Transcription
So the topic of this video are what are called biogeochemical cycles. And through the video, I'm eventually going to discuss the water cycle, the oxygen cycle, the carbon cycle, the phosphorus cycle, and the nitrogen cycle. But, you know, I actually have a separate video for the four I just highlighted: water, carbon, phosphorus, and nitrogen. I go a little slower in those separate videos and into a little more detail, so you also have the option to watch those videos instead of the one long video that you see right here.
But let's go ahead and get started. So the first biogeochemical cycle I want to mention is the water cycle, also known as the hydrologic cycle. And in this cycle, it's simply the movement of water through the atmosphere. Now, when you look at a picture of the, a globe of the Earth, you know, about 75% of Earth's surface is covered with water. But there's a problem with that water. Most of the water on Earth is undrinkable. It's either too salty because it's ocean water, or it's frozen like in glaciers and icebergs. So the vast majority of Earth's surface is covered in water, but it's not drinkable water. So we really need to understand how the water cycle works so we can take care of the water that we need to survive.
So let's look at the stages of the water cycle. You know, water rises into the air in two ways. One, the most obvious is evaporation. Heat from the sun causes water vapor to rise into the air. So liquid from the pond, liquid water turns into a vapor and rises into the air. A second way that water rises into the air is through what's called transpiration. Plants will lose water through their leaves. That's what transpiration is. So when we look at transpiration in a little more detail, plants have these tiny openings called stomata on their leaves. Here's a leaf, let's zoom on in, and when we do, we see it almost looks like an eyeball. We're zoomed in here, really, really high, highly magnified. This is an example of a stomata here. It's a tiny pore, microscopic, where water vapor can exit. So this is how water exits during transpiration.
So when we look at our cycle again, water is rising through evaporation and transpiration. Well, what happens is, of course, water collects in the atmosphere and eventually it's going to condense and form cloud. And so when we continue on with our hydrologic cycle, now that there's water vapor in the atmosphere, condensation occurs because as water rises into the air, it eventually encounters cooler temperatures. You know, you know, examples of condensation on a hot summer day, for instance. Let's say you take a soda out of the refrigerator and leave it outside for five minutes. After five minutes, you come back and there's these little water droplets all over, all over the the soda bottle. Well, did water leak out of the bottle? No, moisture in the air, water moisture in the air came in contact with the cold bottle and it condensed and formed these little droplets. So the same thing happens is when water vapor rises into the air, it cools and condenses and forms clouds. Clouds are the effects, the results of condensation.
And then once clouds are formed, that will lead to some form of precipitation, the falling of water back to the surface of the Earth. And when it comes to precipitation, it might be the most obvious type, such as precipitation of rain, or of course, there's the precipitation called snow, precipitation called sleet. It's kind of like it's not cold enough for snow, not warm enough for rain, you get this mixture of slushy material called sleet. By the way, sleet is really slippery to drive on for all you young drivers. So if you ever caught in a sleet storm, pull over, get some lunch, and wait the storm out. And then there's hail. Hail is the fourth type of precipitation. Little chunks of ice can fall to the ground. And when you look at this person's holding hail balls in their hand, you can imagine these things are falling from very high altitudes and they could cause bodily injury or even property damage. You see here's a broken window. The back window of this automobile has been broken out because of hail damage. So if you live in areas that constantly get hail, you may want to look into hail insurance.
And so once water is on the ground because of precipitation, one of two things will happen. Either it will run off downhill, and runoff is simply when water runs downhill into a river, into a lake, into an ocean. Or the water will soak into the soil, and that we call that infiltration. And when water soaks into the soil, it begins to collect underground in this big pool of water underground called groundwater. And that's where a lot of the world gets its drinking supply from, drinking water from, is from underground groundwater. And so when we look at this picture here, we can see that there's, um, you know, a cutaway of the earth. We can see the groundwater underneath the surface. Well, what we'll do is we'll drill wells down into that groundwater and then we can pump the water out of the ground and use it for our everyday needs. So how come, how come these underground supplies of water don't go empty? Well, that's because of infiltration. The groundwater is recharged or resupplied or restocked because of infiltration. If water didn't seep back into the groundwater, we'd run out.
So the purpose of this final slide on the water cycle is to show just a summary of the two ways that water goes up: transpiration and evaporation. Eventually, that leads to clouds condensing and forming. And when water vapor gets too heavy, it condenses and then it falls as some type of precipitation. When water hits the ground, it will either then run off downhill or it will soak into the soil as infiltration. Either way, I hope you see we have a nice cycle. And again, this is simply the hydrologic or the water cycle.
