A student investigated how the relative humidity of the environment affected the thickness of the waxy cuticle on the leaves of a plant species. The results are shown in the table below.
| Relative humidity of environment (%) | Plant A (μm\mu\text{m}μm) | Plant B (μm\mu\text{m}μm) | Plant C (μm\mu\text{m}μm) | Plant D (μm\mu\text{m}μm) | Mean thickness of waxy cuticle (μm\mu\text{m}μm) |
|---|---|---|---|---|---|
| 35 | 9.2 | 8.8 | 8.1 | 8.7 | 8.7 |
| 55 | 6.4 | 5.8 | 6.1 | 6.5 | 6.2 |
| 75 | 4.3 | 3.9 | 4.1 | 4.5 | 4.2 |
| 95 | 2.1 | 2.5 | 1.8 | 2.0 | 2.1 |
Explain why the mean thickness of the waxy cuticle is lower in environments with a higher relative humidity.
