Before you plan an experiment it might be useful to list some of what you already know about changes in each of the environmental factors in your aquarium. Discuss each of the questions below in your group and write down some of your ideas. You will be asked to share your thoughts so record your ideas carefully.

• What evidence have you observed that demonstrates that plants consume carbon dioxide?

• What evidence have you observed that demonstrates that animals produce carbon dioxide?

• What evidence have you observed that the day/night cycle affects how plants produce carbon dioxide?

• What do changes in the pH of a solution indicate about the amount of dissolved carbon dioxide in the water?

• If we record the pH of water in an aquarium with a few pieces of Elodea (water plant) and a few goldfish over the course of the day what changes , if any, might we see. Explain your reasoning?

We want to know how the day/night cycle effect the amount of carbon dioxide in an aquarium with plants and fish. We also want to know if any changes in carbon dioxide are due to interaction between changes in light and plants or changes in light and animals. Discuss your ideas about how to set up this investigation.