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Practical skills assessed in a written examination

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Question 34

A student investigated the effect of ethanol concentration on the permeability of beetroot (Beta vulgaris) cell membranes. This was the method used:

  • Use a cork borer to cut 15 cylinders of beetroot.
  • Slice these cylinders into discs approximately 2 mm thick using a scalpel.
  • Rinse the discs under running tap water for 5 minutes, then pat them dry with a paper towel.
  • Place 10 beetroot discs into each of 5 test tubes.
  • Add 10 cm3 of different concentrations of ethanol (0%, 15%, 30%, 45%, and 60%) to the respective test tubes.
  • Leave the test tubes on a laboratory bench at room temperature for 25 minutes.
  • Shake each tube vigorously once by hand, then pour the liquid into a cuvette.
  • Use a colorimeter to measure the light absorbance of each solution.

Identify two limitations of the student's method. For each limitation, explain how it limits the validity of conclusions that can be drawn, and suggest an improvement that would increase the validity of the conclusions.

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Practical skills assessed in a written examination Questions

  1. A Level
  2. /Biology
  3. /Practical skills assessed in a written examination