Calculate the mean stomatal density in the three fields of view in Figure 9.

Give your answer as number of stomata per mm2

Show your working.

Stomatal density ______________ per mm2

The scientists used leaves from individual trees that had grown in different areas of the world in different years. Each tree had grown in an area and year with known carbon dioxide concentration.

Their results are shown in Figure 10.

Give a null hypothesis for this investigation and name a statistical test that would be appropriate to test your null hypothesis.

Null hypothesis

Statistical test

From 1910 to 2000, the carbon dioxide concentration in the atmosphere increased from 300 parts per million to 365 parts per million.

Use Figure 10 to calculate the mean rate of change in stomatal density from 1910 to 2000.

Give your answer as number of stomata per mm2 per 10-year period.

Show your working.

Number of stomata per mm2 per 10-year period

A journalist saw Figure 10 and suggested that future increases in atmospheric carbon dioxide concentration could result in less transpiration.

Evaluate his suggestion.