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← Theoretical B

Q32 — Venus Flytrap Closure: Temperature and Chemical Effects

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Tropisms & Nastic Movements

Venus flytrap is a carnivorous plant. In an experiment, researchers measured how Venus flytraps close at different temperatures (Figure 1A and Figure 1B) and in response to electrical stimulation (Figure 1C). The soil was treated with substance A for 4.5 hours before the electrical stimulation (curve 3, Figure 1C). After that, soil in the vicinity of the Venus flytrap was washed several times with distilled water (curve 4, Figure 1C).

Four-panel graph of Venus flytrap closure kinetics: panel A shows normalized trap-closure distance over time for two curves (1 and 2), with an inset photo of a trap mid-closure; panel B shows closure speed at 20°C and 36°C; panel C shows closure speed for curves 3 (during substance A treatment) and 4 (after washing out substance A); panel D shows the leaf’s respiration rate over time after repeated trigger-hair stimulation, with two arrows marking stimulation onset and offset. Figure 1. For A, B, C: X — time (s) after stimulation. A Trap closure after an electrical stimulation at temperatures 20°C and 36°C; Y = y/ymax, where ymax is the trap’s maximally open distance. B The same data from graph A, showing temperature’s influence on the speed of trap closure; Y = speed (1/s). C Trap-closure speed due to electrical stimulation; Y = speed (1/s). D Y = rate of respiration (µmol/m²·s) in the trap leaf due to repeated trigger-hair stimulation in already-closed traps; X = time (s). Arrow = stimulation begins, blunted arrow = stimulation ends.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. On graph A curve 1 is obtained under 20°C, while curve 2 is under 36°C
B. The effect of substance A is irreversible
C. Substance A delays the trap closure but does not affect the speed of the closure
D. Graph D shows that there are several causes of increased respiration aside from energy expenditure for trap closure.
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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF