Practical questions

You will complete a number of specified practical activities. You could be asked questions about the methods, safety precautions you might take, results and conclusions of these experiments.

Sample question 1 - Foundation

Question

A student investigated the effects of osmosis in potato tissue by placing potato cylinders in different concentrations of sugar solution. The student measured the percentage change of the potato tissue mass depending on the solution strength.

Their results are shown below:

Experiment123456789
Low concentration+4+5+4+6+5+6+5+6+6
High concentration-12-13-15-11-16-2-15-17-15

a) Identify the anomalous result. [1 mark]

b) Calculate the mean change in mass for each concentration. Do not include the anomalous result from Experiment 6 in your calculations

Give your answer to one decimal place. [2 marks]

c) Explain why the student expressed change in mass as a percentage. [3 marks]

This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.

a) Experiment 6, high concentration of sugar. [1]

b)

  • low concentration, 5.2 [1]
  • high concentration, -14.3 [1]

c) The mass of the potato cylinders would be different [1]. Because of this, the results of the experiments for cylinders in low and high concentrations could not be compared [1]. Apparent differences in mass could be as much the result of differences in the initial masses as the effects of osmosis [1].

Sample question 2 - Higher

Question

An investigation was carried out to find the effect of surface area to volume ratio on the rate of absorption in plants.

Cubes of potato were cut to the following sizes:

Investigation to find the effect of surface area on the rate of absorption in plants

The cubes were carefully blotted dry, weighed and their masses recorded.

One cube, 2 cm × 2 cm × 2 cm, was put into a beaker and completely covered with distilled water.

Eight cubes, each measuring 1 cm × 1 cm × 1 cm, were put into another beaker and completely covered with distilled water.

At regular intervals for a period of 45 hours, the cubes were removed from the beakers, blotted dry, re-weighed and then replaced into fresh distilled water. The percentage increase in mass was measured for the eight cubes of side 1 cm and the one cube of side 2 cm. The results are shown in the graphs below.

Graph showing readings of cubed potatoes in distilled water and the percentage increase in mass

a) State why eight cubes of sides 1 cm × 1 cm × 1 cm were used in this investigation. [1 mark]

b) i) Name the process which caused the cubes to gain mass. [1 mark]

ii) Describe the process by which the cubes of potato gained mass. [3 marks]

Question courtesy of Eduqas.

a) To keep the volumes the same. You may have also said the volume of the 1 cm3 cubes is the same as the 8 cm3 cubes. [1]

b) i) Osmosis [1]

ii) Water passed in [1] from where it was in high concentration to low concentration/down a gradient [1] via a semi/selectively/partially permeable membrane [1].