Hi, in this video we'll talk about biogeochemical cycles, which are related to life on Earth, and chemical cycles. These cycles explain how chemicals move from living things to non-living things and back again. Look up here, I've put this mnemonic to help you remember the atoms that life needs to survive: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. But before we talk about the cycles, let's see why we need these elements. Try to think ahead of me, though. Let's start with carbon. Why do we need carbon? Well, remember that carbon has four valence electrons. It's very good at forming bonds and can form complex organic materials. So, if we think about proteins, lipids, carbohydrates, or nucleic acids like DNA, all of these are built with carbon. That's because carbon is very good at forming something with itself. Okay, now let's see why hydrogen is important. Well, hydrogen is important because it can form water, and water is very important for many reasons, but above all because life can exist with water due to its ability to act as a solvent and to provide... A medium in which life can exist, but it can also provide energy. For example, this is a reaction from the light-dependent reactions of photosynthesis. Notice these protons moving through ATP synthase, generating energy in the form of ATP. So hydrogen is important not only for water but also for energy transfer. Now let's look at oxygen. Why is it so important? Well, we need oxygen to form water, but it's also very important in cellular respiration. Look, in the end, oxygen receives electrons, and we can generate a large amount of energy as those electrons leave with the oxygen. Likewise, when we remove them in photosynthesis, a lot of energy can be stored. Now, you might be thinking, "Why do we need nitrogen?" Look, we need nitrogen for a couple of things. Here we have an amino acid, and remember that DNA contains the information to create life. But thanks to proteins, we are who we are. So, this is an amino acid, and all amino acids have a carbon in the center bonded to a hydrogen atom. Then we have an amino group on one side and a carbon- binding group on the other. And then we have an R group, which is what gives it... It gives each amino acid its unique character, but look, this nitrogen is very important for forming amino acids or proteins. That's why we need nitrogen to survive. And here we have guanine. Where do we find guanine? Well, if we're talking about DNA, the nitrogenous bases are responsible for storing the information. Guanine is one of them, but we also have cytosine, thymine, and adenine. So, in guanine, there's a lot of nitrogen. We need nitrogen from the atmosphere to form the genetic material. Now let's look at phosphorus. What do we need phosphorus for? Well, we need phosphorus for several things. Here we have phospholipids that form the lipid bilayers, and here we have a phosphate group. If we analyze DNA, remember that in DNA we have sugar phosphate, sugar phosphate, sugar phosphate. So, phosphorus is very important in the formation of our genetic material. And something I didn't mention but that is also important is ATP. Remember that ATP is adenosine triphosphate. So, with this factor, when we attach the third phosphate, we can store energy, or we can release energy when we let it go. And finally, let's look at the Sulfur is more difficult. Why do we need sulfur? Well, here I've put two amino acids, cysteine ​​and methionine. We've already learned that an amino acid consists of a carbon group, an amino group, a carbon atom, and a hydrogen atom. But we can see that both amino acids contain sulfur, and sulfur is very important because, well, remember that proteins are what make us who we are, and they have a very complex three-dimensional shape. So, if we have a sulfur atom and a sulfur atom with two Cr groups, a bond is formed like the one we have here. This is known as a disulfide bridge or disulfide bond. So, sulfur is important because it gives structure to large proteins. That's why CHAMPS is a good way to remember all the elements we need. We've already seen that we need them for different things, so we need to obtain them from our environment. Look, if we think about how energy travels from the sun to the earth, we know that it travels in the form of light, but once it reaches the earth, it also becomes heat. So, for energy to reach our planet, it moves in one direction and is converted into heat. But with the nutrients on our planet, it's different because nutrients are recycled. For example... The amount of water we have on our planet is static, the amount of carbon is static, and they are recycled over and over again in the Earth's biosphere. In fact, they tried to do that in the Arizona desert. They built this and called it Biosphere 2. They tried to keep all the nutrients needed to survive inside this biosphere, which allows light to enter. They tried to recycle the nutrients, and it worked well, but they didn't really achieve a good balance, so from time to time they have to open it. And well, remember that we are talking about biogeochemical cycles, how nutrients pass from living things to non-living things. Well, I will show you four images of each cycle: the water, carbon, nitrogen, and phosphorus cycles. But I would like you to think about where most of these nutrients are stored on our planet and how they reach plants and animals and how they return to the environment. Let 's start with a cycle we all know: the water cycle. Now, where is the largest amount of water stored on our planet? Of course, it's in the ocean. That's our reservoir. And how does it reach plants? Well, through evaporation, condensation, and... Precipitation eventually reaches plants through their roots, which absorb the water. That's how it gets to plants and animals. Well, water reaches us by transpiring or eating plants that contain water. And how do we lose it, that is, how does it return to its source? Well, as you know, plants transpire, losing water through their leaves, and we lose it through sweat or urination. This way, the water returns to the environment to be recycled again. So, the water we keep in a bottle was once in the ocean, in a plant, in a lake, and so it is recycled over and over again. That's the water cycle. Now let's look at the carbon cycle. We'll see that most of the carbon that exists on our planet is stored in the atmosphere, but how does it get to plants? Well, it gets to plants through photosynthesis because, remember, plants absorb carbon through their roots and use it to produce sugars. Okay, and how does it return to the environment, or how does it reach us? Well, we eat plants or animals that eat plants, and that's how carbon gets into our bodies. But how do we return it to the environment? Well, through respiration, if we breathe, we return carbon to the environment, just like plants do because remember they also respire; it's just a matter of returning it. But one thing that changes the amount of carbon is the burning of fossil fuels. That releases more carbon than is naturally present in the atmosphere. But fortunately, we have this wonderful carbon recycling system. And why do we need carbon? To build ourselves, okay? And now let's look at the nitrogen cycle. Why do we need nitrogen? Well, remember, for amino acids and nitrogenous bases. Now, in the nitrogen cycle, we need bacteria on both sides. So, for nitrogen to reach plants, it all starts with gaseous nitrogen in the atmosphere. Remember that 70% of what we breathe is nitrogen, and for it to reach plants, bacteria are needed. What they do is fix nitrogen. So, before the plant can absorb nitrogen, it has to be fixed, it has to be converted into nitrate, and that's what bacteria do. Some plants even form a symbiotic relationship with bacteria, allowing them to live in their roots, as in this image. But once nitrogen is in the plants, how does it get to the... Animals, well, animals eat plants, and we eat the animals that eat plants, but at some point, we have to return it to the atmosphere. How does that happen? Well, again, we have bacteria that, through the decomposition of matter, help return nitrogen to the atmosphere. So, on both sides of the nitrogen cycle, bacteria are needed to recycle nitrogen. And finally, let's look at the phosphorus cycle. In this case, phosphorus isn't stored in the atmosphere as happens with nitrogen and carbon; rather, phosphorus is stored in rocks. How does it get to plants? Well, when it rains, the water erodes the rock and carries it to the soil where it is assimilated. That is, phosphorus is absorbed through the roots of plants, and that's how they can produce things like their genetic material or ATP. How do animals get it? Well, when they feed on plants, they carry phosphorus to themselves. How do they return it to the soil? Well, when a living thing dies and decomposes, it releases phosphorus, and over time, the soil transforms, and the phosphorus returns to the rock. That's how phosphorus is recycled again and again. So, these are the cycles. Biogeochemicals are the processes by which we obtain nutrients; we take them from the environment and we also return them. I hope this is helpful.