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 The Carbon Cycle and The 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.

---

by Mary LeFever

Mary LeFever is a resource specialist for the Middle School Portal, and a doctoral candidate in science education at Ohio State University. She has taught middle school and high school science and is an adjunct instructor of biology and natural sciences at Columbus State Community College. Please email any comments to msp@msteacher.org.

---

 Back to top

Copyright July 2007 — The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0424671. 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.

This work is licensed under a Creative Commons License.