A group of students wants to determine whether a gas is released when glucose is added to a solution of living yeast cells and water. Their experimental setup is shown below.

The students add glucose to a mixture of yeast and water in Flask A. If a gas is released, the test solution in Flask B will turn yellow. The students observe and record the appearance of Flask B at the beginning of the experiment, and again after 24 hours.

• Explain the importance of using a control in the experiment.
• Describe a control for this experiment. Be sure to include the specific parts of the setup.
• Compare the control to the original experimental setup.

Write your answer in your Answer Book.