In this video, we're going to take a look at energy transformations and how a cell goes about using energy. So, we've already established that the activities of the cell require energy um to function and that's one of the definitions of cell theory. So, this energy needs to come from somewhere. Lots of different processes require energy. Um so movement of the cell, metabolism, reproduction, transporting molecules, breaking down molecules, um just sort of maintaining that um internal environment within the cell membrane and a whole lot more. So lots of different processes need energy. Energy itself though is a surprisingly difficult concept to uh define. Um so as the year 11 physics teacher um even I wouldn't be able to give you a a perfect definition for what is energy but the best way we consider energy um by definition is the ability to do work. So when we say a cell has energy it's got the ability to do work and work is just those processes we discussed before. Where the energy comes from in the cell depends on its cell type. So it can either come from chemicals or from the light from the sun. Um at the end of the day though the organisms both have that access to that same sort of energy. So if an organism needs to consume that energy via food, we refer to them as what's called a heterroofe. They rely on other organisms to gain that food. And if they gain that energy from the sun, we call them an autoro. So an auto tro will get its energy from the sun. Um heterotroes can't produce all the compounds they need for their survival too. So um heterotroes are totally reliant on another organism um and consuming that organism for the energy. Um there's lots of other compounds that come from the consuming other organisms too. So they're also reliant on that regard outside of energy. Autoro on the other hand can pretty much get everything they need from the sun. So they don't actually need to they're completely self-reliant in that regard. So we'll start with autoro and autoro get their energy through photosynthesis. So you can see this equation on the board here. We have carbon dioxide and water that combines in the presence of light into um a sugar. So in this case here it's glucose and oxygen. Now, one thing I will point out that's a bit different from year 11 is in year 12, you are required to know the chemical equation. So, that equation there is something you will need to remember. Um, the easiest way and the way I recommend remembering this is to look for that number six. So, it's 6 CO2 6 H2O. The sugar's got six carbons and then it's got the same number of oxygen and double the hydrogen. So, C6 H1206. Say that a few times and you'll remember it and you get 602. Okay, so that number six is really prevalent. It's prevalent in all the molecules. Um what photosynthesis does is it converts basically light energy into a form of chemical energy in that sugar. But what's really important to note is that photosynthesis doesn't actually create energy itself. In fact, it actually uses energy. What photosynthesis does is it creates glucose or creates a sugar that can be then be used for energy. So that's where one thing that pretty much every cell type has in common is aerobic respiration. Um so aerobic respiration is basically the reverse process where we take the glucose and we break it down to produce energy. So where autoroes and heterotroes differ primarily is the fact that this glucose in an auto tro comes from photosynthesis. But in a heterotroof, this glucose comes from another organism, whether that's a plant, an animal, whatever. Um, you'll notice that the reaction is essentially the reverse. So now we're going, we have glucose plus six oxygen produces six carbon dioxide and six water molecules. And you also get energy coming out of that. So I'll come back to ATP shortly, but this is kind of how the cell stores energy. It stores it in the form of this molecule here. Okay? But this is an energy producing pathway. So in aerobic respiration the energy comes out the end of the reaction whereas um in photosynthesis it comes in from sunlight. So if there's no oxygen um it probably stands to reason then the cell's dead. If we go back and have a look you can see that oxygen is pretty important. Um however interestingly enough not every cell requires oxygen. there's actually a whole branch of cells particularly um some of the bacteria that live in your digestive tract for example that don't actually require oxygen to live. So they can switch to a different process. Um and this process is fermentation. So fermentation is what we call an anorobic process. It's an anorobic alternative to aerobic respiration or anorobic respiration. Um anorobic basically means without oxygen. So it doesn't require that oxygen to generate the energy from glucose. Fermentation's a little bit more complicated. Um not so much in terms of the process, but in the fact that there's actually different types of fermentation. So you can see here that in yeast, plants and some bacteria cells, I would say most bacteria cells, um it actually we get this process here. So glucose is the same molecule as before, breaks down to form ethanol. and two carbon dioxide molecules. So again, you do need to know the chemical equation here. This one's a little bit more complex. Um the rule of six doesn't really apply here, unfortunately. This one is probably one you're just going to have to keep practicing and keep, you know, using flash cards and that sort of thing to help remember. Um so what happens is ethanol glucose breaks down and forms two ephanol molecules. So, ephanol is C2 H5OH. It's got a bit of a weird um formula. I'm not quite sure why they set it out this way, but that's what it is. And you get two carbon dioxide molecules. So, where you'd probably know this um or where this is most familiar is in things like baking. So, when we put yeast into a cake or bread, um this reaction is happening. And so, what happens is the the yeast um produce carbon dioxide and that causes your bread to get all sort of fluffy. Alternative alternatively though, this ethanol can also be quite useful. So we use ethanol in things like beer brewing and it's essentially alcohol really. So wine, beer, spirits um all take advantage of this process and usually involve yeast. Um on the other hand in animal cells um it's a more simplified process. So rather than getting ethanol and carbon dioxide, animal cells will take glucose and turn it into lactic acid. So lactic acid's probably best known. You might hear your PE teacher talk about when your muscles get sore, it's because