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← Theoretical A

Q35 — Sequoia Tree Water Use Strategies

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Water Transport & Transpiration

Fluid dynamics put an upper limit on how high a tree’s water column might exist, and above that limit, water transport in the xylem will be disrupted. However, trees similar to Californian redwoods routinely grow above this limit. Scientists studied Californian Sequoia sempervirens from the alluvial flood plain and Sequoiadendron giganteum from the mountain slopes with most likely dry soil. Xylem adaptations have higher water and carbon cost upfront than stomatal adaptations, but allow plants to transpire more.

PCA-style scatter plot of tree water-use traits, where PC2 separates efficient stomatal water use from efficient xylem water use, PC3 is inversely proportional to leaf mass and wood density, and symbol size indicates tree height. Figure 1. Plots like the one above condense many variables like leaf conductance and wood density into two categories. Low PC2 values correspond to more efficient stomatal water use, and high PC2 to more efficient xylem water use. PC3 values are inversely proportional to leaf mass and wood density. The bigger the symbol, the taller is that particular tree. Middle-size symbols are a different shape to make telling apart easier.

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

A. S. giganteum wood is on average denser than S. sempervirens wood.
B. Short S. sempervirens trees are more adapted to resist xylem blockage.
C. S. giganteum might have higher PC2 scores if it is irrigated for several generations.
D. S. sempervirens wood density has a strong negative correlation with height.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)