An undergraduate researcher used a bubble potometer to investigate the effect of wind speed on the rate of transpiration in a sprig of Hedera helix (ivy). A mechanical fan was used to generate moving air currents around the shoot.
The table shows the volume of water absorbed by the shoot over a 12-minute period.
| Time (minutes) | Volume of water absorbed (cm3\text{cm}^3cm3) - Fan switched on after 4 minutes | Volume of water absorbed (cm3\text{cm}^3cm3) - Fan not switched on (still air) |
|---|---|---|
| 0 | 0.00 | 0.00 |
| 2 | 0.15 | 0.15 |
| 4 | 0.30 | 0.30 |
| 6 | 0.55 | 0.45 |
| 8 | 0.82 | 0.60 |
| 10 | 1.10 | 0.75 |
| 12 | 1.38 | 0.90 |
Explain why the volume of water absorbed by the ivy sprig was also measured under still air conditions (with the fan switched off).
