hey everybody it's mr smeeds and today we'll be covering topic 1.5 which is the nitrogen cycle so just like our coverage of the carbon cycle yesterday we'll be focused on the sink sources and reservoirs of the nitrogen cycle but throughout the video we'll point out how the nitrogen cycle differs from the carbon cycle in some really important ways our objective today is to be able to explain the steps and reservoir interactions in the nitrogen cycle and the skill that we'll be practicing with the frq at the end of the video is going to involve explaining relationships between different characteristics of environmental concepts that are represented visually so we'll continue that focus on visual models like we did with the carbon cycle yesterday so just like with the carbon cycle the nitrogen cycle is the movement of nitrogen molecules between sources sinks and reservoirs as a reminder the sources are things or processes that release nitrogen into the atmosphere and sinks take in increasing amounts of nitrogen now a big key difference between the nitrogen and the carbon cycle is that nitrogen reservoirs generally hold nitrogen for a relatively short period of time when compared with the carbon cycle so think about the fossil fuels and sedimentary rocks like limestone or sandstone in the carbon cycle that could hold carbon for millions of years in the nitrogen cycle most of the reservoirs are going to hold nitrogen for a relatively short period of time so we can look at some examples such as plants or soil or the atmosphere so plants are only going to hold nitrogen as long as they're alive then when they die the nitrogen is returned to the soil and that nitrogen does not stay in the soil for very long because it's taken right back up by plants for growth nitrogen also exists in the atmosphere in fact that's the biggest reservoir of nitrogen about 78 of the atmosphere is made up of nitrogen and a really important key detail to know about this nitrogen in the atmosphere is that most of it exists in the form of n2 gas now this is not a form that's usable by plants or animals our final key detail here to know about the nitrogen cycle is that nitrogen is a key limiting nutrient for plants and animals so all living things need nitrogen in order to make the dna that goes in every one of their cells and to make the amino acids that build the proteins that their bodies are made out of and so we have kind of a problem here and that's that all living things need nitrogen and the atmosphere is the biggest reservoir of nitrogen but almost all of that nitrogen in the atmosphere exists in n2 gas which is not usable by plants or animals so the answer to this question is nitrogen fixation it's the first step in the nitrogen cycle and it is the most critical for life on earth so it's the process of this nitrogen gas from the atmosphere being converted into biologically usable nitrogen which is a form that can be taken in by plants and that's nh3 ammonia or no3 which is nitrate so this can happen in a few different ways it can happen both naturally and synthetically naturally it can either be done by nitrogen fixing bacteria or by lightning storms which can actually cause some of that nitrogen in the atmosphere to be converted to ammonia but it's primarily done by bacteria in the natural sense so we'll talk about two different types of bacteria that can do that now first is bacteria that live freely in the soil and so we can see that in the diagram if we look here there are nitrogen fixing bacteria that live in the soil they can convert nitrogen in the atmosphere into ammonium but there are also bacteria that live in symbiotic relationships with certain plants now those are going to be plants that are known as legumes so those are species like peas and beans they actually have little nodules in their roots that the bacteria live in and the bacteria fix nitrogen for these plants in exchange for amino acids that they use to build the proteins they need so remember symbiosis is a relationship where organisms are living closely with one another and in this case it's mutualistic because it benefits both species so that's a very important form of natural nitrogen fixation so if we look at the diagram we'll notice this blue arrow around atmospheric nitrogen again it can be done by lightning but it's primarily done by bacteria whether that's bacteria that live freely in the soil or bacteria that live in the root nodules of certain plants then we also have synthetic nitrogen fixation and this is where humans combust fossil fuels in order to fix nitrogen gas from the atmosphere into nitrate so this is no3 this is very energy intensive but it allows humans to produce synthetic fertilizers which contain nitrates and then we can spread over our crops to increase our agricultural yields or the amount of food that we produce so if we look at the diagram here we'll see in red we have this factory to symbolize that this is an industrial process remember it requires a lot of energy input and then it's going to produce nitrates which we'll use as fertilizers in agriculture so while nitrogen fixation is a critical step to understand and we spent a lot of time focusing on it there are other steps in the nitrogen cycle that we'll talk about now so the first one is assimilation assimilation is the process of plants and animals taking nitrogen in and incorporating it into their bodies so remember that they need nitrogen in the dna in their cells they also need it to build the proteins that make up their bodies so plants are able to access nitrogen directly by having their roots either take in nitrates or ammonia from the soil animals though have to eat plants in order to get their nitrogen or if they're a carnivorous animal they need to eat animals that have eaten other plants so it all starts with plants they are the key assimilators of nitrogen so if we take a look at the diagram we'll see in the blue circles here nitrogen is going to move from the soil into plants roots and into the plant's body and then animals will eat the plant and that's how they assimilate nitrogen then we have a monofication a monofication is kind of the opposite in that it is soil bacteria microbes and decomposers converting waste and dead biomass so dead organisms back into ammonia that returns to the soil so just like in the carbon cycle we had the cycling of carbon between photosynthesis and respiration we have something similar in the nitrogen cycle where organisms assimilate or take in nitrogen but when they die or produce waste then the bacteria in the soil and the decomposers break that waste down and they return the nitrogen that was in the biological matter back to the soil through a monofication so if we look at the circle in green here we can see again these dead animals dead plants or their waste just gets returned to the soil to ammonia by these decomposers and other soil microbes next we'll talk about nitrification nitrification is the process where ammonium nh4 is converted into nitrite or no2 and then eventually into nitrate no3 now this is also done by soil bacteria so i hope you're sensing a trend here in the nitrogen cycle and that's that bacteria are very critical at almost every step of the process so we can see that process of nitrification outlined here in the orange circle and then finally we have denitrification denitrification is the conversion of soil nitrogen specifically nitrate back into a gas form however this is going to be the gas form nitrous oxide or n2o and so this is going to be converted again by bacteria releasing the atmosphere and eventually that nitrous oxide can break down to form nitrogen gas and we've completed the cycle now we'll wrap up by talking about some human impacts on the nitrogen cycle so humans have an impact on the climate through the nitrogen cycle by the release of nitrous oxide nitrous oxide is a greenhouse gas which means that it traps heat in earth's atmosphere and warms it up now it's produced by agricultural soils so when humans clear land and till the soil to plant their crops the bacteria in the soil are going to through denitrification turn the nitrates in the soil into nitrous oxide this is especially prevalent when the soil is waterlogged or over irrigated and so by the growing and production of human food we contribute to greenhouse gases particularly nitrous oxide then there's ammonia volatilization so this is where excess fertilizer can lead to ammonia gas actually entering the atmosphere this creates a couple issues one is acid precipitation so the ammonia can combine with water in the atmosphere fall to earth as acidic rain and that can create a lot of environmental issues and there's also a human health consequence ammonia gas in the atmosphere can combine with other pollutants and can irritate the respiratory tracts of humans and it's also just lost nitrogen from the agricultural fields themselves which results in lost profits for farmers and finally we have the issue of leaching and eutrophication so when we use synthetic fertilizers we're often over applying nitrates to the soil and we're putting more nitrates in the soil than it can hold so this leads to something called leaching which is where rainwater or irrigation water carries the nitrates right out of the soil think of it as kind of washing them or flushing them right out of the soil and that agricultural runoff can enter local bodies of water like streams or lakes and what happens is all of this excess nitrogen fuels aggressive algae growth to the point that the algae covers the surface of the water and it actually blocks the sunlight so that aquatic plants below the surface don't get the sunlight they need which can kill those plants for q 1.5 today we're going to be looking at explaining the relationships between different characteristics of an environmental concept so i want you to try to describe one chemical transformation that occurs in the natural nitrogen cycle and then explain the importance of that transformation to an ecosystem all right everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain write like a scholar