No questions found
(a) The student noticed that there was a large variation in the results. This may be because it was difficult to know when to stop the stopwatch.
Suggest two problems in deciding when to stop the stopwatch in this investigation.
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(b) The student made a stock cleaning solution containing $1\, \text{mg cm}^{-3}$ of subtilisin A, disodium EDTA and a buffered saline solution. The disodium EDTA and the buffered saline solution were the same concentrations as used in the trials.
This solution was used to make a range of concentrations that could be used to find the concentration of subtilisin A in the contact lens cleaning solution.
(i) Describe how the student could dilute the stock solution to make a range of concentrations to use in their investigation. The student decided to make $50\, \text{cm}^3$ of each concentration.
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(b) (ii) State a solution the student should use as a control. Give a reason for your answer.
control solution ...................................................................
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(c) The student used the apparatus shown in Fig. 1.2 to investigate the effect of different concentrations of subtilisin A on the rate of removal of coloured gelatin from the simulated lenses at $35^{\circ}\text{C}$.
(i) Identify the independent and dependent variables in this investigation.
independent variable ................................................
dependent variable ................................................[2]
(c) (ii) Describe a method the student could use to find the effect of different concentrations of subtilisin A on the removal of protein from the simulated lenses.
Your method should be detailed enough for another person to follow and should not repeat any details from (b) (i) of how to dilute the stock cleaning solution.
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(d) The student plotted a graph of the results.
(i) Complete Fig. 1.3 by adding labels for the axes, including units, and by showing the expected shape of the curve.
[Image: Fig. 1.3]
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(d) (ii) Describe how the student would use this graph to find the actual concentration of subtilisin A in the contact lens cleaning solution.
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538
534
507
(a) Identify the independent variable in this investigation. .........................................................................................................................[1]
(b) (i) What conclusions can be made about the effects of pre-natal alcohol exposure compared to no pre-natal alcohol exposure on the conduction velocity in the median nerve in the sensory neurones and in the motor neurones.
sensory neurones ........................................................................................................................................
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motor neurones .........................................................................................................................................
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(b) (ii) State one other conclusion about conduction velocity in the median nerve that can be made from these results.
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(c) Identify which of the results in Table 2.1 is the most reliable. Give a reason for your answer.
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(d) (i) State why the results for the sensory conduction velocity of the median nerve of group 1 and group 2 at 20 days and 400 days may be significant.
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(ii) There is a difference between the mean conduction speed in sensory neurones in the two groups of babies. State one reason why the t-test is suitable to determine if this difference is significant.
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(iii) State a null hypothesis for this test.
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(e) Suggest two reasons why the results of this investigation may not be valid for all babies born to mothers who drank alcohol while they were pregnant.
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534
511
553
