Required Practical: Decay (OCR GCSE Biology A (Gateway Science Suite)): Revision Notes
📚 Revision Notes
7.2.5 Required Practical: Decay
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Aim: This practical investigates how temperature affects the rate of decomposition by observing the pH change in fresh milk as it breaks down with the help of the enzyme lipase. This experiment simulates the process of decomposition, allowing us to understand how environmental conditions influence the speed at which organic material decays.
Investigating the Effect of Temperature on Decomposition
You will study how temperature affects decomposition by monitoring the breakdown of fats in milk, which causes a change in pH. This change can be tracked using an indicator called phenolphthalein.
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Practical Steps:
- Prepare a Solution:
- Mix fresh milk with phenolphthalein, which will act as a pH indicator.
- The solution will initially be pink in colour, indicating an alkaline environment.
- Alkalize the Solution:
- Add sodium carbonate to the milk and phenolphthalein mixture. Sodium carbonate is alkaline, so it turns the solution pink by raising the pH.
- Temperature Control:
- Place the test tube containing the solution in a water bath set to a specific temperature. This controls the environment in which the decomposition reaction occurs.
- Start the Reaction:
- Add lipase enzyme to the solution. Lipase breaks down fats in the milk, producing fatty acids that lower the pH of the solution.
- Observe the Reaction:
- Begin timing as soon as the lipase is added.
- Monitor the solution and measure the time it takes for the pink colour to disappear. The disappearance of the pink colour indicates that the solution has become acidic due to the decomposition of fats, signifying a drop in pH.
- Repeat:
- Conduct the experiment at different temperatures to determine which temperature leads to the fastest disappearance of the pink colour. This temperature corresponds to the highest rate of decomposition.
Key Points to Consider:
- Temperature's Role: Enzymes like lipase work more efficiently at certain temperatures. Typically, the rate of decomposition increases with temperature until the enzyme's optimum temperature is reached. Beyond this point, the enzyme may denature, slowing down or halting the decomposition process.
- Controlled Variables: Ensure that the concentration of lipase, the volume of milk, and the amount of sodium carbonate remain constant throughout the experiment to ensure accurate and comparable results.
Applications of the Practical:
Understanding how temperature affects decomposition is crucial in fields like agriculture, waste management, and food preservation, where controlling the rate of decay is essential.