Based on the data collected, what must be added to the yeast in the test tube in order to facilitate fermentation?

an organic substrate (such as starch)

The complete question is:

Ms. Green's biology students were studying cellular respiration. One simple organism, yeast, can be used to test the rate of fermentation using different variables. Each group mixed 2 grams of yeast with warm water and placed the mixture into one of five test tubes. The variables can be seen on the graph of student data. Test tube five held only yeast and warm water. The groups used the height of the carbon dioxide bubbles produced in a test tube to determine which group had the highest rate of fermentation. Based on the data collected, what must be added to the yeast in the test tube in order to facilitate fermentation?

Answer: Glucose or food source

Explanation: The food source of the yeast is glucose which is required by them to perform the process of fermentation.

The process of fermentation can be defined as the metabolic process that leads to chemical changes in the organic substrate by the action of the enzymes.

The substrate on which the yeast acts should be organic substrate like glucose et cetera.

The yeast derives energy from the sugar present as substrate in the absence of respiration.