So as we now switch to the oxygen cycle, this, I don't have a specific video for the oxygen cycle because this is pretty quick and pretty basic. But the tree represents photosynthetic autotrophs, and photosynthesis requires the intake of carbon dioxide. Again, plants have those stomata, which I mentioned during the water cycle, and when the stomata are open, they can take in carbon dioxide simply from the environment, from the air. And they will use that carbon dioxide to produce their food. In the process of photosynthesis, and as a result of producing their food through photosynthesis, they will release oxygen as a waste. The oxygen simply exits through the stomata when they're open and accumulates in the atmosphere.
And then come the heterotrophs, represented by our cow. Now, again, heterotrophs can be not just animals, but let's also, let's not also forget, you know, fungus and decomposers and bacteria. And so through the process of cellular respiration, oxygen will be inhaled. Oxygen will be inhaled. The oxygen that came from photosynthetic organisms is inhaled. And cellular respiration, if you recall, is the process that where ATP, adenosine triphosphate, is made. And in order to make ATP, oxygen is one of the reactants. And so the, the cow is now exhaling carbon dioxide because carbon dioxide is a waste product of cellular respiration. And so you can see from the video here, we have a nice, pretty straightforward overall cycle where the cow gives off carbon dioxide, which is taken in by the plant. The plant gives off oxygen, which is taken in by the cow.
So when we look at the carbon cycle, I want to look at the carbon cycle next. Carbon, why do we need it? Because carbon is the basis of organic molecules. Remember the four categories of organic molecules? You got proteins. Remember, proteins are a big chain of amino acids. Foods that are high in proteins would be like fish and eggs and and steak and meat. And let's not forget another category are carbohydrates. The diagram is a diagram of glucose. You can see carbon in the diagram of glucose. Foods that are high in carbohydrates would be pastas and fruits. A third category of organic molecules would be lipids. Here we have a, an animation of the cell membrane, the phospholipid bilayer. And so the outer boundary of every cell in our body needs carbon. And then the fourth category of organic molecule, the nucleic acids, the DNA and the RNA, the genetic basis of life here on Earth. So that makes carbon really important.
Let's go ahead and go on into the stages now. So when we focus on the carbon cycle, you know, plants and producers. So you see the plant on the far right is absorbing carbon dioxide so it can use carbon dioxide as one of the reactants of photosynthesis. And through photosynthesis, this plant and other types of autotrophs will produce glucose. Remember, glucose is carbon-based, so there's carbon in glucose. And then now that the plant has made carbon, the carbon simply moves up the food chain. The plant has made carbon in the form of glucose, and the glucose simply moves up the food chain. In the animation, glucose is going to the rabbit because the rabbit's eating the plant. Glucose is going to the wolf because the wolf is eating the rabbit. Glucose simply moves up the food chain. Animals, let's not forget, do cellular respiration. And as a result, they release carbon dioxide back into the environment. So if you notice in the animation, we already have a little cycle, and we're not entirely done yet, though.
So before we finish this up, I want to mention, of course, the role of the decomposers. They're going to obtain glucose by feeding on the dead. So in the animation, glucose from a dead wolf, from a dead rabbit, from dead plants are going to the mushrooms, which represent decomposers. And decomposers also do cellular respiration, so they too release carbon dioxide into the atmosphere. So now we have a full cycle involving autotrophs, heterotrophs, and decomposers.
And so before we, uh, move on, I want to mention the human contribution. You know, excess amount of carbon dioxide has been released and burned. I should say, excess amount of carbon dioxide has been released into the atmosphere from the burning of fossil fuels like coal, oil, natural gas. So in the animation, you see a factory releasing all these extra amounts of carbon dioxide. This is leading our carbon cycle to be out of balance. And so, you know, later on, we're going to go over some of the, the details of climate change and global warming. And but, uh, for, for, for those of you who understand this topic, it's because of carbon dioxide and other greenhouse gases like methane are out of balance with the natural carbon cycle. So with our cycle being out of balance, you know, we're fearful that this could alter, you know, weather patterns around the world and, and, and disrupt some of the cycles, the natural weather cycles that we've seen for thousands of years.
So the purpose of this slide is just to show a summary of the cycle. And I hope you can see a, a clockwise cycle in my animation here. And so you can see carbon cycling and moving in a circular motion throughout the environment. Let's go ahead and go into the next cycle.
