Posts Tagged ‘photosynthesis’
deciduous and evergreen: pourquoi?
star magnolia (Magnolia stellata) – I think. Thank you, internet
It’s now more or less officially spring, and leafless trees are blossoming, like the one across the lane from my new home, as pictured. So I’m wondering how they have the energy, and more broadly, why do some trees lose their leaves seasonally, and others not? I’m no expert on trees, and I hope, before this piece is finished, to identify this one, but at least I know it’s deciduous, I think.
I also want to know how this deciduous and evergreen dichotomy relates to photosynthesis, as surely it does. So, of course, I must look it up. Surprisingly, Oliver Morton’s Eating the Sun makes no mention of the evergreen-deciduous thing, but then I likely wouldn’t comprehend his explanation…
But here’s a photosynthesis formula that I can more or less comprehend:
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Which can be roughly translated as: six lots of carbon dioxide (from the air) plus an equivalent lot of water (from the soil), plus solar energy, makes glucose, and starch. The starch, the carbohydrate, is stored in the roots, trunk and branches. Deciduous trees shed their leaves in autumn, and enter a period of dormancy – reduced metabolism, which slows or stops growth. Presumably energy is expended, though, in the production of blossoms. It’s a risk worth taking, however, because blossoms exposed to the open air can be seen and more easily approached by pollinators and can have their seeds blown by the wind.
I’m guessing that evergreen trees are mostly located in dense forests, which tend to create their own microclimates, less susceptible to seasonal change. And they’re more of a thing in the tropics, where the weather’s always – tropical, more or less. And the leaves of evergreens tend to be thicker and spinier. Ms AI tells me this:
Evergreen tree leaves—whether needle-like or broad—are uniquely adapted with thick, waxy outer layers and robust cellular structures that minimise water loss and resist freezing. Instead of shedding all foliage at once, these trees retain functional, chlorophyll-containing leaves year-round, slowly replacing them individually over several seasons.
I’m hopelessly ignorant about tree and plant types but I’ve found a website that will freely inform me (or try to) of the identity of any tree or plant I present to them via a photo I’ve taken. Instant learning! I’m quite excited.
Apparently some individual tree leaves can live for over twenty years, and these leaves ‘tend to be tougher and thicker, and more expensive to build’, according to a Macquarrie Uni article, referenced below. Other interesting facts are that ‘conifers and other evergreen trees make longer-living leaves the closer they are to the poles’, and ‘deciduous trees do the opposite. Their longest-lasting leaves are found at the tropics’. It’s all about maximising carbon absorption. If you’re an evergreen conifer in poor soil and facing a long harsh winter you’ll need to make a long-term investment in your leaves, but if you’re a deciduous maple you’re best to create new leaves quick-smart that will capture the summer sunlight before dropping in autumn, and that means investing in fast-growing, cheap but flimsy leaves. I’m more or less paraphrasing here.
So I’ll make this piece a short one, but I’ll be taking more photos in the neighbourhood and trying to learn more about blossoms and soil and climate and photosynthesis for future posts and my own delectation. I’m feeling Spring in my step!
References
A Tree Blooms Without Photosynthesis (Leaves)? The Science Behind Spring Blossoms
mostly about Ukraine and Russia and hopes for a better future
just some blokes
As a generalist sort of pseudo-intellectual in quiet and calm Australia, I’m tossed between the best and the worst stuff to focus on, mostly in the top hemisphere of our planet, as if I know which way is up. War and Russia and the USA under Frump (talk about the world’s worst-ever own goal), and the grim future with global warming, and the runaway rich-poor gap in so many countries, and the worries over the rapidity of AI developments and who’s controlling them, and then JWST (no longer Just Wonderful, it seems) and the future Nancy Grace Roman and all the exoplanets to come into our purview, and dark matter as structure or whatever, and the Hubble Tension, and gravitational lensing trickery, and then back down to Earth and its rubisco abundance….
So I’m re-reading with difficulty, but also great admiration tinged with annoyance, Eating the Sun, which I’m committed to finishing even without full comprehension, for who has such a thing, but I’m also reading a vastly different book, not as an antidote (for that would require some planning which I’m incapable of), but because I try to contain multitudes, as we all do to some degree (do we?).
