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18.3: Lesson 18.2: Cycles of Matter

Difficulty Level: At Grade Created by: CK-12
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Key Concepts

  • Elemental carbon
  • Carbon cycle
  • Nitrogen cycle

Lesson Objectives

  • Explain why carbon is important to life.
  • Outline the carbon cycle.
  • Give an overview of the nitrogen cycle.

Lesson Vocabulary

  • carbon cycle: continuous cycle in which carbon moves through living and nonliving things, including the atmosphere and fossil fuels
  • dead zone: area in a body of water where nothing grows because there is too little oxygen
  • nitrogen cycle: continuous cycle in which nitrogen moves through living and nonliving things, including the atmosphere and soil

Teaching Strategies

Introducing the Lesson

Introduce the carbon and nitrogen cycles by reviewing the elements carbon and nitrogen. Share some of the information about these two elements that is provided at the URL below. Then tell students they will learn in this lesson how these two types of matter cycle through ecosystems.




Give students a detailed visual overview of the carbon cycle by showing them the animated Carbon Cycle Cartoon at this URL: http://www.neok12.com/php/watch.php?v=zX670b656f7c786e7d674f63&t=Carbon-Cycle.


The activity at the following URL uses a game to introduce students to the carbon cycle. It will help them see how carbon in the atmosphere is connected to living things. Specific activity objectives are for students to describe the carbon cycle, the journey a carbon atom might take on its way through the cycle, and how trees help to store carbon.


Differentiated Instruction

Work with students to make simplified cycle diagrams of the biotic and abiotic carbon cycles. Their diagrams can be based on the carbon cycle diagram in the FlexBook® lesson, but they should include less detail. For example, the amount of carbon stored in various reservoirs should not be included. Tell students to keep their cycle diagrams in their science notebook.


Ask a group of students to do the nitrogen cycle role-playing activity on pages 40–45 of the PDF document below. Through the role-play, the students will consider the agricultural and environmental consequences that occur when the nitrogen cycle is interrupted. After students prepare for the role-play, set aside 20 minutes for them to present it to the class. The role-play will help reinforce the idea that human actions affect natural cycles and that their own individual actions can make a difference to environmental quality.


Science Inquiry

With the inquiry activity at the following URL, students will construct a scientific model of the carbon cycle to show how matter is continuously transferred within and between organisms and their physical environment.


Real-World Connection

The activity at the URL below will show students how communities can help with carbon sequestration by preventing deforestation of their local forest resources. The activity involves a real-world case study. From the activity, students will learn the importance of forests for carbon sequestration and how sequestration can be used to boost a local economy through the sale of carbon credits.


Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 18.2 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

In this lesson, you read how human actions influence the carbon and nitrogen cycles. Human actions influence many natural processes. The influence may be great. One reason is that there are so many people on the planet. Do you know how many people live in the world today?

Why has the human population grown so large?

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