GCSE Biology Required Practical: Decay of Organic Material

Key Stage 4

Meaning

Investigate the effect of temperature on the decay rate of organic material.

Method

• Independent Variable - Temperature of organic material.
• Dependent Variable - pH of milk.
• Control Variables - Volume of milk, volume of indicator solution.

1. Fill a 500ml beaker with 250ml of hot water which will act as a water bath.
2. Place 5cm³ of lipase into a testube using a pipette.
3. Place 5cm³ of milk into another test tube using a pippette with 5 drops of 'Cresol Red' solution.
4. Add 7cm³ of sodium carbonate solution to the milk in the test tube.
5. Place both test tubes in the water back and a thermometer into the milk test tube.
6. Once the milk mixture has reached the temperature of the water bath add 1cm³ of lipase to the mixture and start a timer.
7. Stir throughout then record the time taken for the for the solution to turn yellow.
8. Repeat this using different temperatures of water in the beaker.