Melvyn Bragg and his guests discuss photosynthesis, the process by which green plants and many other organisms use sunlight to synthesise organic molecules. Photosynthesis arose very early in evolutionary history and has been a crucial driver of life on Earth. In addition to providing most of the food consumed by organisms on the planet, it is also responsible for maintaining atmospheric oxygen levels, and is thus almost certainly the most important chemical process ever discovered.
Nick Lane
Reader in Evolutionary Biochemistry at University College London
Sandra Knapp
Botanist at the Natural History Museum
John Allen
Professor of Biochemistry at Queen Mary, University of London.
Producer: Thomas Morris.
United States


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00:00:17I hope you enjoy the program hello three and a half billion years ago this planet as a whole style and barren place the atmosphere was toxic and contained no oxygen and life on earth was restricted to a variety of unsophisticated single celled or single celled organisms which lived
00:00:34in the city but then in Utah the organism emerge one with an amazing new capabilities could harvest energy from sunlight and use it to fuel its own activities this phenomenon is known as photosynthesis and is almost certainly the most important chemical process on us plants and some other
00:00:51organisms depend on it for the energy on almost all life is ultimately reliant on it for survival is responsible for the food we eat in the air we breathe and without it earth would still be Stara rather than as it is teeming with life with me to discuss
00:01:05the distances on Sunday not a botanist at the natural history museum neckline read an even richer biochemistry at University College London and Joan Allen professor of biochemistry at Queen Mary university of London sound enough would you give us some idea of what to senses is and why it's
00:01:24so important photosynthesis is one of those things that you always read about you hear about at school but actually when you look at it carefully what it is is it's a very simple elegant chemical reaction which involves an organism taking water and carbon dioxide and with the help
00:01:40of light turning those into glucose and oxygen so it's it's water and parts of the air turned into sugar and a really important part of the air for us and the reason it's so important is because without photosynthesis that blue and green bowl that you see from space
00:01:57would look like Mars and can you just developed a bit of of the importance of it and how it changed things well when when organisms were able to create their own food to create their own it to create something from light that then allowed other organisms to feed
00:02:15on them so you have water trucks which are organisms that make their own food so plants are also trust anything that does photosynthesis is an artichoke we are completely hopeless where heterotrophs we depend on other organisms for our food so without without these photosynthetic organisms we would have
00:02:32nothing to eat nothing to breed and so all of life really depends upon autotrophs it's also true I think that we look at at photosynthesis it seems that's the sort of simple end but you look at the structural diversity of life on earth sort of that we have
00:02:46rain forests and we have desert some we have all these different types of habitats depends upon the different types of older trucks which are in those habitats which then drive the development of communities that are in all the different biomes honor what are the basic rule materials for
00:03:00photosynthesis what is a plant for instance need anyone to photosynthesize well it first of all it needs water needs carbon dioxide there needs to be light and also need to be a few really important mineral these trees are most likely a light is the most important I thought
00:03:18would think water water is also very important in carbon dioxide can be in varying concentrations and that makes a big difference and I'm sure my bio chemical colleagues will be able to tell us about that but but it also needs sort of a few other things as well
00:03:30up plants need nitrogen phosphorus to make the enzymes which drive the reactions of photosynthesis and I also need an element a mineral called magnesium which six like a spider at the center of the chlorophyll molecule which is what what one of the light harvesting pigments in in leaves
00:03:45so we don't know what the distance is part of a central part of a little barbiturates business engines yes an engine room is an engine room is essentially is essentially plant power is what it is the plan if we think about let's stick to a plan so that
00:04:00sick plans from time what are the structures in the plan so that make that since as possible you don't have to rush we'd all like to know in detail okay well it all goes on inside a special compartment inside the cell which is called Clark last the chloroplasts
00:04:18in front of what once bacteria in their own right they were free living bacteria we think we know them a sign about Terry and now I'm Dave became captured probably something in the order of one billion to one and a half billion years ago %HESITATION final complex cells
00:04:34in advance and they they became responsible for photosynthesis they continue to do what they were doing before you say became captured the that sounds terrific but let me don't know what you mean while they were simply a engulfed by a larger sal and effectively put to work not
00:04:50quite as slaves but they did what they always did say they continue to photosynthesize they continue to take electrons from water put them onto carbon dioxide and make sure because that way and so the host cell which had captured them games those benefits of of of of getting
