The Nitrogen Cycle

Master the Nitrogen Cycle! 8th-grade biology worksheet covers fixation, nitrification, ammonification, and denitrification.

The Nitrogen Cycle Why is nitrogen important? Which processes allow nitrogen to cycle through the atmosphere? What organisms are crucial to the proper cycling of nitrogen? After watching the video, complete the summary below by typing in the missing words into the paragraph. The word choices are below the paragraph. You may also use this image as another resource to complete the paragraph below. Nitrogen is everywhere! In fact, N2 gas makes up about 78% of Earth's atmosphere, we often think of as "air". But having nitrogen around and being able to make use of it are two different things. Your body, and the bodies of other plants and animals, have no good way to convert N2 gas from the atmosphere into a usable form. Still, DNA and proteins in your body contain quite a bit of nitrogen. Where does that nitrogen come from? In the natural world, it comes from bacteria (AKA: prokaryotes)!Bacteria (AKA: Prokaryotes) play a key role in the nitrogen cycle.Nitrogen enters the living world by way of water or soil bacteria, which convert (change) atmospheric nitrogen—N2 gas—into biologically usable forms in a process called nitrogen fixation. Some species of nitrogen-fixing bacteria are free, living in soil or water, while others live inside of legume plants. Some examples of legume plants include various types of peas, beans, nuts, lentils, etc.Nitrogen-fixing bacteria convert (change) atmospheric nitrogen gas into ammonia—NH3—which can be taken up by plants and used to make organic molecules, such as proteins and DNA. This is called assimilation. Once the plants have the nitrogen, animals get the nitrogen by consuming (eating) the plants. Animals use some of the nitrogen to make their own proteins and DNA, and some nitrogen is broken down and excreted as waste, such as the urea found in urine.When living organisms die, the nitrogen in their bodies doesn't remain forever in their bodies. Instead, it's converted (changed) from organic nitrogen (such as proteins and DNA) back into N2 gas by bacteria. This process often involves several steps in terrestrial (land) ecosystems. Nitrogenous compounds from dead organisms or fecal and urine wastes are converted into ammonia—NH4—by decomposers such as bacteria and fungus. This process is called ammonification. Then, the ammonia is converted into nitrites (NO2) and nitrates (NO3) by the nitrifying bacteria (prokaryotes). This process is called nitrification. In the end, the nitrates (NO3) are made into N2 gas by denitrifying prokaryotes (bacteria) by the process called Denitrification. The Nitrogen Cycle Complete the image by labeling the following processes:Denitrification Nitrogen Fixation NitrificationAssimilation Ammonification Denitrification Assimilation Nitrogen Fixation Nitrification Ammonification