1. Action of urease Objectives
To look at the action of an enzyme in different temperatures
Learn to identify an end point
Plan to record results effectively
Start to learn skills of analysis and evaluation of results

2. Background facts
Urea is broken down very slowly over time to ammonia and carbon dioxide;
This process is much more rapid in the presence of urease
Ammonia dissolved in water is an alkali
Urea dissolved in water is neutral
So the action of urease can be observed by the change in pH of the solution
A change in pH can be shown by the presence of an indicator called Phenolphthalein which goes pink in solutions of pH 9 or above.

3. Practical
Each group will investigate a different temperature: 10C, 20C, 30C, 40C, 50C
Each group will replicate their experiment three times
The end point will be the colour change
Each group must record the time from adding the soy bean extract till the colour change is observed.

4. Equipment
20 ml 10% solution of fertiliser urea (a solid fertiliser made of pure urea)
10 ml soya bean extract, prepared as described below (from 1 g of dried soya beans)
10 ml distilled water
Pasteur pipettes for transferring the solutions
3 test tubes and a test tube rack.
Phenolphthalein indicator
Thermometer
250ml beaker of water, bunsen burner and tripod

5. Preparation of urease – done for you!
Soak the soya beans in water for at least 1 h (preferably overnight).
Blend the soaked soya beans in a food blender with about 10 ml of water per gram of dry soya (the water from soaking the beans can be used) until the mixture is smooth (for about 5 min).
Filter the soya purée through filter paper in a funnel.
Collect and keep the filtrate, which contains urease.

6. Method Add 2 ml of indicator to each of three fresh tubes.
Place in beaker of water heated to desired temperature. Put tube of soy solution in as well to warm it to correct temperature
Mix 2 ml of urea solution into each of the three tubes. Note the colour. Leave for a couple of minutes
Add 2 ml of the soya suspension to one.
Start timing instantly. Note time of colour change and which tubes change.
You need to repeat this with each of the three tubes. I advise you check the temperature and reheat to correct temperature in between tests.

7. Results
Work out how to record your results – draw up your own results table
Collect class results
(10 marks given for table of results)

8. Questions 1. Why was it important to replicate the results?
2. Name two variables that were controlled to ensure a fair test
3. Plot the class results on a line graph (6 marks)
4. Explain the class results using Q10 and lock and key theory in your explanation
5. If class results don’t fit these explanations explain why and suggest reasons for the experiment not to have worked.
20 marks