00:05:08a free lunch you might say is the the throw away energy I said to send me a few moments ago he's the I'd really be an engine does not make any sense that useful for people to the I think absolutely isn't some engine Sir can you tell us
00:05:22what's happening inside this enjoyment just tell us to get well we have a series of membranes a call to find a chord membranes I'm is an enormous complexes of proteins I mean this is one of the difficult things to try to get across because I say enormous complexes
00:05:39but this is all microscopic of course but if you take yourself down to the size of a small molecule say this side of an oxygen molecule these complexes is like being in in some kind of huge industrial complex %HESITATION so they're really enormous and they sit there in
00:05:55in the membranes all they do at the chemical level is really amazingly simple all they do is they extract electrons from water and they pass them down a kind of a chain and eventually they push them onto carbon dioxide to make sure this now it sounds heavy chemical
00:06:13level is very simple at the biochemical level it's enormously difficult these complexes well it is not easy to get electrons out of water in the first place so you know it the largest storms crashing water against a secret is not going to break water down into into its
00:06:29component parts but light can do that now likes doesn't normally do that certain wavelengths of UV light can split water but but by and large it requires the bio chemical skill which which we can mimic but with great difficulty actually implants just simply do it they simply extract
00:06:49these these letters only pass them down and they they push them on to CO two the missive involved to do it over a long period of time we don't know what they what do they want to do why do they want to do it that's always a difficult
00:07:02question in the evolution %HESITATION essentially water is everywhere if you can crack that %HESITATION than than you've you've you've got your raw material that you need in the oceans surrounding you the other materials that could be used things like hydrogen sulfide gas which is just a dissolved by
00:07:20and for example if you have no option around you can you can use I am but they they're far less common water is the perfect fuel via the process as I read from my notes on making a lot of tension on its on this program can be separated
00:07:34into two separate chemical reactions can you tell us what those two are well very %HESITATION then known as the light in the dark reactions and really it's it's acted simplest the light reaction is is driven by the absorption of photons of of light %HESITATION I'm Anne simply dragging
00:07:53stripping electrons from from water so that's essentially what what's being powered by the light reaction is the removal of electrons in water the waste of this his oxygen which is just you know it's a waste product of photosynthesis it's just let go is not even that was fair
00:08:09auctions always but it's always buy products yes so then the dog action you take those electrons you force them on to combat was I know that doesn't require light a tool so it's called it used to be called the dark reaction %HESITATION they they they changed the name
00:08:25recently to me nonwhite reactions I think but I prefer the old term that that the dog action it can happen in the dark it gets more and more mysterious and the simple you make at the moment sure should also gets Joan Allen at the heart of this process
00:08:39is this molecule called chlorophyll now what so specific about that what's so special about the well %HESITATION interesting to follow Nick you know oxygen is not just a waste product said toxic waste product we don't think of is toxic we may come back to that merciless one night
00:09:00counties like that I mean why is it well well two point four five million years ago as you said in the introduction the whole biosphere was working fine without free molecular oxygen this was dangerous stuff to have arrived is chemically highly reactive two point four seven million equals
00:09:22billion he is ago this trick was discovered by accident of taking electrons from water producing this by product this was a big shock to the system there's never been an equivalent environmental catastrophe full life that existed before that as it is as the production of all the production
00:09:42of offering a poison gas actually which nevertheless doing that trick had such immense value again discovered by accident it wasn't because I wanted to do this I know that you were speaking metaphorically that %HESITATION issues has such benefit that they had to learn to live with these poison
00:09:59gas and learning to live with this guy lose that they were the openness everyone pretty well everything that I had to deal with oxygen as it came along they're still environments today whether we're oxygen doesn't permeate and there is still anoxic life without oxygen was a relic of
00:10:15this full time which is done in the club to the other yeah under the in the in the rocks and the listeners feel and be back at Laura film I wasn't evading the question under you and I understand that I just got interested by doctors should be good
00:10:30toxic waste it's like reading an entirely different experience look to us for such things chlorophyll well it it's this is one of the phone was the time honored tradition of giving things Greek names it simply means Greenleaf Perot fill it's some it's a chemical substance it's an organic
00:10:49chemical substance %HESITATION the structure which I can describe very briefly if you sandy was right about this magnesium item in the middle of a spider's web the spider's web is some build up of essentially for Calvin items if you imagine them being linked to series one two three
