Practicalassessment
Biology TASK 1 DETERMINING THE CONCENTRATION OF GLUCOSE It is often important to measure the concentration of glucose in a solution. Diabetes mellitus
is a condition where blood sugar level is not controlled correctly and affected people take
insulin to help to control their glucose levels and test their blood to determine the level of
glucose in it.There are a variety of different ways in which blood glucose level can be
measured.
In this experiment you will test the glucose concentration in a variety of solutions of known
value and you will draw a graph to show your results. This type of graph is known as a
Standard Curve. You will then use this graph to estimate the glucose concentration in an
unknown solution. This is the method which was used in hospital labs to measure the
glucose level in blood samples.
Glucose (C6H12O6) is a monosaccharide reducing sugar. In this reaction the glucose readily
donates electrons which are accepted by the permanganate causing it to change colour.
You will be measuring the time taken for the pink colour of the potassium permanganate to
disappear once the glucose solution has been added.
Instructions
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Label 3 beakers: - S for Sulphuric acid, PP for pottassium permanganate, G for
glucose.
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Label your syringes in the same way.
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Add about 25 cm3 of sulphuric acid and potassium permanganate to the beakers – this will be
your stock to use throughout the experiment. Note which glucose solution you are testing
first.
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Use the syringe labelled glucose to place 10 cm3 of the first glucose solution in to the boiling
tube.
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Add 5 cm3 of sulphuric acid.
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Add 2 cm3 of potassium permanganate and start the clock.
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Stir with a stirring rod and stop the clock as soon as the pink colour disappears.
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Record the time and the glucose solution used.
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Rinse the syringe you used for the glucose solution.
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Repeat using the other glucose solutions of known concentration.
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Repeat for the glucose solution in the bottle labelled G-X
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Record your results
(i) Plot a graph of glucose concentration against time to clear on graph paper and use this to
estimate the concentration of the unknown solution which you tested.
(ii) Now plot a graph showing 1/t against concentration of glucose
(iii) Describe any trend you see in your graphs
(iv) Describe what you have found out about the concentration of the unknown solutions and
show it clearly on the appropriate graph
(v) Comment on your results, their accuracy, and the likely sources of error in the experiment.
Consider the limitations of the experiment, and possible improvements to it.
TASK 2: COLLECTING AND ANALZYING DATA ABOUT ENZYMES ACTIVITY. Disaccharides are chemically changed to simple sugar molecules by enzymes. In this task, you will
determine whether a certain enzyme is specific for only one disaccharide.
Directions
After reading the directions, set up a rough copy of a data table to record your observations.

Add two drops of the known glucose solution to Well 1 of the spot plate. Insert the end of one
strip of the glucose test strip indicator. Wait 15-30 seconds before reading the results. Record
your observations.

Add one drop of the enzyme solution to Well 2 of the spot plate. Repeat the above test with
the test strips and record your observations.

Add two drops of each of the unknown disaccharide solutions to the spot plate as follows:
A in spot 3, B in spot 4, C in spot 5
Test each with a different indicator strip. Record your observations.

Add two drops of each of the unknown disaccharide solutions to the spot plate as follows:
A in spot 6, B in spot 7, C in spot 8
To each sample of unknown disaccharide, add one drop of the enzyme. Wait about two
minutes and then test with the indicator strip. Record your observations.
In the space below, draw an appropriate table to record your observations.
(i) Using complete sentences, explain why testing well 2 is a necessary step in the procedure.
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(ii) Explain in complete sentences, how this experiment shows that enzymes are specific for only
one substrate?
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(iii) If the enzyme used in this experiment was lactase, name the specific substrate on which it
acts.
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