The Story of Russia, by Orlando Figes, was published in 2022, so presumably was written, or mostly written, before the current attack on Ukraine, but is of course being read by me with that ‘special operation’ in mind. Needless to say, I despise Mr Pudding as much as I despise Frump, while also realising they can’t help but be who they are. They are the products of very different environments, and have both exploited those environments very effectively indeed.
What I’m learning from Figes, much of which I sort of knew already, is that Russia has long defined itself in opposition to Europe – or rather its leadership has. Russia is vast, and its multitudes contain vast differences, but they’ve never really had a voice, and it seems that they don’t want to, or they don’t know how to. It doesn’t really have a single definable ethnicity, and it defines itself more by class than anything else. The owner class, the worker/peasant class, the political class. It has never experienced anything remotely close to democracy, and I think it has, historically, been more open to, or more easily persuaded by, that vague, hopeful, egalitarian-sounding concept called ‘communism’, in which you don’t even have to vote to be part of the government, somehow or other. The people seem to have been convinced that Europe is their enemy – evil, presumably debauched, and rapacious. Out to get them, to steal their identity, to rub them out as a proud ethnicity. Certainly this is the kind of propaganda that Putin makes use of, but what does that bizarre much-murdering individual really think? For example, he never for a moment believed that Ukraine was full of Nazis, but he did believe that this line would work in Russia. So what does he think of the average Russian, then, and is he correct, or at least close to it? How popular is the bloke? Presumably not as popular as five years ago, but even so…
As I learn, through Figes, of Russia in 1917-1920, with Bolsheviks, Mensheviks, Social Revolutionaries (a different group apparently) and of course Germans, at a time when so much was up for grabs – Ukraine, Poland, Estonia, Finland – when Petrograd, that all-too-European city, was switched out for Moscow, the pride of Russia, as its capital – everything was changing, Tsars gone forever, and supposed freedoms being fought for with ever-increasing brutality by the new men, Lenin, Kerensky, Trotsky and the grotesque Stalin. All seeking to impose something entirely anti-European while looking over their shoulders at the European powers with a weird and dismal kind of love-hate. And that’s a theme, of course, that continues to this day. A kind of spurned lover’s hatred for the west, and a desperate need to find some superiority to cling to. This appears to be Mr Pudding’s obsession, and he really seemed to think that some weakness, or some Old Russian-ness in Ukraine would deliver it to him. He has under-estimated the depth of contempt that Ukraine has for him – for him personally, rather than Russia itself. And of course he has also under-estimated that country’s western advancements and passions, as well as the real difference that separation from the horrors of his regime has wrought. He has absolutely nothing positive to offer Ukrainians.
One can only hope, for Russia’s sake, that their 73-year-old dictator is their last. They deserve so much better than the thieving, murdering, backward-facing lot that finally emerged from the dissolution of the Soviet Union in the late 80s and early 90s. All that hopeful sense of glasnost and perestroika was brutally shattered. I’ll be interested to read what Figes thinks of Russia’s future in the final chapters of his book.
Reference
Orlando Figes, The story of Russia, 2022
Oliver Morton, Eating the Sun, 2007
more on photosynthesis: stuff about rubisco, or not
don’t ask
So in my wild wanderings on this topic I’ve been informed by a close friend that rubisco is key, and research is ongoing. So, starting off with my key text, Oliver Morton’s Eating the Sun, and a video on rubisco that’s been drawn to my attention, I’ll keep making attempts to educate myself.
