1. Required Practical 10: Define the term DECAY:
What is the role of phenolphthalein?
Method
Diagram
5cm3 of milk in a test tube
5cm3 of lipase in a tube
Add 5 drops of phenolphthalein indicator to the milk
Add alkaline sodium carbonate to the milk tube. It turns pink.
Put both tubes into a 30oC water bath. Use a thermometer.
Once both tubes are at 30oc, mix them together and start a stopwatch.
Time how long it takes for the tube to lose its pink colour (when lipase has digested the lipids in the milk)
Repeat for a range of different temperatures. 5 4
Factor that effects rate of decay
Explain why
Temperature
Oxygen Availability
Water Availability
Number of decay organisms 8 5 6
Required Practical 10:
The effect of temperature on the rate of decay of fresh milk
Explain how microorganisms decay:
How would you calculate rate? 7
Units? 7
Complete the following word equation:
LIPIDS + LIPASE  ____________ + ___________ 5
Why do you put both separate tubes into water bath for a while before mixing?
Why do you make the milk alkaline?
Explain why the milk loses it’s pink colour.
Explain why you can use pH to measure the rate of decay in milk? 7 8