Ep 9 - The cell that ate the sun (photosynthesis)

A cell eats another cell… again.

But this time? It doesn’t just get energy — it gets the ability to make food from sunlight.

In this episode, we dive into chloroplasts, photosynthesis, and the moment life figured out how to turn sunlight and air into sugar.

Plants stop hunting. Animals don’t.

And every calorie you’ve ever eaten? It all traces back to this one ancient accident.

Transcript

Jackie 0:02

Hello, I'm your host Jackie Mullins and welcome to From Cells To Us, how the podcast where we figure out how life went from a single cell to complex creatures like us. Last episode, we talked about one of the wildest accidents in the history of. Life. A cell ate another cell, didn't digest it, and that mistake became the foundation of every complex living thing on earth. We talked about how mitochondria, your ancient bacterial power plants, and how that one accidental merger gave cells enough energy to do something they'd never done before. Get complicated. But here's the thing I left you with at the end of episode eight. Mitochondria aren't the only former bacteria living inside cells. There was a second merger, and this one didn't just change animal cells, it changed the entire planet. You know, again, because the organisms at the center of the story, you've met them before back in episode seven. They're the ones who filled the atmosphere with oxygen and almost wiped out all life on earth. The cyanobacteria are back, and this time, they're not destroying the world this time. They're feeding it. Let's get into it. So let's set the stage here. Let's take stock of where we are on our timeline. It's about one to 1.5 billion years ago. We are still in the pro to Zoic Eon, but the meso pro heroic era, to be specific, the eukaryotic cell has been established for hundreds of millions of years now. Mitochondria are. Fully domesticated the merger. We talked about last episode, ancient history at this point and earth. Well, it looks almost identical to how we left it. The sky is a deeper blue now because oxygen has been building for another billion years and it shows it's still not the saturated blue we know today, but it's getting closer, more familiar. The oceans are still largely empty of anything you'd recognize near the surface. Greenish tinges. From vast mats of microbes and early algae floating in the sunlight, but deeper down, still dark, still anoxic. Still sulfur rich. The deep ocean hasn't caught up yet. The land is still bare rock, still silent, still empty. If you stood on the shore, you'd think nothing had changed since last episode. No plants, no animals, just wind and rock and water, but there's something worth noticing. The continents don't look anything like what you'd recognize from a map. And I know what you're thinking. Pangea, right? That's the Supercontinent. That's the one everyone knows. But Pangea wasn't the first. It wasn't even close to the first. At this time, the continents are slowly grinding together into a super continent called Nia a giant landmass sitting in the middle of a vast global ocean. There was no Atlantic, no Pacific, as we know it just one enormous continent surrounded by one enormous sea. It won't fully assemble for another a hundred million years or so, and it'll eventually break apart again. Because that's what Earth does, assemble, break apart. Reassemble Earth has been playing this game for billions of years, and Pangaea was just the most recent round. Geologists actually have a name for this period. They call it the boring billion, a stretch of roughly a billion years where Earth Surface barely seemed to change at all. But boring is relative because if you jump off your boring rock and swam down, down, down into those greenish waters, something was quietly happening that would eventually cover every continent in green, feed every ecosystem on the planet and make every meal you've ever eaten. Possible. It didn't look like much from the outside. However, to us, microbes never really do. So what was happening? Well, I wanna start with something that I think gets completely glossed over in middle school biology and deserves a proper moment of appreciation. Plants are not one organism. I know that sounds weird. Bear with me. You look at a tree and you see a tree, one thing, one organism rooted in the ground doing its tree business. Very chill about everything as trees tend to be, but zoom in, not just to the bark Further. Pass the bark, pass the rings, pass the wood itself down to where your outstretched finger touches the tree. Under that one fingertip thousands of cells. You are now at the cellular level and what you're actually looking at is not one organism. It's a collaboration, a merger, a community of former separate organisms that have been living together for so long, they forgot they were ever separate. Just like you, except under your fingertip, those tree cells, plant cells, well, they have something extra Plants aren't running one ancient bacterial merger. They're running two simultaneously in every single cell. You have mitochondria, ancient bacteria, power plants that moved in 1.5 billion years ago, as we talked about last episode. Plants have those too, but plants also have chloroplast, which were also former bacteria, specifically former cyanobacteria, and the name probably sounds familiar. There's a reason for it. We spend a significant chunk of episode seven talking about them, the cyanobacteria. The ones that figured out how to split water molecules using sunlight, the ones that filled the atmosphere with oxygen as a byproduct, the ones that triggered the great oxygenation event and nearly wiped out all life on Earth. Those guys, they didn't just survive the world they created. They didn't just adapt and carry on. They also ended up inside cells permanently running photosynthesis. As a service for their host, the most wanted criminals in the history of life became the most important food producers in the history of life. Same organism, different era, completely different role. We keep coming back to this theme. One organism's apocalypse is another organism's, power plants. So how did Coral plast get in there? Well, first, let's remember what cell we are talking about here. At this point, there are pro caros. The studio apartments with no nucleus, no mitochondria. And then there's the eukaryotes that have a nucleus, a mitochondria. They're the big mansions, right? And they grew super big due to extending blebs, and they are eating other cells. So one of the eukaryotic cells is swimming around, churning out a TP with their mitochondria at about roughly 1 billion years ago. Then it engulfed a Sano bacterium that was its lunch, which at this point was honestly a pretty normal Tuesday for cells that had figured out phagocytosis cells were eating other cells constantly. This was basically the whole game at this point in history. But this time, just like with the mitochondria, something went differently. Cyan o bacterium wasn't digested. It survived inside the host cell. Now, why did it survive? Same mystery as before. Maybe it had a way of resisting digestion. Maybe the host cells machinery malfunctioned. Maybe it was a fluke. We don't know exactly what we know. Is that it happened and it stuck, and instead of being a threat or a burden, the Cyan O bacterium turned out to be very valuable because it could do something the host cell couldn't do. It could capture energy directly from sunlight. Can you imagine eating lunch, not digesting it properly? Then one day just realize you're super energized just by going outside, you know you don't need to eat lunch anymore. Can you imagine how different our houses would be built? You know, all tempered glass skylights everywhere. No kitchens just a platform that moved you up to the roof. To gulp down those delicious photons. Well, that's basically what happened with these cells. Suddenly, the host cell with cyanobacteria in them had access to a completely new energy source. Sunlight, which I want to be very clear about. This is absolutely everywhere and completely free. The sun is just out there every day handing out energy to anyone who can figure out how to grab it, and cyanobacteria knew how to grab it. So cells that kept it alive could make their own food from sunlight. Cells that destroyed it, couldn't guess which ones thrived. Guess which ones reproduced? Guess which ones eventually became every plant and algae that has ever existed on this planet. So the partnership stuck. The cyanobacteria gradually lost its independence over hundreds of millions of years. Shed genes that didn't need it anymore, transferred others to the host cells Nucleus, got smaller, more specialized, got more integrated until it wasn't cyanobacteria anymore. It was a chloroplast, an organelle, a permanent resident, a former free living organism, now running photosynthesis as a full-time job inside plant cells, never leaving. Completely domesticated, just like mitochondria. Two mergers. Same story. Different outcome, and this is where two lineages of eukaryotic cells start going in very different directions. One with chloroplast, one without that difference. That one ancient merger, roughly a billion years ago, would eventually produce every plant on one side and every animal on the other side. And before we move on, I think it's worth knowing these first cells that took on photosynthesis. They still needed minerals, carbon dioxide and sunlight, gave them energy and carbon, but they still needed nitrogen, phosphorus, sulfur, and iron to make amino acids, D-N-A-A-T-P and enzymes, because remember, they still needed to run the central dogma, the DNA to RNA to protein pipeline that we covered earlier. Rick, Mary, and Tina still had jobs to do, and this is still true of today's plants, right? But today's plants get these minerals from the soil or water, depending on where they live, or if they're indoor plants, perhaps the fertilizer you give them. Or if you're me, you can merely look. At a plant and somehow take its will to live despite giving said minerals, water, and sunlight, the world's lamest superpower. So photosynthesis gives you the flour and the sugar for your cake, but you still need eggs. Baking soda, vanilla salt, the chloroplast solve the energy problem. It didn't solve every problem. You know, think of it like this. Photosynthesis gives you the flour and sugar for your cake, but you still need eggs, baking soda, vanilla, and salt. The chloroplast solved the energy problem, but it didn't solve every problem. They got those extra ingredients by absorbing minerals