To ensure that any temperature change Sofia measures is solely due to yeast respiration, she needs to include a control group in her experiment. The control group should be identical to the experimental group in all aspects except for the presence of yeast.
By having a control group without yeast, Sofia can compare the temperature changes observed in the experimental group (with yeast) to those in the control group. Any temperature change observed in the control group would indicate that it is not solely due to yeast respiration but might be influenced by other factors.
Including a control group helps Sofia isolate and identify the specific contribution of yeast respiration to the temperature changes she measures. It allows her to differentiate between the effects of yeast respiration and any external factors that might influence temperature, thus providing more reliable and accurate results.