字幕列表 影片播放 列印英文字幕 Hi. It's Mr. Andersen and welcome to Biology Essentials Video 13. This is on free energy capture and storage. But what you'll quickly learn is that this is mostly about photosynthesis. And this is actually a map of photosynthesis on our planet. So what you could see this is both on land and on the ocean, you'll see that photosynthesis is going to be highest in areas like here, South America. That'd be the Amazon. Or eastern North America. Or you'd find it in a lot of northern Europe and northern Asia. And so it's mostly about photosynthesis. And we also see it in the ocean. So we're going to see a ton of it near the equator but not exactly at the equator and I imagine that has to do with the currents. The other thing it's going to be about is respiration. And so I'm going to try to get through the whole thing on photosynthesis and respiration. If it seems like I'm going too fast or it's not understandable, I've made a video on both photosynthesis and respiration individually and so take a look at those. And I hope that will be helpful. So what am I going to talk about in this. Well just like in the last podcast I'm going to talk about how life uses free energy. The goal of life is to make ATP so we can use energy. Now there's two life strategies. There's the life strategy of the autotrophs. An example would be a plant. Those are things that make their own food. And then the heterotrophs. An example would be you. And you're a heterotroph. That means you eat your own food. And so autotrophs on our planet mostly use photosynthesis. So they take energy from the sun in both light reaction and the Calvin Cycle to make sugars, or to make macromolecules that they can use. There's an obscure group of organisms on our planet that don't have light available and it doesn't mean they are out of luck. They use chemosynthesis. So they use the energy found in chemicals to actually make their food. The other life style then is heterotrophs. Heterotrophs are going to use cellular respiration which is essentially oxygen, mitochondria, sugar and they're going to make ATP from that. It requires oxygen which pulls on those electrons. We'll talk about that in a second. And the process is glycolysis, Krebs Cycle and then finally the electron transport chain. If you don't happen to have oxygen you can also use a process called fermentation. I'll explain that. Now the thing that I really haven't talked about, oh, I'll talk about evolution as well, but the one thing that I want to make sure that you understand is that autotrophs aren't making the food for us, they're making the food for themselves. And so not only does a plant do photosynthesis, they then use cellular respiration to actually break the energy and get the energy out of the food that they ended up making. And so this kind of summarizes that cycle. So what we have are the way of the heterotrophs. They take organic molecules and oxygen and they use that to make carbon dioxide and water. We call that process cellular respiration. And then autotrophs will actually convert that back into organic molecules so they can then utilize that energy. And so most of those on our planet use photosynthesis, like plants. And most of the heterotrophs use cellular respiration. An example would be like a cheetah. But I do want to briefly talk about chemosynthesis. Chemosynthesis occurs where there's not a lot of light on our planet. Where's a great example of that? Deep dark in the ocean. And so these are giant tube worms which can get something like 21 feet long. So pretty ridiculous. But these tube worms actually have right here this portion where they're actually taking in carbon dioxide, taking in oxygen, taking in hydrogen sulfide gas from these black smokers which is just organic materials coming out of a, situated over a hot spot. And what they're doing is feeding bacteria that live in their gut. Those bacteria that live in their gut are actually taking that hydrogen sulfide gas and they're utilizing the energy from that to make simple carbohydrates. And so they don't require light at all. They're actually making sugars using powers of the chemicals. Another example of that is what if you don't have oxygen? Well you can use a process called fermentation. And so this is how wine is made. It's a barrel that they've actually cut in half. And so these are yeast that would die because you're not letting them get any oxygen. But they can actually do alcoholic fermentation to survive until they eventually die. We use something called lactic acid fermentation to do the same thing. It's a form of energy capture but we don't require oxygen to do it. Okay, so let's talk about photosynthesis and respiration. So this is my animation for how photosynthesis works. And the one thing that you want to always . . . the problem when you're doing photosynthesis and respiration is that you get so into the steps that you don't really understand what's going on. You miss the forest for the trees. And so what we're doing in photosynthesis is taking carbon dioxide, plants take that in, taking water and converting that to glucose and eventually to oxygen. And so if I animate it, it looks like this. And so what we're