from their environment and still occasionally consuming other cells. But they didn't need to rely on hunting nearly as much as eukaryotic cells without a chloroplast. They had options. That one difference, that one ancient merger, roughly a billion years ago, a eukaryotic cell swallowing a cyanobacteria and putting it to work instead of digesting it. That single event was the deciding factor between what would need to move and what could stay still. Animals move because they have to. They need to find food, hunt it, chase it, catch it. Plants don't because they figured out how to make food from wherever they're standing. Every lion that has ever sprinted across a Savannah, every bird that has ever migrated thousands of miles, every human that has ever tracked a buffalo for days harvested crops, or, you know, gotten up to go to the kitchen. All of that motion, all of that complexity of movement traces back to the fact that our ancient ancestor didn't get a chloroplast. And every tree that has ever stood completely still for a thousand years, that stillness traces back to the fact that theirs did a billion years ago that was decided by accident in an ancient ocean, by a cell that was swallowed by something it didn't digest. That was the deciding factor that led to two very different ways of surviving, chasing energy or capturing it. So how do we know that the chloroplast used to be a free living bacteria? Well, here's the beautiful thing about the chloroplast origin story. The evidence is almost identical to the mitochondria evidence. Because it's literally the same process. Chloroplasts have their own DNA separate from the plant cells, nuclear genome. Just like mitochondria, chloroplast reproduce by binary fission dividing on their own independently of the cell exactly the way bacteria reproduce. Just like mitochondria, chloroplast have double membranes. The outer membrane is a remnant of the original engulfment event, the inner membrane, the original bacterial membrane. You can still see the seam. Just like mitochondria, chloroplast, are the right size, the same size as a cyanobacteria? Not a coincidence. Just like mitochondria, and here's the callback. We know exactly what kind of bacteria chloroplast used to be because cyanobacteria are still alive today, still swimming around in oceans and lakes and soil. Still doing photosynthesis the same way they've been doing it for over 2 billion years. And when we compare the DNA of modern chloroplast to modern cyanobacteria, the match is overwhelming. The family resemblance is unmistakable. These are the same organisms. If they did a 23 and me, they would definitely each get an email saying, you have a cousin match. One branch stayed free living. One branch got engulfed and became an organ. The organisms that almost destroyed all life on Earth 2.4 billion years ago are now living inside every plant cell on the planet, quietly feeding the entire ecosystem. If that is not the greatest villain to hero redemption arc in history, I genuinely don't know what is. Now, perhaps you're asking yourself, if there are free living chloroplasts as cyanobacteria, why aren't there free living mitochondria? Well, there are not mitochondria themselves, but their relatives are still out there. They are called Alpha Proteobacteria and they are still living freely in oceans all over the planet and cyanobacteria. The relatives of chloroplast are still out there too. Still doing photosynthesis still. Pumping oxygen into the atmosphere like they've been doing for billions of years. So both groups still exist. They just took different paths. How I pictured it is like wolves and domesticated dogs, right? First you have the wolves. These are the free living organisms, independent self-sufficient, doing everything on their own. That's modern cyanobacteria. That's alpha Proteobacteria, mitochondria's cousin, they're still out there, still thriving, still wild. And then you have the domesticated dogs. You know the golden retriever on your couch? That's mitochondria. That's chloroplast. They moved in. And made themselves indispensable. They gave something in return energy, food, and over time they gave up their independence completely shedding gene transferring control, becoming so integrated they can't live on their own anymore. Just like that golden retriever, unless it was shadow and he could obviously hold his own. However, there is also this weird middle group, we'll call it. The feral dog, and this one is worth spending a minute on because it's genuinely a wild story. So there's a bacterium called Rickettsia, and it causes Rocky Mountain spotted fever and typhus. And at first glance, it just seems like a nasty pathogen, but look closer, and it's something much more interesting than that. Rico is essentially caught mid domestication. So it's not a wolf, it's not a domesticated dog, it's a feral dog. It's a living snapshot of what the mitochondria ancestor might have looked like halfway through the process of becoming an organelle. A bacterium, frozen and evolutionary time between wild and domestic, between free and captive between partner and parasite. Sounds like a Shakespearean tragedy, right? Well, here's why. Like mitochondria, esia cannot survive outside a whole. It got so dependent on living inside cells that it lost the