Required Practical 1

Question 1

What is the method

Answer 1

1) using a marker pen write an “X” about half way down one side of each 5 test tubes
2) also label each of these tubes with one of the 5 different phs you will be investigating
3) label each of the 5 remaining tubes with one of the 5 phs you will be investigating

Question 2

Method (2)

Answer 2

4) add 10 cm3 of the solution of milk powder to each of the 5 tubes marked with an X
5) in the tube not marked with an X and labelled pH 5 add 2 cm3 of trypsin solution to 2cm3 of pH 5 buffer
6) repeat step 5 with the buffer solutions at pH 6,7,8 and 8.5 in the 4 remaining test tubes not marked with an X. Rinse your pippete with distilled water between each buffer

Question 3

Method (3)

Answer 3

7) stand the 5 test tubes containing the solution of milk powder and the 5 test tubes containing the trypsin and buffer in a water bath at 37 degrees
8) leave all 10 tubes in the water baths for a suitable amount of time
9) add the trypsin and pH 5 buffer solution mixture to the corresponding tube containing milk powder solution. Start the stopwatch and mix thoroughly by stoppering each tube with a rubber bung and and inverting several times

Question 4

Method (4)

Answer 4

10) return the tube to the water bath at 37 degrees Celsius
11) repeat steps 9 and 10 for the other pHs noting the time at which each experiment is started
12) time how long it takes the milk to go clear by measuring the time taken to first see the “X” through the solution

Question 5

Method (5)

Answer 5

13) record the time for each of the 5 experiments
14) share your data with other members of the class record these in your table and process the data accordingly

Question 6

Explain why you were asked to collect the class data

Answer 6

To calculate a more reliable mean and reduce the effect of anomalies

Question 7

Is pH 7 the optimum pH for trypsin and what further investigations can you conduct to find out

Answer 7

You can’t be sure as intermediate values could have a higher rate of reaction so you need to test intermediate valves then test in smaller increment between the fastest rate of reaction

Question 8

How did you decide what was a suitable length of time to leave your tubes in the water baths before mixing

Answer 8

Until the test tubes reached 37 degrees Celsius

Question 9

Describe what you did during the investigation to minimise the effect of temperature changes

Answer 9

We returned the test tubes to 37 degree and when the temperature reached lowed we added hot water to increase the temperature
And measured the temperature at regular intervals

Question 10

Give 2 ways in which the method could be improved

Answer 10

Use of electronic water bath to maintain the temperature at 37 degrees
Stir the tubes throughout the reaction
Not enough intermediate pH values were tested to accurately identify the optimum

Question 11

Was the data collected quantitative or qualitative

Answer 11

Quantitative becuase it was numerical data that was collected in a table

Question 12

Another student carried out the same investigation as you but used a timer that measured to 0.01 of a second. His results wouldn’t be any more accurate than yours. Suggest why

Answer 12

The end point is subjective and it takes time to start stop or read the time between 0.01 seconds

Question 13

What is meant by hydrolysed

Answer 13

The peptide bonds between the milk protein and trypsin is broken down