MiddleSchoolPortal/What Goes Around Comes Around: Nitrogen Cycle

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What Goes Around Comes Around:The Nitrogen Cycle - Introduction

This is the third publication in our series called What Goes Around Comes Around. The first publication covers the topic of the carbon cycle and the second, water cycle.

Do your students know each breath we take is pretty much a waste? Are they aware that 79 percent of the air we breathe is useless to us? That's because 79 percent of the atmosphere is inert N2.We breathe it in, then right back out—unchanged.

The gas we do need, oxygen, makes up only 20 percent of the atmosphere. Commonly, our students equate the atmosphere, or air, with oxygen, unaware that atmospheric nitrogen is as essential to living things as carbon and water. This publication will provide you with resources designed to help students gain knowledge regarding nitrogen, how it cycles, and its biological importance.



As with the water and carbon cycles, the nitrogen cycle does not fit neatly into a single discipline such as physical science. Although nitrogen is an element with chemical and physical properties, it also is a necessary component of proteins produced by living things. As mentioned earlier, nitrogen is the major component of the atmosphere, an earth science concept. A study of the nitrogen cycle thus touches on the physical, life, and earth science content standards of the National Science Education Standards, providing an opportunity for interdisciplinary study.

Compared to the water and carbon cycles, the nitrogen cycle is more abstract. Where water and carbon are potentially tangible and familiar, nitrogen is not. Students will require thorough scaffolding and frequent encouragement in order to construct a concept of nitrogen and its role in living systems. If students have good grasps of the water and carbon cycles, they should more easily conceptualize the nitrogen cycle by using the same successful learning strategies they used with those less abstract cycles. (See What Goes Around Comes Around: Carbon Cycle and What Goes Around Comes Around: Water Cycle in this series, What Goes Around Comes Around.)

We suggest an integrated approach to teaching the nitrogen cycle. By this we mean breaking down the artificial categorization of the nitrogen cycle as strictly an earth or life science concept. Deliberately emphasizing the ways the nitrogen cycle involves concepts of life, earth, and physical science assists students in transferring science content knowledge from one context to another. True learning, some education experts assert, is the ability to transfer and apply content knowledge from one context to another.

Students will need some background knowledge in order to assimilate nitrogen cycle knowledge. They need some familiarity with bacteria, specifically that they are microscopic, single-celled organisms that take in nutrients, perform chemical changes to the nutrients, grow and reproduce, and get rid of waste like all other living things. The exceptional aspect of these bacteria, however, is that they do not necessarily take in oxygen and give off carbon dioxide as is usually understood to happen in nonphotosynthetic living cells. Be prepared to help students substitute the intake and output nutrients of these bacteria for the usual oxygen and carbon dioxide.

Students also need an understanding of symbiosis, since many of these bacteria live symbiotically, especially within the roots of leguminous plants. Students should understand the difference between element and compound. You may wish to avoid representation of the important nitrogen compounds using formulas if you feel this would only confuse students. Finally, prior mastery of the carbon and water cycles will position students well for learning about the nitrogen cycle.

This publication provides a variety of resources: some assist you in your content knowledge, some are actual lessons or activities, some are good graphic representations of both concepts and organisms of the nitrogen cycle, and some provide real data from current issues for you and your students to analyze and interpret. We hope you find this breadth of resources helpful in teaching students about the importance of the nitrogen cycle to life on this planet.

The first resource helps you see one of several contexts for the nitrogen cycle: the flow of matter in ecosystems. The NSDL Strand Map Service provides maps that illustrate connections between concepts and across grade levels. An image of the middle grades (6-8) only part of the Flow of Matter in Ecosystems map appears below. Clicking on a concept within the maps will show NSDL resources relevant to the concept, as well as information about related AAAS Project 2061 Benchmarks and National Science Education Standards. Move the pink box in the lower right hand corner of the page to see the grades 6-8 learning goals. Other teaching contexts for the nitrogen cycle include common themes such as Systems, Constancy and Models, Diversity of Life and Atoms and Molecules.

Flow of Matter in Ecosystems

View individual map Printable view of map

Background Information for Teachers

This section provides resources to enhance your content knowledge of each of the processes and compounds involved in the nitrogen cycle. The first resources are quick reminders of the structure of DNA and proteins—the essential macromolecules of living things which require nitrogen and a big reason we are interested in familiarizing students with the nitrogen cycle. A second reason for learning about the nitrogen cycle is related to nitrogen-containing pollutants and the role of human activity in the nitrogen cycle, for which we also provide resources in this section.

Nucleic Acids: DNA and RNA This lesson is an introduction to the structure and function of DNA, including the process of DNA replication.

The Biotechnology Project: Chapter 2: Protein Structure This chapter provides a brief background into the structure of proteins and how this structure can determine the function and activity of proteins. It is not intended to substitute for the more detailed information provided in a biochemistry or cell biology course.