ability to live independently. The outside world is now lethal to it. Just like mitochondria and like mitochondria, ESIA has shed most of its genes. A free living bacterium has thousands of genes. Esia only has 800 mitochondria, 37. Esia is literally partway down the same gene shedding pathway that mitochondria went all the way down. You can almost see the trajectory. If Esia kept going in the same direction for another billion years, shedding genes losing independence, becoming more integrated, would it eventually look like mitochondria? Maybe, but probably not because of one crucial difference. A TP mitochondria make a TP and give it to the host cell. That's the whole deal, right? That's why they got kept. That's why cells maintained the relationship and thrived Rico. Castilla does the opposite. It steals a TP from the host cells, same molecule, opposite direction. Mitochondria export energy, ESIA import it. That one reversal, give versus take is essentially the difference between a powerhouse and a disease. And here's the other wild thing about rickea. It didn't wait to be eng golf. It actively invades cells. It hijacks. The hosts own cytoskeleton, which we'll get into in episode 10, and uses them like a propulsion system to launch itself into neighboring cells. It's essentially commandeering the cell's own infrastructure to spread, which means rickea figured out how to get inside cells and how to move in between them, and how to avoid being digested. It did everything right except it took instead of gave, and that made all the difference. And because of that, it never became a partner. It became a parasite. OCEA is what mitochondria could have been if that ancient bacteria had been selfish, which is maybe the most profound evolutionary lesson, right? The difference between your most essential organelle and a disease that can kill you comes down to one thing, which direction? The A TP flowed the feral dog that moved in and kept stealing food and eventually got kicked out. But the one that started helping, never had to leave. So wolves, those are the free living alpha, proteobacteria and cyanobacteria Domesticated dogs. That's the mitochondria and chloroplast and the feral dog stuck in between a wolf and house pet. That's the three branches. Same family, wildly different fates. All right. Now we know how chloroplast got there, but let's make sure we actually understand what they do, because photosynthesis is one of those things that everyone has heard of but isn't exactly sure how or why it works. So I'm gonna jump to the future our present really quick, so that you understand the significance of the second merger, the significance of a eukaryotic cell eating another bacteria and keeping it around. Here's what you'll wanna know. Every living thing needs energy. We've established this over several episodes, and energy has to come from somewhere, right? It doesn't just appear from nothing. First law of thermodynamics, right? Energy cannot be created nor destroyed. Only converted animals us. Get energy by eating things. We consume organic molecules, sugar fats, proteins. Our mitochondria breaks them down through cellular respiration and makes a TP and that a TP is like quarters. Remember what our body actually runs on? We put in a hundred dollars bill into our mouth and mitochondria breaks it into quarters and distributes them where they're needed. And here's how that actually works at the cellular level, your mitochondria need two things to change that a hundred dollars bill into quarters. First, it needs glucose, and that's from the food you eat broken down by digestion and delivered through your bloodstream. Second, it needs oxygen from the air you breathe, picked up by your lungs and delivered through your bloodstream. And think about what our bodies have built. Just to deliver those two ingredients. Continuously, you mash up food, swallow it, it tumbles down your throat, through your stomach, through your intestines, nutrients getting extracted the whole way down. And we have proteins, little molecular delivery drivers, and they take those nutrients from your digestive system and bring them all the way to your cell's, mitochondria, without you thinking about it, without you doing anything except eating and breathing completely automated. And then there's the breathing. Since the moment you came out of the womb and took that first big crying breath of oxygen, it never stopped. Not once a continuous automated pumping of oxygen that you never consciously think about until maybe right now. Requiring about 20 trillion red blood cells acting as transport vehicles and one very important organ, the heart beating purely to move all of it through your body, every beat, every breath, just to get oxygen to your mitochondria. Those are extraordinarily complicated automated systems running every second of your life just to feed your mitochondria and mitochondria. Take these two ingredients and essentially burn the glucose using the oxygen, right? Not all at once, like an actual fire. That would be chaos, but in a very controlled step-by-step process that captures the energy and converts it into a TP and the waste products. Carbon dioxide and water, which is why you breathe in oxygen and breathe out carbon dioxide. The CO2, you're exhaling. That's the exhaust