there's a buildup of lactic acid. It's not actually true, but um that's that's kind of where it's well known. So it builds up in your tissues. Um, human cells can use this lactic acid um to produce energy and typically we do this for really um short bursts or really high intensity energy um consumption because what what effectively happens is our cells can't sorry our body can't provide enough oxygen to our cells. So when there's not enough oxygen getting there, the cell reverts to this fermentation. So when we start sprinting, you can usually sprint off really quickly, but then inevitably you're going to get tired. So if we can survive without oxygen um obviously we can't survive without oxygen but clearly ourselves can. So what's going on here? Reason for this is to do with the amount of energy they actually get out of the process. So aerobic respiration is actually very efficient. Um you can see here think of these ATP molecules I'll talk about them in a moment. Think of them as like units of energy. So what happens in aerobic respiration is we get um we get a number of ATP molecules or ATP energy units I guess being produced around 30 to 32. Compare that with fermentation you can see that only produces two each. So aerobic respiration actually produces 16 times more energy than fermentation. And that's the reason why our bodies or why us as organisms can't actually survive um without oxygen is because simply this process doesn't produce enough energy. So, this is useful when you need a really short burst of energy. Um, and hence why you can probably sprint for about 10 seconds at full speed and then after that you get very tired pretty quickly. So, we're going to talk about ATP now which is a little bit more complicated. Um, basically cells in order to use that energy we talked about before need to use this idea of energy coupling. So what they have to do is because energy itself isn't like a substance or a material um we need to be able to move energy from one place to another. So if you think about this um in everyday life, think of it kind of like electricity. Um electricity is energy. So the way we move electricity around is we have you know things like wires and batteries. ATP in your cell is essentially the the battery of your cell. So what happens is um when we go through respiration or fermentation and produce that energy your cell will take the energy and couple it to a molecule and that molecule is ATP. So ATP is effectively like a little battery. When it's in the form ATP it's charged up and then it can move energy to different parts of the cell. So ATP is the fully charged battery version and you can see it up the top here where my mouse is. So we have an adinine, a ribos, and then we've got these three phosphate groups. Now, most of this molecule doesn't really matter too much um for what we're interested in, but this part here is really important. So this last chemical bond, so you can see we got these phosphates joined together and there's an oxygen between them all. And then we got this third one right at the very end. We've got one particular bond here. This is what we call a high energy bond. So you need a lot of energy to make this chemical um happen essentially. So when we're breaking down energy in our cells, the energy from the glucose and from aerobic respirations actually used to basically make this chemical reaction happen. Okay? And the cell will insert that energy into this chemical bond. Okay? When this chemical bond breaks, that's what releases the energy to the different parts of your cell. So aerobic respiration will happen. it'll put the energy into this molecule in the form of this chemical bond. The ATP will then go out into the cell where it's needed and then once the ATP finds a a particular place or reaction that it's required for, um, the cell will do what's called a process called ATP hydrarolysis. This is where ATP is reacted with a water molecule. And what that water molecule does is it helps to break that chemical bond. So what will happen is ATP will hydrarolysis will happen where the energy is required. The um what will happen is the water molecule will basically shear off that chemical bond and you can see here we get this phosphate group formed and then you can see that we got this shortened molecule and this process releases that energy for where it's required. So in ATP hydraysis the ATP is broken down into another molecule called ADP. So if ATP is adenazine triphosphate, ADP is adenazine diphosphate diam meaning 2. Okay. So ATP hydraysis is the process that releases the energy by reacting with water. On the flip side though, um this battery system, they're kind of like rechargeable. So ATP hydraysis releases the energy and then when we want to put the energy back in, we can actually take this ADP molecule and we can take the energy from respiration to basically charge that battery back up again. So this is called ATP synthesis. In ATP synthesis, what happens is the ADP molecule will react with a phosphate group um with the energy from uh respiration or fermentation to put that phosphate back on and effectively recharge the battery. So, it's kind of like a cycle. So, these are the reactions here. We got hydrarolysis and synthesis. ATP will react uh will break down to form ADP a phosphate or the the I on the phosphate stands for inorganic phosphate. You don't need to worry too much about that and that produces energy. ATP synthesis on the other hand is the reverse. So we're taking the energy putting it into the ATP molecule. So ATP is used to power pretty much all the activities of the cell. It's what we call the cell's energy currency. So your cell can't really use energy unless it's in the form of ATP. This energy is really important because your cell is effectively just an organized bag of chemical reactions. And so those chemical reactions need that activation energy we talked about in the previous topic to happen. And so the ATP is really providing that energy to the cell. This picture on here, not there there to frighten you, is just to so you can see the scale of all the different reactions that happen in your cell every day. And this is unfortunately this isn't actually all of them. This is just to do with energy use. So the the reactions that I'm talking about here are very very simplified. They are in reality a lot more complicated. And if you go on to do um biochemistry at uni, this is some of the stuff that you end up looking at. Um it's a very complicated process but um ATP is essentially the energy that drives all these reactions to happening.