Biology 9700 · AS & A Level · Transport mechanisms
Transport mechanisms — practice question
Caryocar brasiliense, a tree species, grows in regions that receive very little rainfall for five months each year. Throughout this prolonged dry season, the trees have mechanisms that lower the transpiration rate. An investigation on C. brasiliense was carried out to discover how the rate of transpiration and the mean water potential of leaf cells changed over $12$ hours in one day during the dry season. The results are shown in Fig. 5.1 A and B.
(a)[2]
Define what is meant by transpiration.
(b)[4]
Using Fig. 5.1 A and B, describe how the mean water potential of leaf cells changed across the $12$ hour period. Suggest explanations for these changes.
(c)[3]
The tree C. brasiliense can survive long dry periods. Many plant species living in low-rainfall areas have features that reduce transpiration rates. Some adaptations lower the water potential gradient for water vapour between the air spaces inside the leaves and the surrounding air. Outline how leaves are adapted to reduce transpiration rates in this way.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Escape of water vapour from aerial parts of a plant” …