The Nitrogen Cycle: Of Microbes and Men This module provides an overview of the nitrogen cycle and the chemical changes that govern the cycle.

Teaching Issues and Experiments in Ecology: Human Alteration of the Global Nitrogen Cycle In this unit, aimed at undergraduates, students explore large-scale anthropogenic changes to the nitrogen cycle by examining studies that document anthropogenic inputs of nitrogen globally, nitrogen saturation of temperate forests, the export of nitrogen from rivers to the ocean, and the ecology of Pfiesteria in the Chesapeake Bay. Click on the "Figure Set" tab to find four questions for inquiry and reference articles for each question.

Unit 9 Soil Organisms and Nitrogen Cycle: Chapter 2 Nitrogen Cycle This chapter is about the important role soil bacteria play in providing nitrogen for plant growth via the nitrogen cycle. The cycle moves atmospheric nitrogen into organic N, converts it into ammonia N and next into nitrate N, and finally back to atmospheric N. Color line drawings and photographs of plants and bacteria enhance the text. You may wish to use some of the images and text to provide students with textual material.

The Important Nutrient Nitrogen If you want greater detail than is provided in the resource above, read this seven-page learning module aimed at undergraduates who are not science majors. It describes the nitrogen cycle and illustrates the details with line drawings, giving you background information and positioning you to make good decisions regarding which content you wish for your students to learn and how. (This is a page from the Global Change Instruction Program.)

Lessons and Activities

In this section, a deductive approach is used to introduce students to the nitrogen cycle. Some resources featuring soil bacteria are followed by discussions of nitrogen compounds and then the element N itself. In this way, we move from the concrete and familiar to the more abstract, less familiar aspects of the nitrogen cycle.

BIOL/CSES 4684 Pseudomonas:Nitrosomonas Soil Microbiology Phase contrast and scanning electron images of the bacteria are provided. Descriptions of the organism's characteristics, taxonomy, and ecology are provided. Additional references and related links are included.

National Teacher Enhancement Network: An Investigation into Effects of Rhizobium Soil Bacteria on Nitrogen Availability This experiment will make use of a soil bacterium of the genus Rhizobium and a host legume to demonstrate the effects that soil microbes can have on soil fertility and nutrient availability. According to the learner outcomes, students should be able to: collect, record and interpret their data; identify the control and the variables in the experiment; describe the growth of plants with and without nitrogen-fixing bacteria; and name the bacterium responsible for making nitrogen available to the plant.

The Nitrogen Cycle The nitrogen cycle is not restricted to terrestrial ecosystems. Though this is a commercial site, the article is a comprehensible discussion of the nitrogen cycle in the context of aquatic environments, emphasizing the importance of enhancing conditions to promote nitrogen-fixing bacteria growth. Students may be able to pair up and conduct a self-guided reading and thinking activity with this article, before or after completing the experiment described in the resource Lesson 1: Nitrogen Cycling above.

The Facts about Ammonia At first glance this fact sheet from the New York State Department of Health may seem outside the context of your discussion of the nitrogen cycle. However, students are often curious about the nitrogen-containing compounds that appear in representations of the nitrogen cycle. Use of this resource allows for connections from familiar household ammonia to ammonia’s role in the nitrogen cycle. The fact sheet is intended to provide general awareness and education on a specific chemical agent.

Nitrate and Nitrite A two-page article from Argonne National Laboratory can address student curiosity regarding nitrate and nitrite, significant compounds in the nitrogen cycle. It focuses less on chemistry and more on these compounds’ environmental significance and is appropriate to middle school students. It may serve as an introduction to discussion of the relationship between humans and the nitrogen cycle. Included in the article are nitrates and nitrates uses, sources, effects on human health, and where to find additional information.

Human Activity, the Nitrogen Cycle and Global Issues

As with the carbon and water cycles, human activity can tip the balance in these natural cycles. Some examples are: manipulation of crops to enhance nitrogen content of soils; excess fertilizer runoff, which enhances stream and river algal and plant growth; and by-products of technology that produce nitrogen compounds which become pollutants in high concentrations. You may have your students investigate these real-world phenomena, apply their knowledge of not only the nitrogen cycle but the water and carbon cycles as well, and thereby, demonstrate knowledge of the complexity of the problems by explaining the causes, effects and possible solutions.

Measuring Nitrates and Their Effect on Water Quality This self-contained lesson could be done by middle school students in pairs. In this social approach to learning, students can help each other understand the content and share their interpretations and reactions. The module is from a larger series on water quality investigations. It provides background information on nitrates and how they affect water quality. It also contains a pre-test and a post-test, a laboratory investigation, and a self-study game. The purpose of the site is to help students understand and describe the sources of nitrates and the role they play in an ecosystem and the effects of excess nitrates on water quality and human health. Students will also learn how to measure, graph, and interpret the direct and indirect effects of nitrates on fish.

