Scientists investigated the effect of abscisic acid (ABA) on reducing water loss in plants. The scientists predicted that ABA, as well as stimulating stomatal closure, also reduces water loss in plants in other ways.
The scientists used a mutant variety of thale cress, Arabidopsis thaliana, that has stomata that do not respond to ABA. When ABA is present, the stomata of the mutant variety remain open.
The scientists sprayed different concentrations of ABA on the leaves of the mutant variety and measured the transpiration rates of the plants.
The results are shown in Fig. 2.1.
[Figure 2.1]

Q: What topic does this question test?

This question tests Transport in plants in A-Level Biology (syllabus code 9700). It is worth 7 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Biology Oct/Nov 2025 examination, Paper 5 Variant 2 (9700_w25_qp_52.pdf).

Question

Scientists investigated the effect of abscisic acid (ABA) on reducing water loss in plants. The scientists predicted that ABA, as well as stimulating stomatal closure, also reduces water loss in plants in other ways.
The scientists used a mutant variety of thale cress, Arabidopsis thaliana, that has stomata that do not respond to ABA. When ABA is present, the stomata of the mutant variety remain open.
The scientists sprayed different concentrations of ABA on the leaves of the mutant variety and measured the transpiration rates of the plants.
The results are shown in Fig. 2.1.
[Figure 2.1]

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