Planning investigations

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   Students plan to investigate the effect of an energy drink on the reaction time of volunteers from their class.

   Describe three ethical issues they should consider and how they would address them.

   Mark scheme

   • Obtain informed consent: tell volunteers what is involved and that they can withdraw at any time (1)
   • Exclude people for whom caffeine could be harmful, e.g. with heart conditions or caffeine sensitivity, and keep the dose low (1)
   • Keep results anonymous / confidential (1)
2. Question 26 marks

   Plan an investigation to find out how light intensity affects the rate of photosynthesis of a freshwater pondweed. Use only standard school laboratory equipment.

   Mark scheme

   • Vary light intensity by placing a lamp at different distances (at least five, e.g. 10–50 cm) from the pondweed, using light intensity $\propto 1/d^2$ (1)
   • Measure the rate by collecting the oxygen produced in a fixed time using a gas syringe / photosynthometer, or by counting bubbles per minute (1)
   • Control temperature using a water bath or a heat shield (e.g. a beaker of water) between the lamp and the plant (1)
   • Control carbon dioxide by adding the same concentration of sodium hydrogencarbonate solution to the water (1)
   • Use the same piece of pondweed and leave it to acclimatise at each new distance for a few minutes before measuring (1)
   • Carry out at least three repeats at each distance and calculate a mean, in a darkened room with no other light sources (1)