Biogeochemical Cycling

Hi. It's Mr. Andersen and in this podcast I'm going to talk about biogeochemical cycles. Now that's quite a mouthful. So if we break that down that's life, earth, chemical cycling. So basically it's how chemicals move from living things to non-living things and then back again. And so up here I've written this, which is just a nemonic device to remember that atoms that life needs to survive. CHNOPS. It's carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. And so before we actually talk about cycling let's talk about why we actually need these atoms. And we're going to start with carbon. And try to be ahead of me. In other words before I flip the slide you should be planning ahead why do we need carbon. Why do we need hydrogen. So let's go to carbon. So why do we need carbon? Well carbon remember has four valence electrons. So it's really good at bonding. And so it's good at making complex organic material. And so basically if you're thinking of a protein or lipids or carbohydrates or nucleic acids like DNA, all of these things are built out of carbon. And that's because carbon is incredibly good at building upon itself. If we go to the next one, why is hydrogen important? Hydrogen is important because it makes up water. And water in general is important just because of its solubility. And it can provide a medium where life can exist. But it also can provide energy. And so if we look here, this is the light dependent reaction in photosynthesis. And you can see these protons as they flow through ATP synthase are actually making energy in the form of ATP. And so hydrogen is important just through water but also energy transfer. So be thinking ahead, why do we need nitrogen? Well nitrogen we need for a couple of reasons. This right here is an amino acid. And remember, DNA contains the blueprint to make life, but it's the proteins that actually make us the way we are. And this right here is an amino acid. All amino acids are going to have a carbon in the middle and a hydrogen attached to that. They're then going to have an amino group on one side and a carboxyl on the other side. And then an R group. That's going to be the difference in every amino acid. But this nitrogen right here is required to make amino acids or to build proteins. And so we need that nitrogen to survive. This over here is guanine. Where's guanine found? Well when you're talking about DNA what's in the middle, in other words what stores the information are the nitrogenous bases. Guanine is just one. But we also have cytosine, thymine and adenine. And so guanine if you look here has a whole bunch of nitrogen in it. And that nitrogen we have to get from our atmosphere just to make the genetic material. Let's go to the next one. Oxygen. Why do we need oxygen? Well water of course we need oxygen for. But I also included cellular respiration here. Because way at the end of cellular respiration oxygen in receiving those electrons. And so we can get a huge amount of energy as those electrons fall to oxygen. Likewise when we pull them away in photosynthesis we can store a lot of energy. If we go to the next one, phosphorus, why do we need phosphorus? Well we need phosphorus for a few reasons. Number one, this would be a phospholipid. That makes up our lipid bilayers and is going to have a phosphate in its head. If we look on the DNA right here. On the DNA we're going to have remember sugar, phosphate, sugar, phosphate, sugar, phosphate backbone. And so phosphorus is important in making our nuclear material. And the one thing that I should have included on here is ATP. And remember ATP is adenosine triphosphate. And as we attach that last phosphate on we're storing energy. Likewise we can release energy as we let it go. One of the hardest ones here is sulfur. Why do we need sulfur? Well if you look right here I've got two amino acids. This is cystine and methionine. So we just learned what an amino acid is. Again it's going to have its carboxyl group here. It's going to have its amino group, its carbon and its hydrogen. But you can see in both of these amino acids we're going to have sulfur. And why is sulfur important? Well remember proteins make us the way we are. And they have this complex three dimensional shape. And basically if you have a sulfur and a sulfur and two R groups, they'll be held together with a bond. And this is called a disulfide bridge or a disulfide bond. And so sulfur is important because it gives us structure to those big proteins. And so CHNOPS is a good way to remember all the things that we need. And again we need them for various reasons. And so we have to get them from our environment because if you think about energy, how does energy get from the sun to the earth? It just travels as light. Once it gets to the earth it's eventually used but it also eventually ends up being given off as something called heat. And so the way the energy gets to our planet is one direction. It's going to move in one direction. Then it eventually ends up as heat. But the nutrients on our planet are different. The nutrients on our planet are going to be recycled. In other words the amount of water that we have on our planet is static. The amount of carbon that we have is static. And it has to be recycled over and over and over again on biosphere, which is the earth. And they tried to do this in the Arizona desert where they built this, which is Biosphere II. They tried to keep all of the nutrients