So, nitrogen is essential to all living organisms, and our atmosphere is mostly nitrogen – just over 78%. It’s essential to proteins and DNA, but apparently it isn’t something we can directly access. There’s an enzyme complex called nitrogenase, which some bacteria and archaea can produce, which is able to convert inert nitrogen gas into ammonia (NH3). However, nitrogenase falls apart in the presence of oxygen, so atmospheric nitrogen can’t be used by virtually all living organisms. Only anoxic organisms – generally very basic microbes (spoiler alert – nitroplasts) – can make use of it. So, it has generally been a rule of biology that no complex organisms can utilise nitrogen, but a new bacterium was discovered quite recently, or rather its DNA. That’s to say, samples of seawater were examined for the presence of nitrogen-fixing bacteria. What was initially found, in the 1990s, in a search for a key nitrogen-fixing gene, was genetic material, without the organism it belonged to. The searcher, or researcher, felt that he had a good idea what the missing organism would look like. A hunt was on to find this organism, which left its ‘fingerprints’ everywhere, but it took years to find it, all they could find was DNA with a missing owner (I’m relying heavily on a video referenced below for all this). What they did find was quite strange – its DNA didn’t seem to contain the genes for photosynthesis. And this DNA turned up all over the place, ‘complete’ with missing genes – a lot of them, some 80% of its entire genome – which seemed to make its very survival questionable. But then it was worked out that the DNA was inside a species of algae which was hosting it. This algae, Braarudosphaera Bigelowii (Bigelowii for short), was being investigated in Japan by a female scientist, partly because of the symmetrical beauty of its shape at a particular developmental stage. She eventually managed to culture the algae (the video tells the story beautifully and movingly), and found something odd amongst the expected parts, almost like a separated container.
The Japanese researcher came across work from the team who had discovered the DNA with the missing host. It was generally a shock to both sides, but they were able to work together and discover what was effectively a symbiotic process, though the video on this suggests that the process goes beyond symbiosis, and is more like ‘two organisms fusing into one’, as with mitochondria and chloroplasts and their hosts. Bigelowii had become an organelle, dividing and growing at the same rate as its host. It was an important discovery, not only to add to the small family of organelles (it has been called a nitroplast), but to find an organism that effectively fed on nitrogen. Could this be used to produce nitrogen – which is currently produced in expensive and inefficient ways – out of the air?
So, this stuff about nitroplasts is quite recent, so it doesn’t get into Morton’s book to complexify it even further. And it’s the most complex book I’ve read – and I’ve read an awful lot of the bloody things. I can but give an example: this, about chloroplasts:
As they have spread out with and through their wormhole world, its chloroplast inhabitants have changed according to the requirements of the time-tunnels that they find themselves in; evolution applies in there just as it does out here. In some tunnels the chloroplasts are squadrons of small green capsules that still have the look of bacteria. In others they have evolved into swirling spirals pressed tight against the outer membrane like rifling in the barrel of a gun. Some are red five-pointed stars, one to a cell. But they are all descended from the same original ancestor.
There are many dead ends in the network – hundreds of thousands in every leaf that falls – billions of times as many in every fossil species bereft of descendants today. But the threads as yet unbroken are all but uncountable, and multiply still. All around us, moment by moment, the skein of wormholes pushes itself further into the future.
Oliver Morton, Eating the Sun, pp 209-10
Rifling in the barrel of a gun? I’ve managed to avoid going near such an item in the 70 years of my life. And I might know something about the look of love (or not), but the look of bacteria is well beyond me. Never owned a microscope, sadly. As for the rest, lovely writing but I can’t quite get a picture…. But, I will soldier on…
References
Oliver Morton, Eating the Sun, 2007
the photosynthesis challenge
c’est bien simple…
So I wrote last time about my non-career in science, with a promise to myself that I might try to get my head around photosynthesis. So, years ago I read Oliver Morton’s fiendishly difficult book, Eating the Sun, and all I clearly remembered about it was that there were two types, simply named type 1 and type 2, and that the processes are very very very complex, and took decades to unravel. And a feeling that it was all over my head. Or that one had to be there, in those labs, or chatting at science conferences with the experts, as Morton no doubt was, to have a chance of getting my dull head around it all. And yet, never say never…
So I’m rereading Morton’s book (published in 2007 – has more been nailed down about the processes since?), having nothing better to do – and that isn’t meant as an insult – and I’m currently about a quarter of the way through. What I note is that Morton intermixes the undeniably complex science with interesting character sketches of the major researchers and theorists, and descriptions of the mostly mid-twentieth century background of war and conflict (at least in this early part of the book). My aim here though is self-education, so I’ll be focussing entirely on the science as far as I can grapple with it. So there will be no names, just a lot of ‘this breakthrough led to a new avenue of research’, etc.
So, photosynthesis is about using sunlight as sustenance. Of course, water is also required, and CO2. The devil’s in the detail, and there’s an awful lot of it..
