During the Krebs Cycle 1. hydrogen ions and oxygen form water
2. the cell releases a small amount of energy through fermentation
3. each glucose molecule is broken down into 2 molecules of pyruvic acid
4. pyruvic acid is broken down into carbon dioxide in a series of reactions

The answer to this will be from your lab notes/procedure. it would be best to ask another student who participated in the lab as we do not know what was done, what enzyme or if the temperature is celsius or fahrenheit. if i were to guess though i'd say the rate stopped due to enzyme denturing at high temperature