00:11:11four and then you add a fifth Clinton which is not common but nitrogen a new full letter room to make a circle five membered objection Pentagon actually that some that is %HESITATION at a simple %HESITATION circular molecule which is the one of the building blocks another four of
00:11:34these %HESITATION is cool pie role is a technical term there four of these in the basic head group of chlorophyll and these one two three four also arranged in a in a series and you feel that around to make a circle under the center of that within ninety
00:11:52nine gin items pointing in which is the magnesium at him naturally chlorophyll except you just have to add the fact that there's a a hundred Cup and tail attached to one of these rings which gives chlorophyll the property of being completely insoluble in water but soluble in organic
00:12:11solvents and also is preferred location is within biological membranes which of fatty waxy or oily %HESITATION components this is what's so special and essential about it as well %HESITATION especially the sensual %HESITATION I mean the first thing there really is there's nothing magical about it %HESITATION you know
00:12:33in the history of saw in biology people of always wanted to be focusing down on what's the smallest thing that we can save a life when people thought got very excited about chlorophyll it seems to be a very special moment in sustaining life on this but in fact
00:12:48it's it's just a chemical in fact it's been synthesized in buying a synthetic organic chemists in Harvard University in the sixties or seventies from scratch you can make the whole thing to the full civil kind of chemistry plants do this via my chemical possibly I'm told that there
00:13:05are two separate sets of chlorophyll involving the structures all right yes that's what they do how do they do well that's correct %HESITATION they do essentially the same thing Nick talked about this chain of electron care is and the great insight was provided in nineteen sixty in fact
00:13:29by hill and depend on the paper published in April nineteen sixty they said in this first of all there is a chain of electoral carriers secondly there are two points in that chain of electron carriers when the electrons wouldn't go unless they were given a push by some
00:13:48energy energy input and not push it provided by light energy acting on chlorophyll one of the fates of the energy when the chlorophyll molecule has absorbed light is for it to lose an electron that match the beginning that's the whole **** drives this electron transport chain that special
00:14:10chlorophyll loses its electoral to stone the chain is just one of three hundred chlorophyll molecules approximately the only others take the absorbed excitation energy and pass it amongst each other until it arrives at the special one in that sense the whole process going and sustains life on earth
00:14:29as we hood before the sun and we've been talking about for the sins is as if you were single process but there's more to those that has more than one type can you tell us about that sure that that photosynthesis is their most plants are what's called see
00:14:46three photosynthesize ours and it's called see three because the first thing that happens to the carbon dioxide when it gets split up as it turns into a three carbon molecule but there's a whole set of flowering plants and it happens all over which are called see for plants
00:15:00and what they do what they do is the is the first reaction is slightly different in the carbon goes into a for the comedy acts like it's broken up into a a for carbon molecule and then the photosynthesis happens in two different places to different types of cells
00:15:13normally just happens in one part of one part of the cell but in in in C. for photosynthetic plans what happens is this the CO two is sort of stored it sort of packaged into special they're called bundle sheath cells and there around the vasculature so they're around
00:15:28the veins you think about a leaf it has it has a set of veins and that's where the water is is running up and that sugars are running down and these these special bundle sheath cells where this carbon dioxide is stored and see for plants are much more
00:15:42efficient at photosynthesis at high temperatures so often times things that growing desert in a very hot places RC four put a synthesizers and there's a third kind which is called cross delays in acid metabolism so Cham Cham plants in it it come because it was first it was
00:15:57first time discovered in a in a seat him in one of those little rock plants the ground rock gardens which are in the family crest you Lacy and so it's called crossing a scene acid metabolism in those plans what happens is the stone makes which is where the
00:16:10stories are like little holes in a leaf so he take a hand lens and look at the bottom of a leaf very carefully you see tiny little pets and those little pets are our pores in the leaf which it would have to guard cells around them almost like
00:16:23almost like a mouth that can open and close and that CO two goes in through these pores so question is an acid metabolism plans on keep their still mates close during the day all the plants open their stomachs during the day so this can all go on in
00:16:38the light crystallize in acid metabolism plants keep those clothes during the day and open them at night when it's not so hot they do all the business of taking in the CO two at night and then store it and so can plants can idle so they can they
00:16:53can store up all the all the components for photosynthesis and kind of do it later which is really useful if you live in a desert so many cam plants are things like cacti in orchids and the kinds of plants that live in very hot dry stressful environments but