from your mitochondria burning glucose. You're not just breathing, you're venting cellular exhaust, which if you listen to episode seven, sounds familiar, right? You are a very slow, very organized fire with feelings. That's still true. Your mitochondria are running a controlled combustion reaction every second of every day. Glucose plus oxygen in a TP plus carbon dioxide out, round and round. Every breath, every heart rate, every thought. We are consumers. We need both ingredients delivered continuously or the whole system stops. Simple, but entirely dependent on finding something to eat. And something to breathe and our bodies aren't patient about this process. Within a few hours of not eating your blood sugar drops and your brain starts panicking. Your brain is only 2% of your body weight, but it demands 20% of your total energy, the most high maintenance organ you have with almost no energy storage of its own. Miss a meal and it lets you know immediately irritable, foggy, unable to concentrate. that's your brain throwing a tantrum because the a TP supply is getting low. Those snicker commercials hungry, grab a Snickers, right, are funny because they're true. Everyone has that one person they know that get absolutely savage when they're hangry. This is why if you go a full day without eating your glycogen stores run out entirely. Your body starts breaking down fat for fuel. Go several days and it starts breaking down your own muscle for energy. You are literally eating yourself from the inside. Weeks without food, organ failure, eventually fatal. We are, for all our complexity, entirely dependent on finding something to eat every single day without exception, If you think about it, we're basically a gingerbread house for ourselves. If you keep feeding it, everything's fine, but depleted of energy and it turns on itself, starts eating whatever it can find, which is probably one of the creepier ways to look at it, but. Not untrue. plants figured out something different, something almost unfairly elegant. They figured out how to make food from scratch with nothing but sunlight, water and air. No hunting, no searching. No anxiety about where the next meal is coming from. Just turn toward the light. And before we move on, I know some are out there sitting and thinking, but Jackie. What about fasting? I've been doing intermittent fasting for six months and I feel great. That's fair. Let's talk about it. Fasting works because of everything we just described. When you deliberately stop eating, you are essentially triggering those same starvation responses in a controlled way before you get to the dangerous part. In the first 16 to 20 hours, your glycogen stores deplete and your body makes the switch from burning glucose. To burning fat, insulin drops glucco rises your mitochondria. Switch fuel sources like a hybrid car switching from electric to gas, go a little longer. And something really interesting happens, your cells start a process called. Autophagy Which is basically your cells taking out their own trash, breaking down damaged organelles, recycling, misfolded proteins, cleaning house, some researchers think this cellular cleanup is one of the main reasons extended fasting seems to have health benefits. So fasting isn't really about starving yourself, right? It's about deliberately triggering biological processes. Your body already knows what to do. It just doesn't get the chance very often when food is constantly available. You know, having a conversation with your mitochondria about what to burn next, and giving yourselves a rare chance to tidy up. This would be like if our gingerbread house needed some fixing, right? Like if we took away food from the people living inside, just long enough for them to nibble on the damaged parts. Instead of on the house, because they don't wanna take out the structure. They're living in that house. If they have to eat the house, they'll start with the unnecessary parts first. Maybe that add-on that you didn't really need, or maybe there's a staircase going to nowhere. And once all that cleanup is done, you give them food, not your house. That's autophagy Cellular housekeeping funded by your own structure, temporary, controlled, and genuinely useful as long as you don't let it go too far. But, and this is very important before anyone starts fasting because a podcast told them to, there is so much more to consider than the basic biology I just described for one. Hormones and fasting affects hormones significantly, particularly of course more for women. And in general, some people don't handle fasting well and tend to overeat when they're not fasting, and without careful attention to nutrition, you can lose muscle mass. And fasting can genuinely be dangerous for people with certain conditions like diabetes. The human body is wildly complex. There is no fix all button. So at the risk of sounding like the end of a pharmaceutical commercial, please talk to your doctor before you start any fasting protocol. I am, but a simple podcaster who is excited to talk about mitochondria. Now, where were we? Plants, yes, while we're over here building an entire organ system just to feed our mitochondria. Negotiating fuel sources, scheduling, cellular cleaning days, plants just turned toward the sun. The nerve. They figured out