Required Practical: Decay

• Why does milk sour when left at room temperature?

  Bacteria produce acidic molecules during decay
• What enzyme is used to model decay in the experiment?

  Lipase
• What does the indicator cresol red indicate in the experiment?

  It changes color based on acidity
• What color does cresol red turn in acidic conditions?

  Yellow
• What is the purpose of sodium carbonate in the experiment?

  To create an alkaline environment
• What is the first temperature used in the experiment?

  20 degrees Celsius
• What is the independent variable in this experiment?

  Temperature
• What is the dependent variable in this experiment?

  Time taken for the milk solution to turn yellow
• What are control variables in this experiment?

  Volumes of lipase, milk, sodium carbonate, and cresol red
• Why is it important to use a clean test tube for each experiment?

  To avoid triggering reactions prematurely
• How can the difficulty of timing the color change be reduced?

  By sharing data and calculating a mean
• What happens to enzyme activity at lower temperatures?

  Reactions occur slowly
• What is the optimum temperature for enzyme reactions?

  The temperature at which reactions are fastest
• What happens to enzymes at temperatures higher than the optimum?

  They denature and may stop working
• How do decomposing microorganisms behave in warm conditions?

  They work faster but not in hot conditions
• What are the steps to investigate the effect of temperature on the decay of milk?

  1. Label test tubes for lipase and milk.
  2. Add lipase solution to the lipase test tube.
  3. Add indicator and milk to the milk test tube.
  4. Add sodium carbonate to the milk test tube.
  5. Place both test tubes in a water bath at the chosen temperature.
  6. Transfer lipase to the milk and stir.
  7. Start timing until the solution turns yellow.
  8. Record results and repeat at different temperatures.