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ZingPath: Cycling of Matter

Nitrogen Cycle

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Lesson Focus

Nitrogen Cycle

Life Science

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You will get to learn about natural resources by focusing on renewable and nonrenewable sources of energy. To test your understanding, you will then be responsible for meetingthe energy needs of a small island.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Describe the flow of matter through the nitrogen cycle,
  • Summarize the role of microorganisms in the nitrogen cycle,
  • Summarize the role of producers and consumers in the nitrogen cycle.

Everything You'll Have Covered

Because most organisms cannot absorb nitrogen gas from the air, bacteria help convert nitrogen gas into a nitrogen compoundscompound in the soil. Describe how nitrogen-fixing and nitrifying bacteria help do this.

~ First, nitrogen enters the soil from lightning bolts and rainfall. Nitrogen-fixing bacteria such as the swellings on roots of leguminous plants like peas and beans, contain enzymes that convert nitrogen gas into ammonia. Nitrifying bacteria areis another type of bacteria that live in the soil. Nitrifying bacteria oxidize ammonia and convert it first into nitrites (NO?-)?-), and then into nitrates (NO3-). The nitrates are then absorbed, or "assimilated," by plants. This process is called assimilation. Animals consume the plants, and, in turn, consume the nitrogen compounds in the plants.

Describe the process of ammonification.

~ Waste, such as animal urine and dead plants and animals, is converted into nitrogen compounds by decomposers. Decomposers convert waste and dead plants and animals into organic and inorganic molecules. One of the inorganic molecules they produce is ammonia.

What makes the process of denitrification different from ammonification, nitrogen fixation, and nitrification?

~ Denitrification is the process of converting nitrates, which are produced by nitrifying bacteria, into nitrogen. Denitrification does not require oxygen. Ammonification, nitrogen fixation, and nitrification all rely on oxygen for the process to be completed.

Describe the nitrogen cycle.

~ Nitrogen gas from the atmosphere enters the soil through lightning bolts and rainfall. Nitrogen-fixing bacteria convert the nitrogen in the soil into ammonia through a process called nitrogen fixation. Decomposers also produce ammonia by converting animal waste and dead plants and animals into organic and inorganic materials, including ammonia. Nitrifying bacteria then oxidize the ammonia and first convert it into nitrites and then nitrates. The nitrates can beare then absorbed by plants which, in turn, are eaten by animals. When no oxygen is present, other types of bacteria convert nitrates into nitrogen gas in a process called denitrification. The nitrogen gas then returns to the atmosphere.

Nitrogen is a key compound for living things, and disruption of the nitrogen cycle can lead to serious problems. Give one example of a human activity that can disrupt the nitrogen cycle and the consequences of this.

~ Combustion such as burning fossil fuels can disrupt the nitrogen cycle. Burning fossil fuels increases concentrations of nitrogen in the atmosphere, which can turn into smog and acid rain when it reacts with the air. The overuse of nitrogen-containing fertilizers in agriculture disrupts the cycle by adding more nutrients to the environment than are naturally present. Agricultural runoff disrupts aquatic ecosystems. 

Tutorial Details

Approximate Time 2 Minutes
Pre-requisite Concepts Students should have an intellectual grasp on the following terms: ammonification, assimilation, and consumer.
Course Life Science
Type of Tutorial Animation
Key Vocabulary ammonification, assimilation, consumer