A student investigated the anatomical adaptations of English ivy (Hedera helix) leaves to different environmental conditions. They sampled five leaves from a north-facing, heavily shaded brick wall and five leaves from a south-facing, sunny brick wall, measuring the total leaf thickness using a digital micrometer.
| Leaf | Thickness on shaded north-facing wall (μm\mu\text{m}μm) | Thickness on sunny south-facing wall (μm\mu\text{m}μm) |
|---|---|---|
| 1 | 140 | 210 |
| 2 | 132 | 195 |
| 3 | 145 | 205 |
| 4 | 138 | 212 |
| 5 | 145 | 208 |
| Mean | 140 | 206 |
Explain the difference in the mean thickness of ivy leaves found on the sunny south-facing wall compared to those on the shaded north-facing wall.
