10 free IB Biology practice questions in the real exam format, covering the official content areas, with an explanation for every answer.
IB Biology Practice Test 3Tutor mode
Question 1 of 10
Interaction and interdependence
Students investigated the effect of hydrogen peroxide concentration (independent variable) on the activity of catalase in potato tissue. Ten potato discs (5 mm diameter, 2 mm thick) were added to 10 cm³ of hydrogen peroxide solution buffered at pH 7.0 in a water bath at 25 °C, and the oxygen released was collected in a gas syringe (dependent variable). The initial rate was found from the gradient of the volume–time graph over the first 20 s. Each concentration was tested three times with fresh discs.
Table 1: Mean initial rate of oxygen release
Hydrogen peroxide concentration / %
Mean initial rate / cm³ s⁻¹ (± SD, n = 3)
0.5
0.05 ± 0.01
1.0
0.10 ± 0.02
2.0
determine from Graph 1
4.0
0.27 ± 0.03
8.0
0.29 ± 0.04
SD = standard deviation of the three replicates.
Which statement describes the effect of hydrogen peroxide concentration on the mean initial rate shown in Table 1?