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  • 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.

Hi. It's Mr. Andersen and welcome to Biology Essentials Video 13. This is on

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B2 中上級

光合成と呼吸 (Photosynthesis and Respiration)

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    Cheng-Hong Liu に公開 2021 年 01 月 14 日
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