Okay, so the next cycle I want to mention is called the phosphorus cycle. And, you know, there's a problem. We need phosphorus, but there's no phosphorus in the atmosphere. And the reason we need phosphorus is because phosphorus is needed to make ATP. Here's a mitochondria picture. And if we look at the molecule ATP, you can see there's P in it for phosphorus. We also need phosphorus to make DNA, deoxyribonucleic acid. If we look at a nucleotide, we can see that there's a P in the diagram because again, one of the parts of a nucleotide is called a phosphate group. And when you combine one nucleotide with several others, you have a molecule called DNA. And another reason why we need phosphorus is because of lipids. Here's a, a picture of a cell membrane. Remember that a cell membrane is made from a phospholipid bilayer. Phospholipid because there's phosphorus in it.
So let's go ahead and get into the steps of the phosphorus cycle. So when we look at the stages of the phosphorus cycle, we see, hey, it's raining in my animation. And that's kind of one of the most important steps. This helps release phosphorus from rocks. There is no phosphorus in the atmosphere, but there's phosphorus in rocks. And when rocks are exposed to rain and changing temperatures and the cold and thawing, this helps to release phosphorus from the rocks. And now that there's phosphorus in the soil, it simply is taken up through the roots of plants and producers. And now that it's in producers, it simply moves up the food chain. And once phosphorus is absorbed through the roots of plants, phosphorus simply moves up the food chain from the plants to the snail because snails eat plants, from the snail to the frog because frogs eat snails. Phosphorus is moving up the food chain. And even to the decomposers. Decomposers obtain their phosphorus because they consume dead plants and dead snails and dead frogs. And so decomposers, like mushrooms, obtain phosphorus by feeding on the dead. And then decomposers kind of complete our cycle because they release phosphorus in their waste. And so once phosphorus is back into the soil, plants can take it in through their roots again.
And so when, before we wrap up the phosphorus cycle, I want to mention the human contribution. Humans, we're using fertilizers which contain phosphorus. We're adding fertilizers because that helps our crops grow better. Here's a picture of a farmer pulling a tractor spraying fertilizers onto his crops. It's going to help the crops grow better. So the problem is that when, when phosphorus fertilizers are used, for instance, in this animation, we're going to show, often the phosphorus will be added to the crops or to plants or even to a garden at home. And then the phosphorus simply runs off with rain. Here's a picture of some water running off of a farm and just taking away the phosphorus fertilizers that were added to help the crop. And so here's a little animation of a farmer spraying their crops with a bunch of phosphorus because again, it's one of the ingredients of fertilizers. And so now that phosphorus has been added to the crops, the problem is now that phosphorus has been added to the crops, next time it rains, the rainwater will simply carry the phosphorus downhill and eventually accumulates in this little pond that you see in my animation. Well, this often leads to an explosion of algae. This causes what are called algal blooms. Remember, phosphorus is a fertilizer, it helps plants and plant-like organisms grow. And so the algae responds to the extra amounts of phosphorus by growing. Causes what I called algal blooms. Here's a picture from overhead of an algal bloom. You can see the green layer of algae in this little watery environment here. And again, another picture, you can see how green the water looks.
So why is this bad? Well, this leads to a problem called eutrophication. And this actually causes a dead zone. So this water, which is now full of algae, ironically, life begins to suffocate. You would think, why is it suffocating? Aren't the algae photosynthetic and putting oxygen into the water? Well, that's true at first, but over time, this causes a growth of bacteria. And over time, when the bacteria die and decay, that decaying process removes a lot of the oxygen from the water. So organisms like fish literally suffocate and die. It causes a dead zone. That's the process called eutrophication. So sadly, again, because of human contributions, the phosphorus cycle is out of balance. And we hope that we can be responsible with how we use fertilizers. And so perhaps look for natural fertilizers instead of store-bought fertilizers. And, you know, you could also support organic farming and farmers' markets because these are foods that are typically grown without fertilizers and also pesticides.
Moving on to the next cycle. So the final cycle I want to mention is called the nitrogen cycle. Well, you know, there's a problem when it comes to our ability to use nitrogen. Most of the nitrogen that's in the atmosphere, by the way, 78% of our atmosphere is nitrogen gas. The problem is it's not usable. And here's a reason why: the molecule N2, the nitrogen that's in the atmosphere, it's held together by a very stable triple bond. And because it's held together by a very stable triple bond, our cells really aren't able to convert it and break it down. So there's a problem. We have to get nitrogen, but the nitrogen in the air is not usable. So we'll go over where the nitrogen then comes from. Well, why do we need nitrogen in the first place? Well, we mentioned DNA earlier in some of the other cycles, but nitrogen is one of the building blocks of DNA. We look at this picture of a nucleotide that we saw earlier. And again, DNA is made up of four nitrogen bases: A, T, C, and G. Adenine, thymine, cytosine, and guanine. They all have nitrogen in them. So the fact that DNA is made from nitrogen, it's a pretty good reason why we need it.
Well, let's go ahead and get into the cycle. So when we get into the nitrogen cycle, let's look at area one of this diagram. Well, there's nitrogen N2 in the air, but it's not available to most life on Earth. But there are some bacteria that can use it. So there are soil bacteria that will use the N2, the nitrogen in the air, and through a process called nitrogen fixation, they will convert the N2 into NH4, which is called ammonium. This process where they convert N2 into ammonium is called nitrogen fixation. Then when we move on into area two of the diagram, in area two of the diagram, there's another type of soil bacteria. They're going to use the ammonium. They're going to take in the ammonium and through a process called nitrification, they're going to convert the ammonium into NO3, which is a molecule called nitrates. So there's two very important bacteria processes that go on in the early stages of the nitrogen cycle.
Well, now let's look at area three. There's another group of bacteria there in area three. There's a group of bacteria that do a process called denitrification. Watch the animation. They'll take the NO3, they'll take the nitrates, and through the process called denitrification, they denitrify the NO3. Denitrify means take away the nitrogen. So they get rid of the nitrogen, but they keep the oxygen for their cellular needs. So when you look at the first few stages, we already have a cycle, and that's just involving in the soil bacteria. Now, what makes this process tricky, of course, is remembering the difference between nitrogen fixation, nitrification, and denitrification. But they're each soil bacteria processes, they just do a little different conversion.
So now let's look at area four of the diagram. In area four, we now have nitrogen going to the producers. NO3 are the nitrates. Plants can absorb nitrates through their roots. And once it's in the roots of plants, it simply moves up the food chain. In area five, we have a little rodent that is feeding on the plant. Nitrogen from the plant is going into the rodent. Nitrogen simply moves up the food chain. Maybe a snake eats the rodent, maybe a hawk eats the snake. Nitrogen goes up the food chain. And then we come to area six of the diagram, represented by our decomposers. Decomposers obtain nitrogen. You can see in the animation, there's nitrogen going from the rodent, nitrogen going from the plants, and they're going into the into the decomposers because decomposers feed on dead rodents and dead plants and dead everything. But every organism creates waste, and decomposers are no different. Decomposers, watch this. Decomposers in their waste will release ammonium back into the soil through a process called ammonification. And once ammonium, NH4, is back into the soil, follow the diagram. The bacteria in area two can use the NH4, ammonium, and convert it into nitrates. So again, what's hard about the nitrogen cycle are all the different processes. So just do some review.
And I'm around if you have any questions. Uh, I wanted quickly mention the role that lightning plays in the nitrogen cycle. Energy from lightning is going to break apart the N2 and break apart the O2. So watching my animation, here's some N2 and some oxygen that's in the atmosphere. And when it, uh, when lightning strikes, energy will break apart those N2s and those O2s into single Ns and single Os, single nitrogens and single oxygens. When that happens, a molecule called nitrogen oxide will form. And so nitrogen oxide, you can see has just formed. NO2 is nitrogen oxide. It's just formed. And nitrogen oxides are going to react with rain water because, you know, with lightning, usually comes rain. And so when it rains, those nitrogen oxides are going to react with rain water to form NO3, nitrates. And the nitrates simply fall down to, in the rain, to the ground. And once the nitrates are in the soil, they can be absorbed through the roots of plants, like we saw a few moments ago. So I just wanted to quickly mention the role that lightning plays in the nitrogen cycle.
So there you go. There's five biogeochemical cycles. You know, if you think I went a little quick in either the water cycle, the carbon cycle, the nitrogen cycle, or the phosphorus cycle, I have a specific video for each of those four. You may want to try watching those because I do go a little slower and take my time a little more in those specific videos. So if you're in my class, pause the video, perhaps try to answer these questions on a separate sheet of paper. I'd be happy to check your answers either before school or after school. Good luck.