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← Theoretical B

Q34 — GAPLESS Proteins and Apoplastic Transport in Roots

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

Scientists studied how GAPLESS proteins affect apoplastic transport (transport through cell walls and extracellular space) of nutrients via the endodermis. First, they monitored the penetration of red dye into roots by examining cross-sections at two different positions (depicted as A and B in Figure 1) from the same root of a wild-type plant. Next, they analyzed how GAPLESS proteins affect red dye penetration into roots (Figure 2). In both figures, yellow arrows indicate an endodermal cell layer.

Two fluorescence-microscopy cross-sections of a wild-type root at two different positions, both showing a ring of cells stained red with a yellow arrow indicating the endodermal cell layer; the upper cross-section (position A) shows dye penetrating fully into the central vascular cylinder, while the lower cross-section (position B) shows dye excluded from the dark central vascular cylinder. Figure 1. Cross-sections of a wild-type root at position A (top) and position B (bottom), each with the endodermal cell layer marked by a yellow arrow. Scale bars shown in white.

Two fluorescence-microscopy root cross-sections side by side: wild-type, where red dye is excluded from a dark central vascular cylinder, and a GAPLESS loss-of-function mutant, where red dye has penetrated into the central vascular cylinder; yellow arrows mark the endodermal cell layer in each. Figure 2. Red dye penetration in wild-type versus GAPLESS loss-of-function mutant root cross-sections, both taken at the position-B level. Yellow arrows indicate the endodermal cell layer. Scale bars shown in white.

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

A. The red dye used in the experiment is a small, non-polar molecule.
B. In Figure 1, position B is closer to the root tip than position A.
C. Based on Figure 2, GAPLESS proteins prevent the transport of substances from the cortex to the vascular system via the apoplast.
D. The stem of the plant species used in this study most likely increases in diameter year by year.
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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