00:17:08if you do it in the dark with the new polite they think they stay harvest the light as well so it all gets it all gets me today yes but you said that because of the no left dominates the stomachs of the light comes in through that through
00:17:21through the cells of the plant light doesn't come in the store mates are what take in the gas and so see four plants are very interesting because if you look at the distribution of C. foreign three three plants across Florida and many of our major crops corn maze
00:17:36for example is a C. for plant in this is been studied the most in the grasses and the sea for plants are highly partisan vertically fashion and so one of the great holy grails in agriculture is to take a C. three plant like rice or wheat and turn
00:17:50it into a sea for plant which would increase its efficiency and thereby perhaps increase its yield and its its ability to grow in different parts of the world okay niggling what does the plant so do with the energy that it Sam conventicle explain that again or not yes
00:18:07well in that I I you talked earlier about there the flow of electrons now they they do two things %HESITATION you have essentially a current of electrons and that is used to drive %HESITATION protons so the the the %HESITATION positive %HESITATION nucleus of hydrogen atoms across the membrane
00:18:28so you end up with a proton gradient across the membrane now that's common to all said I just want to be a slow well yes essentially on one side of the membrane you have a large number of protons on the other side you have very few relatively few
00:18:41so it's essentially like a hydroelectric power scheme with the reservoir on one side and a turbine in the membrane itself so the turbine is a is an enzyme called the ATP synthase enzyme and that is powered by the flow of protons as as from from the reservoir back
00:19:01to the side where this is down hill in effect I'm I'm not produces a TP now ATP is generally called the energy currency of life is it's %HESITATION this used by all living cells I invite the ATP synthase as well which produces it is also used by almost
00:19:18all the living cells I'm I'm not powers everything in the cell you could think of it like a a small coin in the slot machine basically all proteins to do any work told a change that confirmation and change their shape requires splitting an eighteen page so the current
00:19:35of electrons which is flowing from water to CO two is driving all of this process the second thing that happens is they all those electrons end up on combat outside converting it into a sugar and those sugars are then into converted into all the rest in an old
00:19:51trophy up plants and so on converted into all the rest of the organic molecules that we need to feel that they need to live that we need to aids so %HESITATION growth basically is both power and growth of coming from photosynthesis in your minds again because this is
00:20:07more and more industrialism advocate your mind is again the size of these things the size on which they're operating yet anyone is feeling is going to say it's it's kind of difficult to grasp the chloroplast itself is the size of a bacterium he was about to him so
00:20:23you can't really see it except down the microscope down a microscope you come see them down a light microscope you can see them quite well so you you could if you have a you know a reasonable microscope home you could see them but they're in the order of
00:20:37%HESITATION you know a fraction of a millimeter something like a tenth of a millimeter also in in in there like this is the car plus this is the engine house where all this is happening I'm beyond that within the chloroplast itself you have these big proteins within the
00:20:55membranes themselves now these are what I was calling the industrial complexes before and if you string to self down to the size of a molecule like oxygen %HESITATION then then really it's it's it's like a city now there are tens of thousands of these great industrial complexes within
00:21:12a single car plus is very difficult to it too to grasp this scale that something so small it impacted practically a city in itself ended up I was just gonna say that the Tom if you buy Spiro gyro which is one of these health food things from the
00:21:26health food store and then waited up and look at it with the with the with the lens you they have pretty big chloroplasts and you can see them and they're like little green little greens long things are really rather beautiful color plus your knowledge of virgins issues yes
00:21:42warn of the chemical processes in the plant another's respiration can you tell us how these relate to each other that well it's that's a good question you know I'm sandy's definition photosynthesis %HESITATION is release of oxygen uptake of carbon dioxide this is good Mrs correct this is what
00:22:03plans do that that that that there is another view which may come to an end and if you take that view Arabic respiration which is respiration plants do and which we do we're all doing it and I wish the up tank of oxygen %HESITATION input electrons onto it
00:22:24to make water source the reverse of taking electoral from wanted liberale shin we take up all she had to take a deep deep deep breaths here and we respond to make ATP by exactly the process that Nick just described %HESITATION any not process we released Kudlow sites of
00:22:41photosynthesis is release of oxygen uptake of **** looks like respiration is uptake of oxygen really succumb books which we're all doing no I don't hate for truth we will federal troops sitting right here responding and getting our energy from ultimately from sunlight %HESITATION what a story by photosynthesis
