Required Practical: Effect of Temperature on Respiration in Yeast — AQA GCSE Biology
This required practical investigates how temperature affects the rate of anaerobic respiration (fermentation) in yeast.
The principle
Yeast respires anaerobically (fermentation), producing ethanol and carbon dioxide: glucose → ethanol + carbon dioxide
We measure the rate of respiration by the rate at which carbon dioxide is produced.
Method
- Mix yeast with a glucose solution in a test tube and cover with a layer of oil (to keep out oxygen, ensuring anaerobic conditions).
- Connect to a delivery tube and count the bubbles of CO₂ per minute, or measure the volume of gas collected.
- Place the tube in a water bath at a set temperature.
- Repeat at a range of temperatures (e.g. 10, 20, 30, 40, 50 °C).
Results
- As temperature increases, the rate of respiration increases (enzymes work faster), up to an optimum (around 40 °C).
- Above the optimum, the rate falls sharply because the respiration enzymes denature.
Control variables
Keep the volume and concentration of yeast and glucose the same; only change the temperature.
Exam tips
- The CO₂ production rate measures respiration rate (bubbles/min or gas volume).
- Rate increases to an optimum, then falls because enzymes denature.
- Oil keeps conditions anaerobic.
- Control the amounts of yeast and glucose; vary only temperature.