Paper 1 H - SAMPLE SET 1 Q16
16) A group of students investigate the effect of temperature on the breakdown of the fat in milk by the enzyme lipase.
In their investigation they use an indicator called phenolphthalein.
Phenolphthalein is pink in alkali conditions but becomes colourless when the pH falls below pH 8.
A student puts 5 drops of phenolphthalein and 5 ml of full fat milk in to a test tube.
She adds 1 ml of lipase, stirs the mixture and times how long it takes to lose the pink colour.
Other students repeat this but at different temperatures.
In their investigation they use an indicator called phenolphthalein.
Phenolphthalein is pink in alkali conditions but becomes colourless when the pH falls below pH 8.
A student puts 5 drops of phenolphthalein and 5 ml of full fat milk in to a test tube.
She adds 1 ml of lipase, stirs the mixture and times how long it takes to lose the pink colour.
Other students repeat this but at different temperatures.
The table shows the group’s results.
(a) Explain why the pH falls when lipase breaks down the fat in milk. [2]
(b) Plot a graph of the results and draw a line of best fit. [5]
(b) Plot a graph of the results and draw a line of best fit. [5]
(c) Explain the difference between the results at 20°C and 40°C. [3]
(d) Explain the difference between the results at 80°C and 40°C. [3]
(e) (i) One student says that the results show that the optimum temperature for the lipase is 40°C.
The teacher says that she cannot say for certain that it is 40°C.
Explain why. [1]
(ii) Give two reasons how the students could modify their method to find out the optimum temperature more accurately. [2]
(f) The students rounded their times to the nearest 10 seconds.
They did this because they found it difficult to judge exactly when the pink colour had disappeared.
Describe and explain two ways the method could be improved to give more accurate measurements. [2]
1 ...........................................................................................................................
2 ...........................................................................................................................
(Total for Question 16 = 18 marks)
(d) Explain the difference between the results at 80°C and 40°C. [3]
(e) (i) One student says that the results show that the optimum temperature for the lipase is 40°C.
The teacher says that she cannot say for certain that it is 40°C.
Explain why. [1]
(ii) Give two reasons how the students could modify their method to find out the optimum temperature more accurately. [2]
(f) The students rounded their times to the nearest 10 seconds.
They did this because they found it difficult to judge exactly when the pink colour had disappeared.
Describe and explain two ways the method could be improved to give more accurate measurements. [2]
1 ...........................................................................................................................
2 ...........................................................................................................................
(Total for Question 16 = 18 marks)