Lichens grow on the bark of trees. Different species of lichen have different tolerances to sulfur dioxide, an air pollutant.
Scientists recorded the number of lichen species growing on trees at different distances from the centre of a city. They also measured the concentration of sulfur dioxide in the air at each distance.
The Figure shows the results.
Figure
[Image brief: Line graph with two y-axes on a plain white background with light grey gridlines. x-axis titled "Distance from the city centre in km", from 0 to 12, with gridlines every 1 km and numbered every 2 km. Left y-axis titled "Number of lichen species", from 0 to 20, numbered every 2. Right y-axis titled "Concentration of sulfur dioxide in µg per m³", from 0 to 70, numbered every 10. Solid line labelled "lichen species" (read against the left axis) passing smoothly through (0, 1), (2, 2), (4, 5), (6, 9), (8, 14), (10, 16), (12, 17). Dashed line labelled "sulfur dioxide" (read against the right axis) passing smoothly through (0, 60), (2, 52), (4, 40), (6, 28), (8, 16), (10, 10), (12, 8). Small dots at each data point on both lines. A small key in the top centre shows "solid line = number of lichen species" and "dashed line = sulfur dioxide concentration". No other labels.]
Describe the relationship between the concentration of sulfur dioxide and the number of lichen species.
Explain why the number of lichen species can be used as evidence of the level of air pollution.
Discuss the use of lichens to assess air quality, compared with measuring sulfur dioxide with an electronic meter.
Blackspot is a fungus that infects the leaves of roses. Blackspot is sensitive to sulfur dioxide.
Explain why roses near the city centre are less likely to have blackspot.
44 exam-style questions on Edexcel GCSE Biology 9.3 Material cycles and decomposition, covering 9.3.1 Cycling of materials through ecosystems, 9.3.2 The carbon cycle, 9.3.3 The water cycle, 9.3.4 The nitrogen cycle, 9.3.5 Indicator species and pollution, 9.3.6 Decomposition in preservation and composting, and 9.3.7 Rate changes in decay of biological material. Each one has a worked solution and a mark scheme showing where the marks go.