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Q32 - Turgor Pressure and Tissue Layer Mechanics in Explosive Seed Dispersal

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Plant Stress Physiology & Defense

In some plants, fruit valves bend and/or coil explosively to disperse seeds. While dehydration typically triggers this in many species, fruit valves of Cardamine hirsuta instead bend and coil explosively upon mechanical stimulation when the fruits are fresh and turgid. Researchers tested bending of living intact fruit valves (all layers combined) in air, pure water, and 4 M NaCl solution; bending of freeze-thaw-killed valves in water; and bending of living valves separated into outer-layer-only or inner-layer-only in water. Results (Table 1): all layers combined, living, in air: no bending. All layers combined, living, in water: strong bending. All layers combined, living, in 4 M NaCl: no bending. All layers combined, killed, in water: no bending. Outer layer only, living, in water: bending, and it shrank longitudinally. Inner layer only, living, in water: little bending, and its length was unchanged.

Explosive bending and coiling of a fruit valve of C. hirsuta To study how the fruit valve of C. hirsuta builds up energy for bending, researchers examined effects of various treatments and conditions on the bending of fruit valves (Table 1). Explosive bending and coiling of a fruit valve of C. hirsuta To study how the fruit valve of C. hirsuta builds up energy for bending, researchers examined effects of various treatments and conditions on the bending of fruit valves (Table 1).

Using the information and data, determine which of the statements are true or which are false.

A, B, C fill-in. Choose the most appropriate answer set to fill in the blanks: Higher turgor pressure leads to (A) bending of a fruit valve in C. hirsuta. A shallow cut made on an intact fruit valve in the (B) direction would cause the cut to open immediately. The outer layer cells of fruit valves are (C) in water as compared to those in air.
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Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)