doing is we're taking the carbon in carbon dioxide and we're actually turning that into carbon in glucose releasing oxygen as a waste product. But what we're really doing is we're storing energy in this glucose molecule. The delta G or the free energy is positive. That means that we're storing energy in that glucose molecule. We're actually storing it in these bonds right here between the carbon and the hydrogen. Now it's not as simple, I wish it was, it's not as simple a chemical reaction as this. It's actually pretty complex. But what I don't want you to miss is I don't want you to miss what happens to the carbon dioxide? What happens to the water and how does that convert into glucose and oxygen? And so if you miss that then I've done a bad job. Okay, whenever I'm thinking about photosynthesis I actually break it down into the two words so I can remember the different parts. The photo part is the light reaction and photo means light. And synthesis means to build and so that's going to be the Calvin Cycle. And so the photo part or the light reaction is going to take place, the whole thing of photosynthesis takes place in the chloroplasts. And here's a bunch of chloroplasts inside a plant cell, but the light reaction is going to take place right here. It's in the thylakoid membrane. And if we have a bunch of thylakoid membranes stacked up then we call that whole thing a granum. So what happens in the light reaction? We take in water, we take in light and we release oxygen and then we store that energy in ATP and NADPH. The next step is the Calvin Cycle. Calvin Cycle, where's that take place? Well that takes place in this liquid portion inside the chloroplast. That's called the stroma. And in the Calvin Cycle we're going to take the energy of ATP and NADPH and we're going to take carbon dioxide and we're actually going to make sugars out of it. And so in summary that's what photosynthesis is. It's taking in energy in the form of light and eventually storing that energy in sugars. So what is that sugar we're talking about? Glucose, like I just mentioned a second ago. Now the actual process is not that simple. And so the light reaction is where you should spend most of your time trying to figure out photosynthesis. And so where are we? We are in the thylakoid membranes, so this is going to be inside the chloroplast itself. And so what we get is light. And that light is going to come into photosystem 2 and photosystem 1. Inside here we have chlorophyll. Chlorophyll is a magical pigment that can absorb light energy and get excited and pass that excitement on in the form of electrons. And so the first thing that happens, let me change color, is that light comes in and that gets the chlorophyll excited. It also is going to pass an electron down an electron transport chain. So let's follow where that electron goes. It eventually goes to NADPH. And so that electron that goes down this electron transport chain has to come from somewhere. And so where is it coming from? It actually comes from the water. So again what is another thing that we need in the light reaction? We need water. And so the energy is coming from that, or the electron is coming from the water. That's splitting water and it's splitting water into oxygen. So oxygen remember is one of the products that we give off in photosynthesis. That's what you're breathing right now. But we also create protons. Protons are simply hydrogen atoms that have lost their electrons. And I'll get back to those in a second. So let's track those electrons again. So the electrons are flowing through an electron transport chain in the thylakoid. And as they go through these proteins, which I don't ever want you to memorize the names of, as they go through these proteins what they're doing is they're using their energy to actually pump protons to the inside of the thylakoid membrane. And so what we're doing is we're moving protons to the inside of this membrane. So we're increasing the number of protons inside here. So we're making it really positive on the inside of that thylakoid membrane. Now the protons have nowhere to go. The only way that they can go is out through another protein which is called ATP synthase. And so it uses the energy of those flowing protons to actually make our friend ATP. And so let's track what we've got. We've got light coming in. We've got water breaking down into oxygen, to give up its electrons and now we've made NADPH, that's where the electrons end up and then ATP. So we've stored the energy of that light in ATP and NADPH. Now what do we use that light to do? Well, Melvin Calvin who invented not, but discovered the Calvin Cycle shows the process that happens next. So essentially what you do is take in carbon dioxide, so plants take that in through their stomata, they then use the energy of ATP and NADPH to convert that into sugar. And so this is a G3P molecule. But essentially we can use that to make sugars inside a plant. And so all these intermediary chemicals you don't need to know. What you do need to know is that we make ATP and NADPH. So we can use the energy of that to actually make sugars. Now where does the Calvin Cycle take place? Calvin Cycle is going