Breathing and Holding Your Breath

In the lab, Breathing and Holding Your Breath, students begin with interactive activities to develop a basic understanding of why cells need oxygen and need to get rid of carbon dioxide, how the circulatory and respiratory systems cooperate to bring oxygen and remove carbon dioxide from cells all over the body, and how the nervous system regulates breathing. Then, students carry out an experiment to test whether changing levels of oxygen and carbon dioxide influence how long they can hold their breath. 

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

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, useful preparatory or follow-up activities, additional resources or any questions you have related to the activity, or a brief description of any problem you might have encountered. If you have a relevant Word document you would like to have posted on this comments page, such as a version of the protocol you have used in your classroom, or 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:



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.

Post new comment
