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Negative Feedback, Homeostasis, and Positive Feedback – Examples and Concepts

This minds-on, hands-on activity begins with an anchoring phenomenon, how a person’s breathing changes when he/she is re-breathing the air in a plastic bag. Students develop a negative feedback model of how the changes in breathing stabilize blood levels of O2 and CO2. To understand changes in breathing when running, students analyze cellular respiration.

Next, students use a negative feedback model to understand temperature regulation and homeostasis. Then, students analyze how failures of negative feedback can result in diabetes. Finally, students compare and contrast positive and negative feedback.

The Appendix for the Teacher Preparation Notes suggests an optional activity in which each student group investigates a question or hypothesis concerning negative feedback, homeostasis and changes in breathing.

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

The Teacher Preparation Notes provide instructional suggestions and background information and explain how the activity is aligned with the Next Generation Science Standards.

We invite comments on this Hands-On Activity and the accompanying Teacher Preparation Notes, including suggestions for other teachers who are planning to use the activity, any questions you have related to the activity, or a brief description of any problem you might have encountered. If you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at


iwaldron's picture

2023 revision

We have reorganized the Student Handout to begin with the phenomenon of deeper and faster breathing as students re-breathe the air in a plastic bag and then explore an explanation for this and related phenomena. We have also added a section on diabetes which will help the students appreciate the practical significance of understanding negative feedback. We have also revised multiple explanations and questions to improve the clarity of the Student Handout. To accommodate these revisions, we have totally revised the Teacher Preparation Notes.

iwaldron's picture

2019 revision

I have reorganized the sections of the Student Handout on negative feedback and changes in breathing to begin with an anchor phenomenon and have students work to figure out an explanation of this anchor phenomenon. I have also streamlined the Student Handout and made multiple revisions to improve clarity.


iwaldron's picture

2018 revision

The Student Handout has been substantially revised to clarify the concepts and improve student understanding.

iwaldron's picture

Video which Demonstrates Experimental Technique

We have prepared a video to demonstrate the procedure for the first experiment and help your students get more reliable results. The video available at demonstrates how to prepare the bag and breathe into the bag. You will want to view this video and then either demonstrate the procedure for your students or have them watch this video. Helpful advice includes:

  • To begin, the bag should be opened completely and swished through the air to fill it.
  • Make sure to have a tight seal between the bag and the person’s face so no air is leaking in and out of the bag.
  • Maintain a tight seal throughout the entire test interval (3 minutes for developing the procedure for evaluating depth of breathing and 4 minutes for the actual experiment).
  • Each subject should stand while breathing into the bag to make it easier for observers to see the whole bag to evaluate the breathing rate and depth and also to standardize posture for different subjects
iwaldron's picture

November 2015 revision

This revision includes improved instructions for the experimental methods, some clarification of explanations and questions, and additional biological information which will help with the interpretation of the experimental results.

iwaldron's picture

2015 Revision

This 2015 activity, "Homeostasis and Negative Feedback – Concepts and Breathing Experiments", is essentially a new activity with a minor overlap with the previous breathing activity. This 2015 activity includes:

  • an introduction to homeostasis and negative feedback
  • an experiment that demonstrates the effects of negative feedback on rate and depth of breathing
  • an added section in which students design and carry out an experiment to test a hypothesis concerning the effects of exercise on rate and depth of breathing.

This activity is aligned with the Next Generation Science Standards (see page 1 of the Teacher Preparation Notes).

Serendip Visitor's picture

filling the 13 gallon bag results/data interpretation

Could you explain what results should come from this part of the lab exercise?
I would predict a shorter time than after normal breathing but why?

iwaldron's picture

regulation of breathing

As indicated by the questions on the top part of page 5 of the Student Handout, breathing into the bag results in increased concentration of CO2 in the bag and decreased concentration of O2. This in turn results in increased concentrations of CO2 and decreased concentration of O2 in the blood and in the brain. The length of time you can hold your breath decreases as a result of these changes. If you carry out the Additional Activity described on page 2 of the Teacher Preparation Notes, the results will demonstrate that the brain is responding specifically to changes in CO2 levels, not O2 levels. In fact, it is the increased concentration of H+ (which is generated when CO2 combines with H2O in the blood to form carbonic acid) which stimulates the brain to resume or increase breathing.

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