00:23:05so percentage point of view restoration photosynthesis of the reverse of each other I just think it was a token for the position totally correct botanical description however if you look more deeply at the at the kind of level that Nick is describing the process of energy transduction we
00:23:26could say power station is a good analogy could be made evil power station like a water mental something with converting energy from one form into a different form the way in which that done it is done is universal in biology and photosynthesis and respiration two ways of applying
00:23:47the same fundamental mechanism electron transport moving protons across the membrane to make a gradient which is stored energy and used to make ATP so in that sense that the same process except the chlorophyll in the photosynthetic reactions and to give the electronic initial portion needs in respiration if
00:24:11the electrons just sort of flow where they want to go neckline yeah the one that does the source of electrons is really is really the the major difference between photosynthesis and respiration so in restoration we need an easy source of electrons that food in our own case and
00:24:29the food will reacts spontaneously with oxygen it doesn't happen right now because there are barriers to it happening but but in terms of the thermodynamics they want to react with each other and it will happen and the enzymes in the mitochondria allow that to happen what's happening photosynthesis
00:24:47is that life is is providing that essential input of energy which flows which which which would start electrons flowing from far more difficult places so water in this case so water really does not want to lose its electrons but the input of like through chlorophyll extract selections from
00:25:04it and sets them flowing in exactly the same way that they flow from food to auction in us that it is exactly the same processes that the source of electrons differs I'm still reading fall this thing that's a tenth of a of the smallest thing I can properly
00:25:20thing called how cities inside it on we go I'm sending up the the punch and back here live in a wide variety of habitats within the limiting factors on other anyone factor weather info to synthesisers efficiency there certainly limiting factors if you there's no water in the environment
00:25:37plants got photos of this nothing can photosynthesize because water is one of those inputs same is true for carbon dioxide same is also true for light but they're all they're also limits and things like nitrogen and phosphorus those which is part of the reason that we fertilize crops
00:25:51is to is to increase photosynthetic efficiency and thereby increase yield that you need the nitrogen in the phosphorus to build the other enzymes that that operate in this little factory but but of temperature is a very important limiting factor for photosynthesis as well at very high temperatures photosynthesis
00:26:08doesn't happen particularly efficiently and a very low temperatures so there's an optimum range and one of the things that's really interesting about plants is that people often think of plants is just sitting there right plants just sit there and kind of death plants behave is just on a
00:26:22very different scale to our human behavior and so if there's if there's not enough water or if there's too much light on the still meets were close and at the end and thereby no carbon dioxide is taken in and photosynthesis go down so plants regulate the degree to
00:26:39which they photosynthesize dependent on various environmental conditions the most important of which are probably water and carbon dioxide concentration which is interesting in the context of climate change is interesting in the context of of the different carbon dioxide concentrations over the history of life on earth and your
00:26:55own audience chlorophyll isn't in the pigment that's the pigment that gives a screen Instagram a powerful all the others as important yeah well there are others that serve to collect the life energy and to them ultimately deliver it to this special chlorophyll let lose its electoral which stops
00:27:15the whole process of their own carotenoids %HESITATION these don't engage in this chemical reaction but they absorb light on the energy is transferred %HESITATION into this sort of in bowl game of of chlorophyll molecules when it finally ends up in one special one %HESITATION there of the %HESITATION
00:27:40pigment molecules to the cyanobacteria for example and red algae which a witch on a room %HESITATION eukaryotic which of plants of these have %HESITATION pigments which absorb light energy which is used for photosynthesis again essentially by chlorophyll these pigments ana I mentioned the full rings these are linear
00:28:03check for Pareles rather than cyclic touch apparels I'm so there's a whole range of different pigments that different photosynthetic organisms of sort of latched onto an exploitative if if they're useful for capturing on concentrating light energy wise chlorophyll green that's such a good question and you know I
00:28:24have to confess I don't know the answer lots of people have asked that question why is it clean underwent the rushing and it's not green we see it as green because green is the only thing that isn't absorbed green is the only way like that isn't up some
00:28:37some nothing really has color we just perceive it because the what of the wavelength of light which is reflected off it so so it it's interesting there's a there's a concept called Claire affiliate which is about the love of the love of green things which I think is
