The Nitrogen Cycle

Master the Nitrogen Cycle! Explore its vital role in ecosystems and biology.

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? What happens if the cycle is disrupted? After watching the video, complete the Cloze summary below by typing in the missing words into the paragraph. Use the following word bank: ammonia, animals, DNA, decomposition, denitrifying, die, lightning, nitrifying (2), nitrogen-fixing bacteria, oceans, organisms, plants, proteins, soil. Approximately 80% of the molecules in Earth’s atmosphere are made of nitrogengas. Most of the nitrogen on Earth is in the atmosphere, however, nitrogen is stored in reservoirs such as living organisms,soils, and oceans.All plants and animals need nitrogen to make amino acids, proteinsand DNA,but the nitrogen in the atmosphere is not in a form that they can use. The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightningstrikes or fires. They can also be converted into usable nitrogen (nitrates and nitrites) by denitrifyingbacteria, nitrifyingbacteria, and nitrogen-fixing bacteria,which is associated with the root nodules of legume plants.Other plants get the nitrogen they need from the soilor water in which they live mostly. Nitrogen is required for plant growth, and therefore it is a limiting factor. Animalsget the nitrogen they need by consuming plants or other animals that contain organic molecules composed partially of nitrogen. Excess nitrogen is excreted (or eliminated) by animals into the soil. In addition, when organisms die,their bodies break down through a process called decompositionwhich returns the nitrogen to the soil on land or into the oceans. As dead plants and animals decompose, nitrogen is converted into inorganic forms like ammonia.The ammonium salts are absorbed onto clay in the soil and then chemically altered by nitrifyingbacteria. Roles of Organisms in the Nitrogen Cycle Using the image above, explain each organism's role in the nitrogen cycle, by filling in the column to the right in the chart below. Denitrifying bacteria Nitrifying bacteria Nitrogen-fixing bacteria (root nodules or soil) Decomposers (like fungi and bacteria) Plants Animals Describe two different ways in which the nitrogen cycle could be disrupted and explain the consequences of these disruptions.