Beacon Lesson Plan Library

I Need Room to Breathe

Joe Brock
Bay District Schools


Students use a ph indicator in a structured inquiry lesson to learn how exercise affects carbon dioxide levels in exhaled air.


The student uses systematic, scientific processes to solve problems and reach conclusions.


-Clear plastic cup
-Plastic drinking straw
-Universal ph solution indicator. This is a chemical that can detect the ph level of solutions when acids or bases are added to soltutions and can be purchased through common scientific catalogs as Fisher, Ward, Boreal, or Flynn.
-Ammonia solution (1 part household ammonia, 7 parts water) and dropper
-Lab Sheet (see associated file)


1. Access the first Website in Weblinks and read about structured inquiry.

2. Access the second Website in wWblinks and read about respiration.

3. Prepare a duplexed information sheet that explains structured inquiry and the respiration process for the students.

4. Prepare two plastic cups of 50ml of water and ammonia solution (use 1 part of household ammonia to 7 parts of water) for each student.

5. Duplicate copies of the lab sheet and questions for each student.


1. (Initiation Phase) Tell the students they are going to engage in a structured activity that is designed to teach them how scientists do experiments. The objective of the activity is to complete an investigation that will solve the following problem. How does exercise affect the amount of carbon dioxide in the air we exhale? Distribute a plastic cup containing 50 ml of water to each student. Place four drops of the universal ph indicator solution into each cup and tell the students to gently stir the water in the cup with the plastic straw.

2. (Exploration Phase) Tell the students to take a normal breath and blow through the straw into the solution. After they have blown through the straw, the students should note on their lab sheets, what color change occurs. Explain to the students, the color change occurs because the carbon dioxide in their exhaled breath combines with the water in the plastic cup to form carbonic acid. Carbonic acid is a weak acid that reacts with the universal ph indicator, which changes from green (neutral) to yellow (acid). Distribute the ammonia dropper bottles and tell the students to put one drop into the cup at a time and to stir the solution. Students must count each drop and continue this process until the solution remains a light green for thirty seconds. Tell the students to record the number of drops on their lab report sheets. Tell the students the ammonia is a base and they are adding just enough drops of the ammonia to neutralize the carbon dioxide in the cups. Instruct the students to write what they think would happen to the amount of carbon dioxide in the blood stream after exercise and to write their idea as a hypothesis on the lab sheets.

3. (Experimentation Phase) Give each student another cup that contains 50 ml of water and tell them to gently stir the water as you add four drops of universal ph indicator. Tell students to choose a partner for the exercise portion of the investigation. One student holds the back of a chair while the partner does step exercises for one minute. As soon as the minute of exercise has expired, the student who completes the exercise takes a normal breath and blows through the straw into the second cup. Allow the partners to switch roles and repeat the exercise procedure. After all students have completed the procedures, instruct them to add the ammonia solution drop by drop until the solution turns light green. Tell the students to record the number of drops in the exercise portion of the data sheets. Use one studentís data chart on an overhead projection sheet to demonstrate how they have used a systematic and scientific process to arrive at a conclusion based on the data collected. Use two samples collected from the student to demonstrate the differences between a high and low concentration of carbon dioxide in solution. Explain how the data is analyzed to arrive at a conclusion.

4. (Presentation Phase) Once experiments have been completed, students are instructed to discuss the results and derive a conclusion based on their findings. Students use the remaining class time to complete the questions on the lab sheet and return to the teacher at the end of class. Formatively assess the complete questions and conclusions for discussion the next day.

5. The next day, prepare an overhead projection sheet of the data chart with data inserted into the chart. Discuss with students why the color changes occur and how these color changes indicate the differences in the amount of carbon dioxide produced in exhaled air. Also discuss how students should develop their conclusions based on the data they have collected and the correct answers to the follow up questions. Collect the lab reports and check for corrections students make on their reports.


Students are assessed at the end of the investigation through their conclusions and completed questions, to determine the level of competency attained. The level of mastery is ascertained by the number of correct answers on the final questions and through the accuracy of the conclusion.


The lesson can be extended by a allowing students to investigate different conditions that may influence the amount of carbon dioxide in the blood stream, for instance, if they held their breath, or if there is a difference between adults and children.

Web Links

This Weblink describes the inquiry continuum and how structured inquiry fits into the teaching of science.
Science Through Design

An excellent description of respiration and gas exchange can be found at this site. Site contains graphics and may take a moment to load. (Site active 7/29/03)
Human Physiology

Attached Files

Gas Exchange Lab Sheet†††††File Extension: pdf

Return to the Beacon Lesson Plan Library.