how to take energy directly from sunlight and use it to build food from scratch, not consume food, not fine food, not hunt food, but build it from literally nothing but sunlight, water and carbon dioxide. Three things that are just floating around absolutely everywhere, costing nothing. Plants can construct glucose. They're just in the grocery aisle. Loading up on these three things and walk right outta the store. No cash exchange. No credit card. Just gathering things around them and using them for energy, sugar, fuel. Energy stored in a chemical bond. That's photosynthesis. So how does it actually work though? Photosynthesis happens in two stages, and stick with me. Stage one happens in these little stacked membrane structures inside the chloroplast called thylakoids, think of them as like a stack of pancakes inside the chloroplast. That is where the sunlight comes in. Sunlight hits the chlorophyll. Yes, I know we're all thinking it more like bourail. So sunlight hits the chlorophyll, which is the green pigment. This is the reason plants are green and it energizes electrons. Those small little guys surrounding the nucleus in an atom. Well, those electrons get passed down a chain of proteins, like a hot potato releasing energy. Each step, that energy gets captured and stored. And in this process, water molecules get split apart, just like cyanobacteria figured out back in episode seven. Same trick, same result. The oxygen that gets released when the water splits, that's what you're breathing right now, the exhaust of a chlorophyll. Stage two is called the Kelvin cycle. This is where the actual food gets made. The stored energy from stage one gets used to grab carbon dioxide straight out of the air and convert it into glucose. Sugar. Food made from literally nothing but air and stored sunlight. Carbon dioxide goes in, glucose comes out. So the full process is sunlight hits the chlorophyll. Water gets split, energy gets captured. That energy grabs carbon dioxide from the air and builds glucose, sunlight, and air turned into food. So my best analogy for this one, I couldn't think of anything too fun, but this one is pretty spot on. Think of it like a hydroelectric dam. First, you capture the energy by letting water flow through the spin turbines, storing that energy as electricity. Then you use that electricity to power a factory that builds something. Stage one captures stage two builds. The sun would be the water, and the ths are the turbines. The Kelvin cycle is the factory. And here's the part that gets me. Mitochondria and chloroplast are running opposite reactions. Chloroplast, take carbon dioxide, water and sunlight, and make glucose and oxygen. Mitochondria take glucose and oxygen and makes carbon dioxide, water and a TP. They are literally completing each other's chemical equations. The exhaust from. One is the fuel for the other round and round plants and animals locked in this beautiful chemical conversion that's been running for over a billion years now. I'm sure a lot of you knew that, right? Yes. Trees produce oxygen. I remember that from grade school. But taking a deeper dive into the biology and chemistry of it, not to mention figuring out what each of its individual cells do well, it just took on a whole new meaning for me at least. Okay, so why does any of this matter beyond the obvious plants exist and that's nice for them because chloroplast didn't just feed plants. They feed everything. Here's the timeline of how things. Went and will go cyanobacteria fill the atmosphere with oxygen. That oxygen makes aerobic respiration possible. More energy to make bigger cells eukaryotic cells develop and get complicated and get a jump on energy by engulfing mitochondria. Then another one of those eukaryotic cells engulfs a Sano bacterium, and that leads to photosynthesis. That cell becomes the ancestor of every plant and every algae that has ever existed. Plants and algae spread. They colonize the oceans. They eventually crawl onto land. They cover the continents, and they start producing oxygen and glucose at a scale the planet has never seen before. And suddenly there is food everywhere for everyone. Every animal that has ever lived has eaten either plants or something that ate plants or something that ate something that ate. Plants trace any food chain back far enough and it ends at a chloroplast, capturing a photon and using it to build a sugar molecule. You had breakfast this morning, whatever it was, eggs. The chicken ate grain toast. Wheat, a plant coffee, a plant, orange juice, a plant trace every single calorie back through the chain, and at the very beginning of every single one is a chloroplast doing its job. You are right now running on energy that was originally captured from sunlight by a chloroplast. Maybe one step removed, maybe several steps removed, but it always leads back there. So here's an, a little additional fun side off that I wanted to. Clue you in on. So we've established that animals don't have chloroplast. We never got lucky enough to make that merger stick the way plants did. We eat food instead of making it from sunlight. Fine. We made our peace with it, right? But some animals, well, they looked at plants and they were like, no, no, I want that. There is a sea slug called. Alicia Tika and this tiny little sea