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Food Webs, Energy Flow, Carbon Cycle, and Trophic Pyramids

Food web with plants and animals

To begin this hands-on, minds-on activity, students view a video about ecosystem changes that resulted when wolves were reintroduced to Yellowstone. Then, students learn about food chains and food webs, and they construct and analyze a food web for Yellowstone National Park. Students use what they have learned to understand trophic cascades caused by the return of wolves to Yellowstone.

Next, students learn that the biosphere requires a continuous inflow of energy, but does not need an inflow of carbon atoms. To understand why, students analyze how the carbon cycle and energy flow through ecosystems result from photosynthesis, biosynthesis, cellular respiration, and the trophic relationships in food webs.

In the final section, students use the concepts they have learned to understand trophic pyramids and phenomena such as the relative population sizes for wolves vs. elk in Yellowstone. Thus, students learn how important ecological phenomena result from processes at the molecular, cellular, and organismal levels.

For virtual instruction, you can use Food Webs – Understanding What Happened When Wolves Returned to Yellowstone, Carbon Cycles and Energy Flow through Ecosystems and the Biosphere, and Trophic Pyramids

This activity is aligned with the Next Generation Science Standards (NGSS).

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

Please note that Word files display differently on different computers, so you will want to use the PDF files to see the correct formatting of the Student Handout and the images for the cards for the food web in the Teacher Preparation Notes. The first file attached below is suitable for professional printing and cutting of the cards for the food web part of the activity. The second and third attached files provide an alternative, smaller deck of cards, which you can use if you prefer a somewhat briefer, simpler food web activity.

We invite comments on this Hands-On Activity and the accompanying Teacher Preparation Notes. If you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at

See also a complete list of activities: Minds-on Activities for Teaching Biology

Yellowstone cards.pdf889.17 KB
Yellowstone cards smaller deck.docx2.88 MB
Yellowstone cards smaller deck 2019.pdf4.52 MB


iwaldron's picture

2021 revision

We have revised the Student Handout to improve clarity and the logical progression of student understanding.

GIna Visitor's picture


Video is no longer available

iwaldron's picture

Video available

I am puzzled by your comment, since I found the video at Please try again.

 Thank you,


iwaldron's picture

March 2019 revision

Based on helpful input from Philadelphia area teachers, the procedure in the Student Handout has been clarified to make it easier for students to construct an accurate food web. Some of the explanations and questions have been revised to improve student understanding.


iwaldron's picture

2019 revision

The Student Handout has been reorganized and streamlined to teach the concepts more effectively. Each section begins with a phenomenon to stimulate student engagement and thinking. Many of the questions, figures and explanations have been revised for greater clarity.

Vignesh's picture


I just need to review the answer

iwaldron's picture

Answer key

Please see the Teacher Preparation Notes for information about the answer key and other useful information.

Ingrid Waldron

iwaldron's picture

2016 Revision

In this revision we have improved the accuracy of the descriptions of chemical energy and energy metabolism in the Student Handout and Teacher Preparation Notes. In addition, we have made available an alternative version of the deck of cards for the Yellowstone food web part of the activity for teachers who want a somewhat briefer, simpler food web activity.

Josh Higgins's picture

Answer Key

Where can I find the answer key?

iwaldron's picture

Answer key

Please see the Teacher Preparation Notes which include learning goals, instructional suggestions, and background biology, as well as instructions about how to get the key.

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