Hydrophytes are aquatic plants which are adapted to living in very wet environments.
Water lilies are an example of a hydrophyte which has evolved to show higher rates of transpiration in order to support their growth in garden ponds.
Some adaptations of water lilies include the following:
A thinner or absent waxy cuticle
Stomata on the upper side of the leaf
Large flat leaves
Use the image above and your knowledge of plant leaf structure and transpiration to explain how these adaptations may help to maximise the rate of transpiration in hydrophytes.
Terrestrial plants will often not survive if they are surrounded by water in the same way as the hydrophytes described in part c). Flooding of crop fields has become a severe problem in the US with detrimental effects on the growth of crop plants such as potatoes and beans. Crops growing in flooded soil are unable to absorb sufficient amounts of water through their roots, leading to wilting of their leaves.
Explain why, in the event of a flood, the uptake of water into the root cells may be reduced.
The scientist who carried out the investigation in part a) concluded from his data that water moves through the xylem through the cohesion tension mechanism.
Evaluate his conclusion based on the validity of the evidence provided by the results of this investigation.
Some students were investigating the effect of capillary tube diameter on the uptake of water by capillary action.
They set up three capillary tubes with diameters of 0.6 mm, 0.8 mm and 1.0 mm and measured the distance moved by water in 30 seconds. Their results can be seen below:
The graph shows the differences in water movement in the xylem of a tree. The measurements were taken in the branches at the top of the tree and in the trunk of the tree.
Using ideas illustrated by the capillary model in part a), explain the results shown in the graph.
The students set up a potometer with a 0.8 mm diameter capillary tube to measure the rate of transpiration in a branch removed from a tree. Over a period of 30 minutes, the students noted that the bubble moved 13.7 cm.
Calculate the rate of transpiration shown by the leaf in mm3hr-1. Use the equation πr2 to calculate the area of a circle.
Some adaptations of water lilies include the following:
