The Nitrogen Cycle | Environmental Chemistry | Chemistry | FuseSchool NARRATOR: Nitrogen is essential to life. Plants and animals need nitrogen to make proteins. And proteins are building blocks of cells and, therefore life. Nitrogen makes up 78% of the air, however, neither plants nor animals can take nitrogen directly from the air, because nitrogen is so unreactive. However, plants are able to take nitrogen compounds such as nitrates in the soil. And then animals eat these plants, therefore providing animals with a source of nitrogen. In this video, we're going to look at the nitrogen cycle. This is the movement of nitrogen for the environment. Nitrogen is continually cycled through the air, soil, and living things. The process of nitrogen in the atmosphere being turned into nitrogen in the soils is called fixing. Here are four different ways in which nitrogen fixing occurs naturally. Firstly, nitrogen-fixing bacteria in the soil turns nitrogen from the air into nitrates. Which to plants, then absorb. Some plants, such as the legume family-- which includes peas, beans, and clover-- have these nitrogen-fixing bacteria their root nodules. Secondly, decomposers in the soils break down animal excretion and dead organisms, returning nitrogen back to the soil as ammonia. The ammonia turns first into nitrite, and then nitrifying bacteria in the soils turns the nitrite into nitrate. Thirdly, lightning can cause chemical reactions in the atmosphere. There's also nitrogen reacting with oxygen to produce nitrous oxide. The nitrous oxide then reacts with more oxygen, and dissolves in rainwater to make nitrous acid. This rainwater, containing nitrous acid, increases the amount of nitrate in the soil. Burning fossil fuels also adds nitrous oxide to the atmosphere, resulting in nitric acid. This is of course, not a natural way of nitrogen fixing. And finally, in the oceans, many species of blue green algae, also called cyanobacteria, can fix nitrogen. They then provides source of nitrogen to aquatic animals. And the nitrogen goes around a similar cycle to what happens on land. These are the natural ways in which nitrogen fixing occurs. The Haber process, which is how fertilizers are made, makes up approximately 30% of the nitrogen fixing. Because nitrogen is essential for making proteins, proteins are essential for cell production, cell production is how growth occurs. Fertilizers are therefore used to increase the nitrates in the soil to maximize plant growth. Watch our videos on the Haber process to learn more about this. And as I mentioned earlier, burning fossil fuels also adds nitrous oxide to the atmosphere. Which dissolves rainwater to make nitric acid, which then adds nitrates to soils. This isn't as good as it sounds. It upsets the balance of the natural nitrogen cycle. Pollutant ecosystems are alternating the ecology of entire regions. Too much nitrogen in the soil makes it more acidic. The nitrogen also passes into rivers and lakes, where it's considered a pollutant. In some conditions, such as waterlogged soils, denitrifying bacteria in the soil break down nitrates and return nitrogen back to the air. This reduces the fertility of the soil. So from this video, you should now understand how the nitrogen cycle works. Nitrogen is essential to life, and some needs to be fixed in nitrates for plants, and therefore animals to access it. Nitrogen is continually cycled through the air, soil, living things, and water systems.