So, where to begin. Chlorophyll, I suppose. That’s the green pigment in the chloroplasts of plants and algae. They absorb light, mostly from the sun. But what does this mean? And how did we come to know this?
Chloophyll is green because the green area of the light spectrum is reflected, while blue and red light is trapped, mostly. So, though plants ‘eat’ sunlight, they don’t eat the green part of that light, which is fascinatingly counter-intuitive.
As to these chloroplasts, these key sub-cellular elements in plants and algae, they’re a product of endosymbiosis, the colonisation of eukaryotic cells by earlier microbes – bacteria or their ancestors. Mitochondria, the engines of ATP through oxidative phosphorylation (wateva), are another such product.
Which brings me to photophosphorylation in plants, as useful and interesting a starting point as any. This process, originally called photosynthetic phosphorylation, might be expected to be carried out by mitochondria in plants, as it is in mammals, but plant biologists noted that ‘the leaf cells with the greatest number of chloroplasts – the cells that do the bulk of the photosynthesis – contain remarkably few mitochondria’ (Morton, p76).
Phosphorylating, as I understand it, involves adding a phosphate to ADP (adenosine diphosphate) to create adenosine triphosphate (ATP), the principal ‘energy molecule’. Another such molecule is NADPH (Nicotinamide Adenine Dinucleotide Phosphate), of which more later, perhaps. They are both important in plants, and are key to what became known as the Calvin-Benson cycle, a set of chemical reactions (independent of light) within chloroplasts as a part of photosynthesis. These reactions convert CO2 from the atmosphere into sugars for energy.
There are apparently two main stages to photosynthesis, the light-dependent stage and the light-independent stage (aka the Calvin-Benson cycle, or even the Calvin-Benson-Bassham cycle). The light-dependent stage occurs inside the thylakoid membranes of the chloroplasts. Here’s Wikipedia:
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: granum). Grana are connected by intergranal or stromal thylakoids, which join granum stacks together as a single functional compartment.
In thylakoid membranes, chlorophyll pigments are found in packets called quantasomes. Each quantasome contains 230 to 250 chlorophyll molecules.
So that’s something about thylakoid structure. Now to function. Or maybe not – it’s all so complex. The thylakoid proteome (set of individual proteins) consists of at least 335 protein types, of which 89 are in the lumen or central cavity. At this stage it’s calculated that about 42% of these proteins are involved in photosynthesis.
Jumping away from all this, it’s important to note that for us mammals, the essential value of photosynthesis is that it creates, or releases, oxygen. Think of the great oxygenation event, mainly involving oceanic cyanobacteria, ‘about 2.4 billion years ago, shortly after the end of the Archaean’, according to Morton (p175). So how does that oxygenising aspect of photosynthesis work?
But I was going to write about the light-dependent part of photosynthesis, requiring sunlight and water. It’s called photosystem 1, and Wikipedia calls it ‘a vital membrane protein complex that uses light energy to transfer electrons from plastocyanin to ferredoxin, producing NADPH and helping generate ATP.’ So, digging slightly deeper, plastocyanin is ‘a small copper-containing protein that acts as a mobile electron carrier in the photosynthetic electron transport chain of plants, green algae and cyanobacteria’, and ferredoxins are ‘small iron-sulphur proteins that act as electron carriers in a wide variety of biological redox reactions’.
Now, NADPH is, of course, ‘the reduced form of nicotinamide adenine dinucleotide phosphate’ which acts as ‘a key electron donor and energy carrier’ in various processes, including photosynthesis. So, my guess is that these movements of electrons create chemical changes, and a moment’s research tells me that’s what redox reactions are all about. In oxidation, electrons are lost, which takes the oxidation number up (the substance is oxidised), and in reduction they’re gained, which takes it down, and the substance is reduced.
In oxidation, electrons are lost, which takes the oxidation number up (the substance is oxidised), and in reduction they’re gained, which takes it down, and the substance is reduced.
Ok so that’s enough for now, there’s so much more to explore – rubisco, the z scheme… I cannot help but feel that it’s not light yet, but it’s getting there, to non-paraphrase Dylan….
References
Oliver Morton, Eating the Sun, 2007