DBQ p.128- Water Permeance of Waxy Cuticle
1) Generally, as the temperature increases, the permeance of the cuticle increases as well. However, as the increasing permeance of the cuticle, its rate of increase also increases. This is true for all species, but the Liriodendron’s rate increases the earliest (the earliest, noticeable change in rate is seen from 45˚C to 50˚C) and fastest (at 55˚C, the permeance reaches nearly 18 x 10^6/ ms^-1).
2) As the plant’s permeance increases with the temperature, it will become more prone to water loss. This will also cause transpiration to be halted by the stomata by closing the openings (water deficiency causes the synthesis of of abscisic acid, closing the stomata). However, because this experiment uses four species that might not be adapted for the same environments, these consequences would differ. Species that show very high permeance and rate of permeance are probably adapted to environments where high temperatures are uncommon, while those with low permeance and steady rate of permeance are adapted to life in hotter climates.
3a) 1.2 µm
3b) 1.7 µm
4) The data shows various anomalies like the cuticle with the highest permeance (1.2 µm cuticle with a permeance of nearly 6 ms^-1) and the trend is not clear like the fact that the cuticles showing the highest and lowest permeance of water is only about 0.5 µm difference in thickness. Nor does it help to have a small sample size of cuticle wax thicker than 2 µm (most of the cuticular wax is 0-2 µm thick), because it makes the last three data points extremely unreliable (we cannot be sure if these points are anomalies or not). Also, cuticular waxes thinner than 2 µm show the highest permeances out of the whole experiment, and this permeance drops to close to 0 for the cuticular wax with thickness of about 3.1 µm. Thus, even with the increasing trend in permeance for water in cuticular waxes thicker than 3 µm, the data does not show a clear trend and is lacking trials and sample size to be able to draw any conclusions for them, allowing us to reject this hypothesis for now. With further investigations, it may become clearer if there is a relationship between these two variables or not.
14liedan 