HBI6X/PM1. General Certificate of Education Advanced Level Examination June Unit 6X A2 Externally Marked Practical Assignment Task Sheet 1

Transcription

1 Centre Number Surname Candidate Number For Examinerʼs Use Tota Task 1 Other Names Candidate Signature Genera Certificate of Education Advanced Leve Examination June 2010 Human Bioogy HBI6X/PM1 Unit 6X A2 Externay Marked Practica Assignment Task Sheet 1 To be competed before Task Sheet 2 For submission by 15 May 2010 For this paper you must have: a ruer with miimetre measurements a cacuator. HBI6X/PM1

2 2 The use of the enzyme urease by bacteria in the stomach Introduction Some species of bacteria cause diseases of the stomach. Most bacteria are kied by acidic gastric juice. Gastric juice is produced by the stomach ining. Some species of bacteria survive the antibacteria action of gastric juice by secreting the enzyme urease. This enzyme catayses a reaction that produces ammonia. The ammonia neutraises the acid in gastric juice. Pheno red is a ph indicator that turns from yeow in acidic conditions to pink-red in akaine conditions. Task 1 Finding a suitabe concentration of urease to use In this task, you wi find the concentration of urease that produces a resut in a suitabe time so that you can use this in Task 2. Materias You are provided with pheno red soution 5% urease soution 1% urea soution hydrochoric acid distied water a arge beaker that you can use as a water bath, or access to a thermostatic water bath thermometer sma beakers test tubes test-tube rack timer graduated pipettes or syringes dropping pipettes marker pen. You may ask your teacher for any other apparatus you require.

3 3 Outine method Read these instructions carefuy before you start your investigation. 1. Set up a water bath at room temperature. 2. Labe six test tubes A to F. 3. Put 1 cm 3 5% urease in tube A. 4. Use the 5% urease soution and distied water to make urease soutions of concentrations 4%, 3%, 2% and 1%. 5. Set up tubes B to F. Tube B shoud contain 1 cm 3 4% urease soution. Tube C shoud contain 1 cm 3 3% urease soution. Tube D shoud contain 1 cm 3 2% urease soution. Tube E shoud contain 1 cm 3 1% urease soution. Tube F shoud contain 1 cm 3 distied water. 6. Pace tubes A to F in the water bath. 7. Labe another six test tubes 1 to Add 5 cm 3 urea soution to each tube. 9. Add 2 drops of pheno red and 1 drop of hydrochoric acid to each of tubes 1 to 6 and pace a six tubes in the water bath. 10.After a suitabe time, add the contents of tube 1 to tube A, quicky mix the contents and start the timer. 11.In the tabe beow, record how ong it takes for the pheno red to turn from yeow to pink-red. 12.Repeat steps 10 and 11 but add the contents of tube 2 to tube B, then tube 3 to tube C, then tube 4 to tube D, then tube 5 to tube E and finay tube 6 to tube F. 13.Tube F wi act as a contro experiment. You wi need to decide for yoursef how to make the different concentrations of urease soution how ong to eave the test tubes in the water bath before mixing when the coour change has occurred. Recording your resuts Record your resuts in the tabe. Tube Percentage concentration of urease A 5 Time taken for pheno red to turn pink-red / seconds B 4 C 3 D 2 E 1 F 0 Turn over

4 4 Questions on Task 1 Answer a questions in the spaces provided. 1 Compete the headings on the tabe and the empty es to show how you made the different concentrations of urease soution. Percentage concentration of urease soution Voume of water /... Voume of 5% urease soution /... (2 marks) 2 Urease catayses the reaction urea + water ammonia + carbon dioxide What name is given to the type of reaction that urease catayses? 3(a) You eft tube 1 and tube A for a time in the water bath before mixing their contents. Expain why. 3(b) You were tod to pace the test tubes in a water bath at room temperature. Do you think it was necessary to use a water bath? Expain your answer.

5 5 3(c) Describe how you monitored the temperature of the water bath. 4 What was the purpose of using tube F as a contro? 5 Use your data to suggest the urease concentration that you wi use in Task 2. Expain why you chose this concentration. 6 ph is a factor that affects enzyme activity. Do you think a buffer soution shoud have been added to the contents of the tubes before mixing? Expain your answer. (2 marks) END OF TASK 1 10

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