Transcript:
Because the earth is finite, matter has to be reused and recycled over and over again. So, the atoms that are in you, were once in the air, in soil, in water, and in rocks. These atoms have also been used by countless other living things, from dinosaurs, to broccoli plants, to Abraham Lincoln. And after they leave you, they will become part of other living things or of the environment. This recycling of matter is known as a nutrient cycle and there are several different nutrient cycles for different elements. Today, we will focus on the nitrogen cycle, the process by which the element nitrogen moves around in ecosystems.
The nitrogen cycle is crucial for all life on earth because nitrogen is needed to make some of the most important molecules for life, including DNA, RNA, and proteins that are needed by ALL living things. Without nitrogen, there would be, literally, no life as we know it. So, it’s important to understand at least a little bit about how the nitrogen cycle works, right? Let’s get into it!
Nitrogen Gas (N2) makes up about 78% of our atmosphere. You breathe it in and out all the time. In fact, you’re doing it right now! The problem with N2 is that you can’t use it to make any of the cool molecules we just discussed. The 3 bonds between the nitrogen atoms in N2 make it very hard to break apart so you can’t do any reactions to make DNA, or RNA, or proteins, or anything else. The nitrogen atoms are essentially superglued together.
Luckily, there are certain bacteria that can break the triple bond of nitrogen gas to make something that organisms can use. These bacteria are called nitrogen-fixing bacteria and they are found in the soil and in root nodules of certain plants known as legumes, as well as a few other places. These nitrogen-fixing bacteria break nitrogen gas apart and add hydrogen atoms to it to form ammonia (NH3), or ammonium (NH4+).
This process moves nitrogen from the air to the soil and is called nitrogen fixation because the nitrogen in the air is getting “fixed” so that other living things can use it!
Ammonia can be taken up by plants and used to make important biological molecules like DNA and proteins etc. This process of uptake and production of biological molecules is called assimilation.
But not all of the ammonia produced by nitrogen fixation gets assimilated into plants. Too much ammonia can be toxic, and sometimes plants prefer to assimilate other nitrogen compounds called nitrates. Our next step is the conversion of ammonia into nitrates, a process called nitrification.
Nitrification is done by nitrifying bacteria. These bacteria oxidize or add oxygen to ammonia in chemical reactions that first convert the ammonia to nitrite (NO2-) and then to nitrate (NO3-). Because oxygen is needed for these reactions, nitrification happens best in soils that are well-aerated.
Like ammonia, nitrate is a plant fertilizer because it can be assimilated and used to make key biomolecules (DNA, RNA, Proteins etc.).
Once nitrogen is inside of plants and used to build our sweet biomolecules, it can pass to other living things through food webs. When an animal eats the plant, the nitrogen-containing compounds in the plant move to the animal. When that animal gets eaten, nitrogen moves to its predator, and so on.
Eventually, all living things die and decompose. This returns the nitrogen back to the soil as ammonia in a process called ammonification. This ammonia can now be used again by plants or converted to nitrates by nitrification. And so, nitrogen gets cycled around and around, over and over again.
But we are still missing one key part of our cycle. In order to have a complete cycle, nitrogen gas needs to get back into the air. This is done by denitrifying bacteria and is called denitrification. During denitrification, bacteria convert nitrates (NO3-) into nitrogen gas (N2). Denitrification happens best in low oxygen environments, like waterlogged soils, and it reduces the fertility of the soil. This is one reason why it is harmful to overwater plants...
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00:00 Intro to Cycles
00:31 The Nitrogen Cycle
01:05 Nitrogen Fixation
02:29 Assimilation of Ammonia
02:42 Nitrification
03:33 Assimilation of Nitrates
03:45 Food Chain Movement of Nitrogen and Ammonification
4:20 Denitrification
05:00 Quick Review
Credits:
Soil background image: Image by brgfx on Freepik
Legume root nodule image: Frank Vincentz, CC BY-SA 3.0 via Wikimedia Commons
Earth Rotating Clip: Video by freepik
Brocolli pic:Image by Racool_studioon Freepik
Dinosaur: Image by wirestock on Freepik
Cat animation: by Freepik
BIRD ANIMATION: Image by Freepik
Sound Effect from Pixabay
Violin Music by FreqMan (sampled and shortened to fit relevant part of video) : freesound.org/people/FreqMan/...