A conservationist wants to investigate how the percentage cover of a nitrogen-sensitive lichen species changes as the concentration of atmospheric nitrogen dioxide (NO2\text{NO}_2NO2) decreases with distance from a busy dual carriageway into a nature reserve.
Which of the following describes the most suitable sampling method and the correct reason for its choice?
Random sampling using a grid and a random number generator, because it allows the investigator to map the continuous change in lichen cover relative to the NO2\text{NO}_2NO2 gradient.
Systematic sampling using a belt transect laid perpendicular to the road, because it allows changes in lichen abundance to be systematically recorded along a continuous environmental gradient.
Systematic sampling using a belt transect laid perpendicular to the road, because it provides a completely unbiased estimate of the total lichen population size across the entire nature reserve.
Random sampling using a grid and a random number generator, because it ensures that areas with the highest NO2\text{NO}_2NO2 concentrations near the road are excluded from the sample to avoid skewing the data.
44 exam-style questions on OCR GCSE Biology Practical skills. Each one has a worked solution and a mark scheme showing where the marks go.