to take place in the stroma, the liquid portion of the cell. So that's how we store our energy in sugar. The evolution of that in our planet we think happened really early. So we think those first life forms on our planet were actually using some form of photosynthesis, maybe chemosynthesis to begin with, but we do know this. That about 2 billion years ago, when we look at the rock layer, this rock is from about 2.1 billion years ago, we start to see red showing up. And red bands showing up. And what that indicates is that oxygen is being produced at appreciable amounts. So this right here is actually a graph of atmospheric oxygen through time. So here we are today and this is for the last 3.8 billion life on our planet. We see that the amount of oxygen has increased. And these two lines here are just the guesses that scientists have. Kind of a high - low guess. And so we know that the oxygen levels on our planet have increased over time. Where did that oxygen come from? It actually came from photosynthesis. Next let's go to cellular respiration. What happen in cellular respiration? Cellular respiration we're actually using the energy in those sugars. So in glucose in the presence of oxygen we're breaking that down into carbon dioxide and water and we're releasing energy from that. So let's see what that looks like. So we break down that glucose, that's an exergonic reaction. We're releasing energy. We're making carbon dioxide. We're making water, but we're mostly making energy in the form of ATP that we can use. Again, it's not as simple as this. So let's get to what respiration really looks like and where it takes place. In order to do cellular respiration you need a mitochondria and you also need one more thing. You need O2. You need oxygen. So the parts of the mitochondria that you should become familiar with, first of all we've got an outer membrane. Outer membrane's going to be this portion right here. We also have an inner membrane. So it looks like that. We have an inner membrane space. The inner membrane space is going to be right between the outer and inner membrane. And you see here that we have these folds that go on the inside of that inner membrane. And what that does is increase the surface area. But the last thing that we should become familiar with is actually called the matrix. Matrix is going to be the inside of the mitochondria. And so the parts of cellular respiration, the first part is called glycolysis. That'll actually take place out here. Next thing is going to be the Kreb's Cycle. Kreb's Cycle will take place in here. That's in the matrix. And then finally we have the electron transport chain. Electron transport chain is going to take place along that inner membrane. And so the reason we have that fold is to increase surface area. Now this looks a little scary, the diagram but it shouldn't be that scary because we're going to miss all of the intermediates. So what do we start with, glucose and we break that down into pyruvate. One thing that you should know is that glucose is a six carbon molecule and down here, pyruvate we have 2 three carbon molecules. We release a little bit of ATP in glycolysis and that takes place outside of the mitochondria. Next we enter into the Kreb's Cycle. And in the Kreb's Cycle we're going to take that carbon which is in pyruvate and we're going to release that as carbon dioxide. But the important thing we're doing in the Kreb's Cycle is we're storing energy. We're storing energy as N-A-D-H NADH and F-A-D-H-2 or FADH2. So we're storing the energy that was found in the pyruvate in NADH and FADH2 so we can finally use that in the electron transport chain. Let's look at what happens in a little more detail as far as the electron transport chain. We've stored energy now in NADH. And we've stored energy in FADH2. We're going to transfer that energy in the form of electrons, just like in photosynthesis. We've now got an electron transport chain. It's not in the thylakoid. It's the inner membrane. But as we transfer that electron through the electron transport chain, we're pumping protons to the outside of the inner membrane. So it's now in this inner membrane space. We now have a build up of all of this positive charge here. The only place it can go is through our friend ATP synthase and we eventually make ATP. So that energy that you use right now, the energy you're using to think, to move, all of the actions, that ATP comes from that flow of those protons through here. Now the puzzle's not quite complete because we dropped off that energy of NADH and FADH2. Well, let's follow what happens to that electron. That electron is eventually going to combine with oxygen and hydrogen and we're going to make H2O. And so who's pulling that electron the whole way? Our friend oxygen. Oxygen is pulling that electron towards it. It's highly electronegative and when it finally gets to it, we've made our product. We've made H2O which is given off. But more importantly we've made ATP. And we've made energy through this process of cellular respiration. So photosynthesis and respiration are how we utilize energy, free energy from the sun to make ATP, to make ourselves grow. So I hope that's helpful.