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← Theoretical B

Q33 — PtrWOX4a and PtrVCS2 in Vascular Cambium Proliferation

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Secondary Growth & Wood Anatomy

The vascular cambium is a plant tissue responsible for secondary growth by producing secondary xylem and phloem. Scientists studied how the genes PtrWOX4a and PtrVCS2 affect vascular cambium proliferation in Populus trichocarpa, a eudicot angiosperm species.

Three-panel figure: panel A shows stained stem cross-section micrographs comparing wild-type to PtrVCS2-overexpression and PtrWOX4a-overexpression mutants, with regions A, B, and C labeled and red arrows marking vessel elements; panel B is a photo comparing the height of wild-type Populus trichocarpa plants to two independent PtrVCS2 loss-of-function lines; panel C shows safranin O/fast green-stained stem cross-sections comparing wild-type to a PtrVCS2 loss-of-function mutant, with a scale bar. Figure 1. A Stem cross-sections of wild-type and indicated mutant plants (C denotes vascular cambium layers, and red arrows indicate vessel elements; WT: wild-type, OE: overexpression). B The height of P. trichocarpa wild-type versus PtrVCS2 loss-of-function (LoF) mutants. C How a loss-of-function PtrVCS2 mutation affects the development of secondary vascular tissues in the stem, shown by histological staining with safranin O (red/pink) and fast green, which stain lignified and non-lignified cells, respectively. Scale bar: 1 mm.

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

A. In Figure 1A, cells in Region A are more prone to rupture than cells in Region B.
B. PtrWOX4a and PtrVCS2 have opposing effects in regulating vascular cambium proliferation.
C. PtrVCS2 sets the upper limit for primary and secondary growth.
D. Enhanced vascular cambium proliferation accelerates secondary xylem development.
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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