Doing a report for an oxygen mass transfer experiment. For background the experiment was performed in the bioreactor and i recorded the dissolves oxygen at different air flows and speeds with just water. After that i added a yeast mixture and recorded dissolved oxygen until steady state again. Can someone please help with the following two questions

Use the data during the no air sparging period to calculate the specific rate of oxygen uptake by the cells. You can get this value through a mass balance on oxygen.

Why was the sulphite added to the solution? Explain using a chemical reaction.