Hi. In this video, we'll be taking a look at prokaryotic metabolism, as well as how prokaryotes factor into the ecosystem. Now, you might recall that prokaryotes have a diverse array of metabolic options. And just to review all the different terms that can apply to metabolism, let's take a look at these terms here. Now to be clear, these first two terms, heterotroph and autotroph. Right? These two terms essentially, specify where the carbon source comes from for the organism. Right? Autotrophs will make their own carbon compounds. Right? They're going to oxidize, like we learned about the Calvin cycle, for example, and they're going to use inorganic carbon, right, like CO2, CH4, these are both gases. They're going to take carbon from those gases and they're going to synthesize carbon compounds to use as fuel for various metabolic pathways. Heterotrophs, on the other hand, use carbon compounds that are synthesized by other organisms to fuel their metabolic processes. So essentially, heterotrophs all depend on autotrophs to build the carbon compounds that they're going to end up using. So again, autotroph and heterotroph simply refer to where the carbon source is coming from for these organisms. Now these next three terms, phototroph, chemoorganotroph, and chemolithotroph, these terms refer to the energy source that the organism is going to use in order to perform its metabolic functions. So, essentially, what we have here is carbon source and energy source. And we're actually going to have to combine these terms to give the full name to the metabolic pathways of a particular organism. But before I get ahead of myself there, let's talk about what each of these terms means. So phototrophs, use light energy and they're going to produce ATP via photophosphorylation, which is a process we've already talked about, back when we were discussing, photosynthesis. Now chemoorganotrophs are going to oxidize organic molecules for energy, and some are going to produce ATP via oxidative phosphorylation, which is again another process that we talked about during our discussion of cellular respiration. Lastly, chemolithotrophs oxidize inorganic molecules for energy. And, again, ATP is going to be produced by oxidative phosphorylation there. So, essentially, the difference between chemoorganotrophs and chemolithotrophs, whether or not they're using organic or inorganic molecules, and phototrophs, they are using light, not molecules, as their energy source. So you can have photoautotrophs, but you can also have photoheterotrophs. Likewise, you can have chemoorganoautotrophs or chemoorganoheterotrophs. So, essentially, you know, will pick heterotroph or autotroph, and then, one of the three below, mush them together and there you have your type of metabolism. So there are many different combinations. Right? And the basic breakdown is where are you getting your carbon from, where are you getting your energy from? Right? Those are the distinguishing factors. And, you can see that in this little diagram, many different organisms are heterotrophs. Many different organisms are autotrophs, and they actually feed into each other. You know, autotrophs provide the carbon compounds that heterotrophs are going to need to use. Heterotrophs are going to provide the inorganic materials that autotrophs will need to use like carbon dioxide. Hopefully, this is all familiar territory as these are ideas that we have discussed previously. For example, when we talked about photosynthesis. Now, the other distinctions that you need to be aware of in terms of metabolic pathways and prokaryotes involve the use of oxygen. So, some prokaryotes, eukaryotes, but we're really just worried about prokaryotes here, but some prokaryotes must use oxygen as part of cellular respiration. Right? They are obligated to use oxygen, so we call them obligate aerobes. Right? They have to use oxygen. So, this little test tube right here is supposed to represent our obligate aerobes. And the reason for that is notice that all of our cells are gathered right at the surface here, right near the air-liquid interface. So right near where the oxygen is. So they're going to be able to use that oxygen in their metabolic pathways. On the other hand, some organisms are obligate anaerobes. Oxygen is actually toxic to these species. They don't use oxygen for cellular respiration. And here is our example of those obligate anaerobes. And you can see that they are growing at the bottom of our test tube, right? As far away from the oxygen as they can get. Right? They want to be as far from that oxygen as possible because it is toxic to them. Now, we also will see organisms which we'll call facultative anaerobes, and basically these organisms can perform cellular respiration with or without oxygen. That's what we have going on here. These cells in these in this test tube all the way on the right here are facultative anaerobes. And you can see that they're pretty evenly distributed throughout the entirety of the test tube. Right? And that's because they can grow near the oxygen, they can grow far away from the oxygen, it doesn't matter. They have options when it comes to cellular respiration. They're not obligated to do anything. Lastly, some organisms will actually not perform cellular respiration at all. Right? They're not going to do electron transport. They're not going to do oxidative phosphorylation to generate ATP. Instead, they're going to rely on glycolysis. Right? Glycolytic pathways. Simply rely on the breakdown of carbon molecules and you might recall that these get that get used up in glycolysis. And this is going to allow for continued ATP production. Now you might recall that there are two types of fermentation we talked about. We talked about alcohol fermentation, which is obviously the most important type of fermentation, of course. I mean, just, duh. But then, we also, talked about lactic acid fermentation, which is actually the type of fermentation that we do in our bodies. So sorry, hate to break it to you, but you can't get drunk from making your cells do a lot of fermentation. Now looking at these different types of metabolic options, hopefully, you can see that prokaryotes really cover a very diverse range of metabolic pathways. They do a lot of different things. And that kinda gets back to the point that I've been trying to make that these are super important organisms. And actually, we're going to turn the page right now and just talk about, you know, just how important these organisms are to the ecosystem. In fact, the biosphere, life on earth, truly depends on prokaryotes to continue functioning properly, both at the level of individual organisms, but really, more importantly, for the biosphere as a whole to function properly, we need these prokaryotes. So let's flip the page and find out how that works.