Fermentation in yeast is used in the manufacture of bread and alcoholic drinks - AQA - GCSE Biology: Combined Science - Question 3 - 2021 - Paper 1

A layer of oil was needed to keep oxygen out of the mixture. This is important because fermentation is an anaerobic process, meaning it occurs without oxygen. The oil prevents oxygen from diffusing into the mixture, allowing the yeast to carry out fermentation effectively.

The mixture was left for 20 minutes before the gas syringe was attached to allow the yeast to acclimate to the temperature of 2 °C. This period also allows the yeast cells to reach a steady state, enabling accurate measurement of gas production once the gas syringe was connected.

At 2 °C, the yeast enzymes were likely too cold to function optimally, resulting in little to no production of carbon dioxide during the initial 30 minutes. Once the flask was moved to 35 °C, the temperature became ideal for enzyme activity, leading to a rapid increase in gas production as the enzymes became active and fermentation accelerated.

For the flask kept at 35 °C, the temperature was within the ideal range for yeast enzymes to function. Consequently, gas production increased steadily from the start. The results indicate that fermentation occurred effectively, with a consistent release of carbon dioxide over time, reflecting optimal conditions for yeast activity.