Today students participated in activity #17 Gas Exchange. We started by defining gas exchange, respiration, and indicator. Next students learned about the indicator BTB and how blue represented oxygen and how yellow represented carbon dioxide. Then student each had a plastic bag and straw. In the plastic bag students put water and BTB. Next students blew into the straw and noticed that it changed to yellow. They then added NaOH to turn back to blue. They count the number of drops and recorded their data. We finally made a graph. of the results. This showed how we breath in oxygen and exhale carbon dioxide.