Topic 2 Core Practicals

1.	Investigate the effect of enzyme and substrate concentrations on the initial rates of reactions.
2.	Microbiology practical
3.	Investigate membrane structure, including the effect of alcohol concentration or temperature on membrane permeability.
4.	Investigate membrane structure, including the effect of alcohol concentration or temperature on membrane permeability.

Questions

Q1.
 
Catalase is an enzyme present in many tissues of most living organisms. Its role is to break hydrogen peroxide down into oxygen and water. Hydrogen peroxide is produced by cells and is very harmful if it is not broken down.
(a) A study compared the activity of catalase in the tissues of freshwater mussels. Mussels from two different rivers: mussel E from the river Eo and mussel M from the river Masma were studied.
The catalase activity was measured in three tissues, X, Y and Z, taken from each type of mussel.
The graph below shows the results of this study.

(i) Use the information in the graph to state the conclusions that can be made about the activity of catalase in the tissues of
     mussel E.
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(ii) Using the information in the graph, compare the activity of catalase in mussel E and mussel M.
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(b) Catalase activity in tissue from mussels can be studied using the apparatus shown below.
Tissue from mussels is placed in the flask and hydrogen peroxide is added using the syringe. The oxygen produced from the breakdown of hydrogen peroxide is collected in the measuring cylinder.

Describe how this apparatus could be used to compare the catalase activity in two different types of mussel.
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(Total for question = 9 marks)

Q2.
 
Lysozyme is an enzyme found in tears. Lysozyme can destroy some bacteria by 
breaking down the polysaccharide chains that form part of their cell walls.
The graph below shows the effect of increasing the concentration of lysozyme on 
the initial rate of destruction of bacteria.

(i)  Using the information in the graph, explain the effect of the concentration of 
      lysozyme on the initial rate of destruction of bacteria.
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(ii)  Suggest why some of the data points in the graph do not fit on a straight line.
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Q3.
 
The cell vacuoles of beetroot (Beta vulgaris) contain the red pigment betalain.
A student investigated the effect of temperature on the permeability of beetroot cell membranes.
In this investigation, five pieces of beetroot were used. One piece of beetroot was left in 10 cm3 of distilled water for
20 minutes at 20 °C.
After 20 minutes, the piece of beetroot was removed and the intensity of the colour of the water was measured using a colorimeter.
This was repeated with the other pieces of beetroot using water temperatures of 40 °C, 60 °C, 80 °C and 90 °C.
(a)  The student's results are shown in the graph below.

(i)  Using the information in the graph, describe the effect of temperature on the permeability of the cell membranes.
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(ii)  Using the information in the graph and your knowledge of membrane structure, explain the effect of temperature on the cell membranes.
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*(b)  Using all the information given in the question, describe how this investigation could be carried out to provide valid and reliable results.
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(Total for question = 10 marks)

Q4.
 
The cell vacuoles of beetroot (Beta vulgaris) contain the red pigment betalain.
A student investigated the effect of ethanol on the permeability of beetroot cell membranes. 
In this investigation, 10 identical pieces were cut from one beetroot. One piece of beetroot was left in
10 cm3 of 30% ethanol for 20 minutes at 20 °C.
After 20 minutes, the piece of beetroot was removed and the intensity of the colour of the ethanol solution was measured using a colorimeter.
This was repeated with other pieces of beetroot that were left in ethanol concentrations of 0%, 50%, 70% and 100%, at 20 °C.
The student repeated this investigation with the other five pieces of beetroot at the same temperature of 20 °C. The graph below shows the results of these investigations.

(a)  Using the information in the graph, describe the effect of ethanol concentration on the intensity of colour.
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(b)  Using the information in the graph and your knowledge of membrane structure, explain the effect of ethanol on the permeability of beetroot cell membranes.
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(c)  Suggest why the results for these two investigations are different.
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(Total for question = 9 marks)

Mark Scheme

Q1.

Q2
.

Q3.

Q4.