The F.A.C.E. Method As botanists and ecologists became increasingly aware of the increase in atmospheric carbon dioxide due to humans burning fossil fuels, they began to wonder if this change could affect plant growth. The Free-air Carbon dioxide Enrichment (F.A.C.E.) A method was designed to test this. The method uses a series of pipes to regularly release small amounts of carbon dioxide into an enclosed area where a crop such as rice or wheat was growing. Scientists would record the yield of each crop after an entire growing season and compare it to another plot where the plants were exposed to normal air. Each plot of growing area received the same amount of sunlight, fertilizer, and water. Overall, scientists measured a 5-8% increase in yield in the CO2-enriched plots compared to the other ones. What independent variable were the scientists studying in this case? What dependent variable were the scientists measuring? What was the experimental group in their study? What was the control group? When an experiment is designed, all variables between the experimental group and control group must be held constant. What were the constant variables in these experiments