slug has figured out how to steal chloroplast From the algae. It eats and keeps them functional inside its own cells. This sea slug can photosynthesize. It eats alga. Keeps the chloroplast instead of digesting them and then runs them like little solar panels inside its own body. It turns green, it goes and sits in the sun, and it produces energy from sunlight for months. It is part animal. Part plant and it is doing something. Evolution spent hundreds of millions of years setting up in plants and it just borrowed it without the billion year merger, without the DNA transfer, without any of the elaborate integration. It just kept the chloroplast and put them to work, now it's not a permanent. Heritable merger. The way plant chloroplasts are, the sea slugs offspring don't get chloroplast automatically. Each new slug has to steal fresh ones from algae, so it's more of like a borrowing situation than a full endo symbiosis. But you know, still the fact that it works is extraordinary. The chloroplasts just keep running inside an animal cell, doing their job, making sugar from sunlight in something that has no business. Being able to photosynthesize and it, you know, it makes you wonder if evolution had gone slightly differently somewhere along the line, if the right eukaryotic cell had engulf. The right Sano bacterium at the right moment and kept going. Maybe animals would have had a completely different direction. Maybe we'd be sitting outside, not for warmth, but for the calories. Okay, and I wanna come back to something before we wrap up because I don't think it gets enough appreciation. Plants are genuinely extraordinary organisms that get wildly underestimated because they don't move and they don't make noise, and they don't do anything dramatic enough to get our attention most of the time. But every single plant cell is running two completely separate former bacterial organism simultaneously. Mitochondria making a TP from glucose. Chloroplast making glucose from sunlight. Two different genomes, two different reproductive systems, two different evolutionary histories, all integrated into one seamless operation inside a single cell, and they do this. In every cell of every leaf, of every blade of grass, of every tree, of every piece of algae floating in the ocean simultaneously, continuously without stopping. They are the foundation of almost every ecosystem that exists the base of almost every food chain, the source of almost every calorie consumed by almost every living thing on earth. But let's zoom back. In, pick up a blade of grass, hold it up. Now use your special microscopic vision, or just put it under a microscope like a normal person, I suppose, and zoom into one cell, one cell out of the thousands, packed into that tiny blade. And that's where we are in our story because as much as I love zooming out and describing how all of this shapes life today. We are still on our journey. We are still roughly 1 billion years ago. Everything is still single celled, still working alone, still figuring out what comes next. We are in the process of building toward complex life, one cell at a time. And we are not done yet. So in conclusion, here we are, episode seven. Cyanobacteria filled the world with oxygen and nearly destroyed everything. Episode eight, A cell eats a bacterium, it doesn't digest it, and mitochondria are born. Episode nine. This one, a cell eats a Sano. Bacterium doesn't digest it, and suddenly the whole planet has a food supply. Three episodes, three accidents. The foundation of all complex life on earth. Your mitochondria came from one ancient merger. Every meal you've ever eaten, traces back to another. You are powered by ancient accidents, plural. The chain of improbable events that had to happen exactly right and exactly wrong to get you here is genuinely staggering. Next episode, we're going inside the cell itself, the full tour. What's in there? How it's organized and what all the different parts do. The cytoskeleton, the internal skeleton that can move and reshape itself in real time, and the tiny motor proteins that literally walk along tracks inside your cell carrying cargo, like microscopic delivery drivers. I can't wait. And just a quick note before we go. When I talked about photosynthesis leading to movement versus being stationary, that was a general trend, not a rule. Not all organisms that do photosynthesis are stationary. Algae can actually move, and not all organisms that don't do photosynthesis are mobile fungus, mushrooms, mold. They just sit there and kind of liquefy the world around them and that becomes their food and some produce. Barely move at all. They hang out in the water absorbing nutrients and grabbing whatever drifts by. So when I said motion versus stationary, that was a generality, a useful one, but not a universal rule, because biology loves. An exception. Every time you think you found a clean rule, something is out there quietly breaking it, which honestly is kind of the fun part of biology, right? Sometimes the exception to the rules are the most exciting. Also, I wanna apologize for the lateness of the episode. Again, I'll get back on track for Mondays. I. And, uh, thank you for joining me on this biological journey. I'm Jackie Mullins, and this has been from Cells to us. How I'll see you next time.