Answer the following questions on paper:

• How do the initial pH values for the water, fish only, Elodea only, and fish and Elodea aquarium compare?

• How did the pH vary as the light decreased around your aquarium? As the light decreased, what happened to the pH?

• How do the changes in pH values during the day/night cycle compare in each of the different aquarium set-ups?

• Based on the data your class has collected in each aquarium, what ideas do you have about how light and carbon dioxide production are related? What role do plants play in the process? What role do goldfish play in the process?