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

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.

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.

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

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.

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.

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

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