Science Wire from the Exploratorium and Public Radio International: Agroecology—An Alternative to Herbicides and Genetics One of the promises of genetically modified (GM) food is that it helps minimize the need for pesticides and fertilizers, and may help reduce the threat to future food supplies. But opponents of GM food say that solution poses more problems than it solves. In the third installment of a series on GM food, a science reporter visited a farm where agroecology is being tested.

1900 Air Pollution Gases trapped in ice cores show the dramatic impact that human activities have had on the planet since the Industrial Revolution. This graph, from the web site accompanying the Frontline/NOVA special "What's Up with the Weather?," reveals how atmospheric carbon dioxide, methane, and nitrous oxides from coal- and oil-burning power plants, cars, and other fossil-fuel-burning sources have climbed along with the world population, with as yet unknown effects on the climate system.

SMARTR: Virtual Learning Experiences for Students

Visit our student site SMARTR to find related science-focused virtual learning experiences for your students! The SMARTR learning experiences were designed both for and by middle school aged students. Students from around the country participated in every stage of SMARTR’s development and each of the learning experiences includes multimedia content including videos, simulations, games and virtual activities.


The FunWorks Visit the FunWorks STEM career website to learn more about a variety of science-related careers (click on the Science link at the bottom of the home page).

National Science Education Standards

A study of the nitrogen cycle touches on the physical, life, and earth science content standards of the National Science Education Standards.

Science as Inquiry: Content Standard A

As a result of activities in grades 5-8, all students should develop:

Abilities necessary to do scientific inquiry

  • Identify questions that can be answered through scientific investigations.
  • Design and conduct a scientific investigation.
  • Use appropriate tools and techniques to gather, analyze and interpret data.
  • Develop descriptions, explanations, predictions, and models using evidence.
  • Think critically and logically to make the relationships between evidence and explanations.

Understandings about scientific inquiry

  • Different kinds of questions suggest different kinds of scientific investigations. Some investigations involve observing and describing objects, organisms, or events; some involve collecting specimens; some involve experiments; some involve seeking more information; some involve discovery of new objects and phenomena; and some involve making models.

Physical Science: Content Standard B

As a result of their activities in grades 5-8, all students should develop an understanding of:

Properties and changes of properties in matter

  • Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances often are placed in categories or groups if they react in similar ways; metals is an example of such a group.
  • Chemical elements do not break down during normal laboratory reactions involving such treatments as heating, exposure to electric current, or reaction with acids. There are more than 100 known elements that combine in a multitude of ways to produce compounds, which account for the living and nonliving substances that we encounter.

Life Science: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of:

Structure and function of living things

  • Cells carry on the many functions needed to sustain life. They grow and divide, thereby producing more cells. This requires that they take in nutrients, which they use to provide energy for the work that cells do and to make the materials that a cell or an organism needs.

Regulation and behavior

  • All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.
  • Regulation of an organism's internal environment involves sensing the internal environment and changing physiological activities to keep conditions within the range required to survive.

Populations and ecosystems

  • A population consists of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.
  • Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some micro-organisms are producers—they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.
  • The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem.

Earth and Space Science: Content Standard D

As a result of their activities in grades 5-8, all students should develop an understanding of:

Structure of the earth system

  • Soil consists of weathered rocks and decomposed organic material from dead plants, animals, and bacteria. Soils are often found in layers, with each having a different chemical composition and texture.
  • The atmosphere is a mixture of nitrogen, oxygen, and trace gases that include water vapor. The atmosphere has different properties at different elevations.
  • Living organisms have played many roles in the earth system, including affecting the composition of the atmosphere, producing some types of rocks, and contributing to the weathering of rocks.

Science in Personal and Social Perspectives Content Standard F

As a result of their activities in grades 5-8, all students should develop an understanding of:

Personal health

  • Natural environments may contain substances (for example, radon and lead) that are harmful to human beings. Maintaining environmental health involves establishing or monitoring quality standards related to use of soil, water, and air.

Natural hazards

  • Human activities also can induce hazards through resource acquisition, urban growth, land-use decisions, and waste disposal. Such activities can accelerate many natural changes.

Risks and benefits

  • Students should understand the risks associated with natural hazards (fires, floods, tornadoes, hurricanes, earthquakes, and volcanic eruptions), with chemical hazards (pollutants in air, water, soil, and food), with biological hazards (pollen, viruses, bacterial, and parasites), social hazards (occupational safety and transportation), and with personal hazards (smoking, dieting, and drinking).

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Author and Copyright

Mary LeFever is a resource specialist for the Middle School Portal 2: Math & Science Pathways project, a doctoral candidate in science education at Ohio State University, and presently teaches high school biology. She has taught middle school science and biology and natural sciences at Columbus State Community College.

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Copyright July 2007 - The Ohio State University. Last updated September 19, 2010. This material is based upon work supported by the National Science Foundation under Grant No. 0424671 and since September 1, 2009 Grant No. 0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.