inside this biosphere that they needed to survive. They let light in, but they tried to recycle the nutrients. It worked okay. They didn't really get a good balance and so they had to open it up occasionally. And so there are cycles by which we can return that from life to non-life and then back again. Remember what we're talking about is biogeochemical cycling. How do we go from living to non-living. And so on the next four slides what I want you to think about is with each of these cycles, from the water to the carbon to the nitrogen to the phosphorus, where is most of that nutrient stored? How does it get into plants? And then how does in get into animals? And then how does it get back again. So let's start one with one that we all know. So the water cycle. So where is most of the water stored on our planet? It's going to be stored in the ocean. And so that's going to be the reservoir. That's going to be where most of the water is. How does it get into plants? Let's start there. Well there's evaporation, condensation, precipitation. But eventually we have to get it into the plants. And it's going to move into the plants through their roots. They're going to absorb that water. And it's going to move up through the xylem. So that's how it get into plants. How does it get into animals? Well we get water in us by drinking it. Or eating plants that contain water. How do we lose it? In other words how does it go back to the reservoir again? Well if it's plants we're going to transpire. They're going to lose that water through their leaves. And in us just sweat or urination we're going to lose that water back to the environment so it can be recycled again. And so the water in a water bottle used to be water in an ocean. Used to be water in a plant. Used to be water in a swamp. It's just recycled over and over and over again. So that's the water cycle. Let's go to the next one. That's the carbon cycle. Where does most of the carbon stored on our planet? It's actually stored in atmosphere. So how do we get that into plants? We get that into plants through photosynthesis. Again they're going to absorb carbon through their stomata and make sugar out of it. Okay. So how do we get it back to the environment? Well, how do we get carbon? We're going to eat plants or we're going to eat things that eat plants. And so that's how we get carbon inside us. But how do we then return it back into the atmosphere? We're going to do that through respiration. And so as we respire, we're going to return that. As plants respire, remember they're doing respiration as well, that returns it. Now one thing that we're changing the amount of carbon because we're burning fossil fuels which releases more carbon than normally would be in the atmosphere. But we've got this wonderful recycling of carbon. And why do we need carbon? Again, to build us. Let's go to the next one. That's nitrogen. Why do we need nitrogen? Remember amino acids and also the nitrogenous bases. Now the nitrogen cycle, basically how do we move that into plants? On the nitrogen cycle, on both sides we need bacteria. And so in order to get it into plants, that nitrogen in the atmosphere, it's just nitrogen gas, 70% of what you are breathing now is nitrogen. In order to get that into plants there are going to be bacteria. And basically what they're going to do is fix the nitrogen. They're going to make it usable. And so before a plant can absorb the nitrogen, it has to be fixed. It has to be converted into nitrate. And so basically bacteria are doing that. And some plants will form a symbiotic relationship where they let bacteria live on their roots as in these root nodules so they can convert it to plants. Once the nitrogen is in plants, how does it get into animals? Well they eat the plants. And we eat the animals that eat the plants. And that's how it gets into humans. But eventually we have to return it again to the atmosphere. How does that occur? We're going to have bacteria. And those bacteria as we decompose dead and dying material, those bacteria are going to convert that back into atmospheric nitrogen. And so on either side of the nitrogen cycle remember we have bacteria. And if there's no bacteria on either side we can't recycle that nitrogen. Let's go to the last one. The last one is going to be the phosphorus cycle. Phosphorus cycle, it's not going to be stored in the atmosphere this time, like it is for nitrogen and carbon. It's going to be stored in the rock. So we're going to have that phosphorus in the rock. How does that get into plants? Well there's going to be rain. And that weathering is going to break that rock down into something called soil. It's then going to be assimilated. In other words that phosphorus is going to be absorbed through plant roots so they can make things like nucleic material or ATP. How do animals get it? Well they're going to feed on that. So they're going to bring the phosphorus into them from the plants. How do we return it to the soil? Well, as we die and we decompose, that phosphorus is going to be returned to the soil. And then that soil eventually is going to become rock again through the rock cycle. And so we can return it to rock. And so it can be recycled over and over and over again. There's also a sulfur cycle as well. And so these are all biogeochemical cycles. They are ways that we can take the nutrients that we need, move them out of our environment, into us and back again. And I hope that's helpful.