00:28:52a nice a nice thing to be I think John once a little well known here okay what one is chlorophyll green because it absorbs blue light and red light and doesn't absorb light in the middle of the valley visible spectrum which is green I mean that's true but
00:29:10that's just some stating something an argument here I mean Elvis mill this question if I may could be re phrase white owned plants black right if they were black they would be absorbing all this we could start again no no way they green I mean why are they
00:29:27not making use of green light them they should really if they were interested in getting the most energy they would use the whole of the visible spectrum and would be black and then all but just so so much a question still let's make of you've got the answer
00:29:40no but I have a small contribution I mean it's interesting that they use red lights mostly Soviet they they that the spectrum of light that powerful is absorbing which is which is which is taking electrons from water and driving up the whole process is red light which is
00:29:54not energetically %HESITATION decreased from blue light has far more energy in it than than red lights does so you'd assaults on from first principles that I'm actually colorful does absolutely liked as well as as John said but he's not using that wavelength %HESITATION and the reason is not
00:30:12clear but it may simply be the destructiveness of UV room blue lights %HESITATION you know it can damage our own writing this and so on as well there are issues with with high higher energy wavelengths of light so I think it's it's it's ended up with red partly
00:30:27because that's the the wavelengths that chlorophyll absorbs and partly because selection has adopted the the wavelengths of chlorophyll absorbs to being the the gentlest on on the plant itself is is less likely to do damage if you're absorbing light that wavelength cooling move on to and a section
00:30:46on the evolution because suddenly news Sunday I'm how has the need to such and such influence the evolution of plants in different sort of environments well because all plants need to photosynthesize to to make their own food to live and what's really interesting is planted all kinds of
00:31:04places photosynthesize so think about the back of Katie's the back of deep caves have photosynthetic organisms in them and so so what what has happened over over the course of evolution is that the plants that occur in particular areas have have developed structural structural elements of of how
00:31:24the leaves are that that all you could say optimize but they make photosynthesis possible so think about a plant for example in the in the very dark rain forest understory the light that comes in there is mostly those very long wavelengths the red wavelength but only comes in
00:31:39some flex and many plants in the rainforest understorey have a a red layer on the underside of the leaves and people for a long time wondered why this was and it's actually very striking in in deep rainforest plants and and %HESITATION David levy did some work in the
00:31:53nineteen seventies and published a really nice paper where they showed that that what happens in this anthocyanin layer is that it it reflects more it reflects light back into the core classes they get more of that of the of the little light is coming through they get a
00:32:08bit more anthocyanins are pigments that we see is red so they're absorbing everything except the red but anthocyanins so they're they're reflecting it back into the car plus in those rainforest plants but they also protect I'm Clark chloroplasts from excess light in very high light environments so plans
00:32:27to do a huge number of different things with the pigments in their cells and the structure of the cells which focused light in that some that are all driven by evolution because if you think about it what evolution is doing is it's maximizing the production of offspring so
00:32:41if you are a plant and you photosynthesize well grow well produce lots of seeds the jeans that you have the characteristics that you have we passed on to your offspring which is how evolution gets driven in an individual plants doesn't necessarily involve during its light it's all done
00:32:57through reproduction to the next generation and you think about the diversity a diversity of of structure in plants that's really driven by the ability to make food and grow in different kinds of ways think underground what we know about the yvolution his ship photosynthesis itself when when you
00:33:17thought to have emerged well this is quite a lot of controversy eight eight arose from the the very first forms very early on three and a half billion years ago but those films did not use water as the electron donor they use things like hydrogen sulfide and I
00:33:34and and and and the products that state they produce they they so if you if you're using I am as an electron donor what you're leaving behind his %HESITATION is is rusty Aryan which precipitates out of the oceans and forms banded iron formations which of the major sources
00:33:49of I and all the weed using today so you know some of the big mineral deposits derive from photosynthesis and are evidence that photosynthesis was happening at that time oxygenic photosynthesis so she's splitting water and releasing the toxic waste oxygen probably arose between two and a half and
00:34:10three billion years ago is difficult to constrain us there's arguments about it you know they that the arguments are based on the date that the ratios of different isotopes of different items is quite abstruse %HESITATION and we have to assume that measurements taken in one rock in one
00:34:29place or in some way representative of the whole planet which is usually not true so there's all kinds of difficulties with constraining we know for sure it happened as John said by two two point four billion years ago because we see this tremendous catastrophe so we have a
