power human civilisation six times over. 551 00:53:06,720 --> 00:53:10,960 We now know a great deal about photosynthesis. 552 00:53:10,960 --> 00:53:15,360 We can manipulate it to make better crops and feed more people. 553 00:53:15,360 --> 00:53:20,040 But this is just the start. The next step is really exciting. 554 00:53:20,040 --> 00:53:27,120 And if science gets it right, it will alter lives for generations to come. 555 00:53:39,760 --> 00:53:43,880 At the University of Glasgow, Professor Lee Cronin is trying 556 00:53:43,880 --> 00:53:48,160 to recreate photosynthesis in his laboratory. 557 00:53:48,160 --> 00:53:53,440 Something that plants have been doing for more than a thousand million years, 558 00:53:53,440 --> 00:53:56,680 he is trying to do artificially in a decade. 559 00:53:59,640 --> 00:54:04,200 Plants use the sun's energy to split water into hydrogen and oxygen, 560 00:54:04,200 --> 00:54:08,320 two gases that could help make the fuels of the future. 561 00:54:09,800 --> 00:54:13,920 It's this process that Lee is trying to copy. 562 00:54:15,920 --> 00:54:19,920 This very thin electrode where you see all these very small bubbles 563 00:54:19,920 --> 00:54:23,520 is a platinum electrode where the hydrogen is coming off, 564 00:54:23,520 --> 00:54:29,160 and at this black electrode with the slightly bigger bubble is where the oxygen is being produced. 565 00:54:29,160 --> 00:54:35,080 This normally happens inside a leaf, but here it's happening in this flask. Exactly. 566 00:54:35,080 --> 00:54:37,440 'There's still a long way to go. 567 00:54:38,520 --> 00:54:41,720 'Lee can't split water using just light. 568 00:54:41,720 --> 00:54:43,760 'Not yet anyway. 569 00:54:43,760 --> 00:54:47,040 'He still needs a battery to power the process, 570 00:54:47,040 --> 00:54:49,560 'but the potential is enormous.' 571 00:54:49,560 --> 00:54:56,120 If we let this go long enough, the water in here would get less and less as it's being converted to the gas 572 00:54:56,120 --> 00:55:00,200 and there'd be nothing left at the end. How long would that take? 573 00:55:00,200 --> 00:55:06,200 Probably... Well, at this rate, probably a few days. Right. So we don't need very much water. 574 00:55:06,200 --> 00:55:09,280 There's a huge amount of gas locked up in here. 575 00:55:09,280 --> 00:55:15,040 But this is the critical first step of the photosynthesis story? Yeah, exactly. 576 00:55:15,040 --> 00:55:18,560 Once we've perfected the first step, there is a critical part 577 00:55:18,560 --> 00:55:24,400 where we take carbon dioxide from the atmosphere and complete the story and turn the carbon dioxide 578 00:55:24,400 --> 00:55:28,000 into a fuel that we could put in an aeroplane or a car. 579 00:55:28,000 --> 00:55:34,680 So our family cars could start, in years to come, from a process like this with water being split? 580 00:55:34,680 --> 00:55:38,640 There's every possibility. We're very excited about it. Wow! 581 00:55:38,640 --> 00:55:43,160 'So he should be. The prize is clean and limitless energy. 582 00:55:43,160 --> 00:55:48,800 'No wonder labs like this all over the world are working hard to crack the problem.' 583 00:55:48,800 --> 00:55:55,320 If we get this right, if we're able to understand and learn from photosynthesis in such a way 584 00:55:55,320 --> 00:56:00,200 that we can surpass evolution if you like and make an even better device 585 00:56:00,200 --> 00:56:05,520 to take light energy, carbon dioxide and water and produce a fuel, 586 00:56:05,520 --> 00:56:10,920 then this is going to have massive ramifications for our society and our environment. 587 00:56:24,880 --> 00:56:27,400 Lee's work is impressive, 588 00:56:27,400 --> 00:56:31,280 but it shows how sophisticated photosynthesis is 589 00:56:31,280 --> 00:56:34,760 and scientists will be hard pressed to replicate it. 590 00:56:34,760 --> 00:56:38,800 The thought that it may provide an alternative source of energy 591 00:56:38,800 --> 00:56:42,120 confirms the awesome power of photosynthesis. 592 00:56:44,880 --> 00:56:50,760 To see the power of photosynthesis in action, take a look at these images from NASA. 593 00:56:50,760 --> 00:56:55,040 They show how photosynthesis varies across the globe 594 00:56:55,040 --> 00:56:58,160 with the ebb and flow of the seasons. 595 00:56:58,160 --> 00:57:00,640 That's not the whole story. 596 00:57:00,640 --> 00:57:03,440 What's fascinating is the oceans. 597 00:57:04,760 --> 00:57:07,480 They're glowing green. 598 00:57:07,480 --> 00:57:14,040 That's because half of the world's photosynthesis takes place not on the land, but in the sea. 599 00:57:16,520 --> 00:57:21,480 How close are we to understanding all there is to know about photosynthesis? 600 00:57:21,480 --> 00:57:28,080 We understand the broad principles of how photosynthesis works, but the real fine detail still eludes us. 601 00:57:28,080 --> 00:57:33,000 We can put a man on the moon, but we can't mimic photosynthesis. 602 00:57:40,600 --> 00:57:46,200 Botany has come a long way since the time when people believed plants eat soil. 603 00:57:48,160 --> 00:57:51,720 Today, we can feed more of the world's population. 604 00:57:51,720 --> 00:57:56,080 Tomorrow, we may even find a way to fuel our planet. 605 00:57:58,120 --> 00:58:00,640 And it's all down to photosynthesis, 606 00:58:00,640 --> 00:58:05,240 for me, the most remarkable and important process on Earth. 607 00:58:06,800 --> 00:58:09,680 Next time on Botany: A Blooming History... 608 00:58:10,840 --> 00:58:16,400 I'll be looking at how botanists puzzled over the colours of snapdragons, 609 00:58:16,400 --> 00:58:20,240 investigated the mysteries of wild maize 610 00:58:20,240 --> 00:58:24,600 and developed a brand-new science - plant genetics. 611 00:58:45,920 --> 00:58:49,920 Subtitles by Subtext for Red Bee Media Ltd 2011 612 00:58:49,920 --> 00:58:52,920 Email subtitling@bbc.co.uk