7. Transport in plants
A section of Biology, 9700
Listing 10 of 457 questions
The tree species Caryocar brasiliense grows in areas where there is very little rainfall for five months of the year. During this long dry season the trees have mechanisms to reduce the rate of transpiration. An investigation was carried out on C. brasiliense to find out 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 A and B. 06 00 08 00 10 00 12 00 time of day mean rate of transpiration / mmol m–2 min–1 14 00 16 00 18 00 –1.60 06 00 08 00 10 00 12 00 14 00 16 00 18 00 –1.40 –1.20 –1.00 –0.80 –0.60 mean water potential of leaf cells / MPa –0.40 –0.20 0.00 A B Define the term transpiration. With reference to A and B, describe the changes recorded in the mean water potential of leaf cells over the 12 hour period. Suggest explanations for these changes. The tree C. brasiliense is able to survive through long dry periods. Many plant species that live in areas with little rainfall have features that reduce transpiration rates. Some adaptations reduce 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.
9700_w17_qp_23
THEORY
2017
Paper 2, Variant 3
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