00:34:43snowball us at that time the entire planet froze over around town with Tommy on now what about two point four billion years ago Serbian several episodes of of the snowball us across of history I'm probably will happen that was as oxygen was being released it oxidized methane being
00:35:02produced by other bacteria %HESITATION and maintains a greenhouse gas and as it as it stripped out of the atmosphere the temperatures plummet and the other thing we see around that time is %HESITATION is the oxidation of rocks and so on on on the continent so we see buckle
00:35:18red badge basically rusty I am everywhere you're not going to come back to you again a talk about the structures in plant cells knows coracle in even restrictions hundred plants to gain the structures when went well they they acquired them the question of mergers and acquisitions and chloroplast
00:35:36Willa cyanobacteria %HESITATION a larger cell %HESITATION discovered that if it enters into an intimate partnership with a sign a bacterium it had a free supply of food and also oxygen full the term restoration %HESITATION I think there's really no doubt about that know when I was an undergraduate
00:36:03student this was regarded as a sort of flighty flaky left field proposition you know %HESITATION but no with %HESITATION for all sorts of reasons they really no escape from the fact that the the car class originated as an endosymbiont assembling within missile %HESITATION and that simply won't resembled
00:36:25very closely what we know today as cyanobacteria I've given the Senate died for this and it wasn't within within a sort of seven hundred million yeah something like well I think Nick already said one point five billion and I'd I'd go I go with it that's okay yeah
00:36:41I mean I it's because they're you know they're no fossils of this kind of thing to date in rocks it must've happened various reasons for knowing thinking it must have happened Nick cannon Sunday what one of ya emergence of the first for this is a vote for me
00:36:57anyway measure the first photosynthetic organisms how did it affect the development the lady development of life on earth well I I I mentioned the the the the snowball us in the great talk station events and so on after that you I mean ten twenty years ago we would
00:37:16have thought we did think that %HESITATION once oxygen level started picking up in the atmosphere everything sort of change but actually it didn't take all stuck in a rut for another billion years or so the million boring you have not boring billion is called the nothing really happened
00:37:31actually company sells arose in that time as John was saying the acquisition of chloroplasts and so on happened in that time there's very little in the fossil record we do see foxholes but %HESITATION you know we can't really constrain that they the sequence of events that happened but
00:37:49then at the end of this boring billion we we go into another global upheaval of of more snowball us and so on and then right on the back of dance is the company explosion and the appearance of animals really for the first time in the fossil record now
00:38:07this again lots of debates about what was happening but one thing was fairly certain about his steps oxygen was produced at that time by the by plants a terrestrial Alki and so on rather than just sign a bacteria and that gave the animals the energy they needed and
00:38:26that time is well becoming explosion is just over half a billion years ago five hundred and fifty million years ago getting closer yes is remarkable is that the three three and a half billion years of our history you know is bacteria and I'm very simple cells and then
00:38:40suddenly with the company explosion you see the first real real animals Sundin up would you give us some sense of the places photosynthesis has in ecosystems in general on that in the I'm not in the US as a whole well I think this is itself as we said
00:38:57drives drives life on earth essentially so it drives ecosystems and it probably drives that the composition of ecosystems as well if you think of what an ecosystem is it's all the organisms in a place and the relationships between them and because so many heterotrophs depend upon offer troops
00:39:13which of these photosynthesize in organisms for their daily lives and their food and then other heterotrophs depend upon those so we depend on wheat beef which is ahead for truck which is eating grass so we actually are eating sunlight via this complicated sort of %HESITATION submission about talented
00:39:30in that room yeah basically sort of but I think I think it is so so really photosynthesis is driving %HESITATION structural complexity in plants because of of involving structural complexity to be able to coworker and harvest light which is the resources and then those those relationships between things
00:39:50that live on those plants are also driven by that complexity of plants was quite it's a tangled web as Darwin said what to Joan Allen windage on his first talk to investigate the process of photosynthesis well you know the the great step in in in chemistry and biology
00:40:07was Joseph Priestley %HESITATION others whom Nick has written in his book oxygen only seventeen seventy two Priestley pubs published a paper an investigation of different kinds of and because he knew some sort of a is necessary for life another source of and would extinguish life and to the
00:40:30discovery of photosynthesis is with good reason ticked off to priestly in seventeen seventy two %HESITATION and the mouse and the most the most months when I was in the bell jar the most in the Belgian I'm I'm gonna minute could hear do we have time for this will
00:40:48we have to rush with maybe a good it's a big one I flatter myself that I have accidentally hit upon a method of restoring a which has been injured by the burning of candles and that I have discovered at least one of the restorative switching nature employees for
00:41:03this purpose it is vegetation one might have imagined it since common error is necessary to vegetable as well as animal life both plants and animals had affected in the same manner and I knew that I had that expectation when I first put a sprig of mint into a
00:41:19glass Joe standing inverted in a vessel of water but when it should continue growing there for some months I found that the end would neither extinguisher candle normal was it a tool inconvenient to in my house which I put into it that is the discovery of oxygen in
00:41:38the discovery for the synthesis in one experiment what a wonderful way to end your very much you got it all in John thank you very much thanks very much to John Allen sent an up and they claim next week we'll be talking about the Rubaiyat of Omar Khayyam
00:41:51thanks for listening and the in all time put costs get some extra time now with a few minutes of bonus material from Melvin and his guests long and complex process deliver the central out from yes I think I think Kim I mean are you a note to the
00:42:09I mean I I I I agree with everything he ever thinks and please accept the in the life of that came over in that way and the point really is a force of troops right you'll eventually correct I mean but you did say early on all photosynthetic organisms
00:42:29all or to prove it link build themselves up it's not true my group of microbiologists would insist on in fact yeah that's true that's for your also so I'm I'm in I'm in case of banking on that note we're off at right yes you must be to list
00:42:48little extra bit goes on as a PS in the podcast okay well just I think they can just just tell me tell me if this gets boring look let their two things you can actually be bought for billion yes yeah sure then there was a few minutes searching
00:43:04for things you can ask about any living creature number one where does it get its energy and is it a photo truth getting attention from lights or is it a chemo truth getting its energy from food each month so much energy filter trove with unknown in the United
00:43:24States will be there tonight absolutely final so that's the energy no photosynthetic organisms of photo troops but they don't have to be ordered for his they can get the energy and still eat food that might be too complex for taxonomists that's too much of a I'm I'm really
00:43:41not I'm not trying to you know try to hold on I would not wish to humble humble before planting textile image to actually knows knows about plans to show you but the second thing you can ask about any living organism is where does it get it stuff that
00:43:58it makes itself from does it apparently Janet from No Way will actually we know pluck it from the N. it sent a bolt of truth or does he get it from other living things hetero trove of the feeding that that's a possibility will hatred folks know that all
00:44:15flew to hatred troops to get the energy from light but they still eat food indeed other organic compost to assimilate the other thing that we're almost there the other a verse of the is there also chemo automotive truths which organisms which not interested in light they lived deep
00:44:35in one of those events eventually the chemo or to troops that get the energy from chemical reactions but they fixed CO two and make complex makes not just like yeah so that's a bit more a bit of a wider context at schools and they are now but I
00:44:52think what that I mean that's what that's what always amazes me is that life on earth is absolutely incredible the number of different ways in which organisms make their living survivor when I went to London looking at the prices doctor Johnson said that when people make it look
00:45:11as we said enough about the sun and another fascinating it is at all the other civilizations whether it's raw in Egypt all the sun god and now stakes that they headed by one from the beginning to the end I don't know what cricket I have some immediate perception
00:45:26that the sun was the source of all life and it right when it rises life begins in the seasons of tools and away from the equatorial reasons you worship the sun when it begins to appear should exert its strength in the spring is remarkable isn't it interesting is
00:45:41human well the correlation between the sun and growth especially in temperate zones it's got to be very it's very obvious one of the things I don't think I quite got across is that you know you think plants produce oxygen animals consumers in the US of complete balance and
00:45:56so nothing changes that's why you have that boring billion %HESITATION is only when you know if if we dine with buyers and will not stand kind of broken back down to CO two an option again as an a and I'm Walter again if we just buried intact as
00:46:12a possible fuel in effect then the oxygen it would've oxidize use left over in the at and so did the dynamic of revolutionary time is nothing to do with how much photosynthesis the raise is to do with how much companies buried Sosa geological process rather than really a
00:46:27biological process would help the world appeal got buried yes rolling it would end up with lots of oxygen in the air and everything with the three homes are I was wrong they are not off the hook tea or coffee ready there are many more radio full onsen discussion
00:46:47programs to download for free find these on the website of BBC dot co dot UK slash radio full

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