Q42 - Day-Night Oxygen and Ethanol Cycling in Eelgrass Roots
Eelgrass (Zostera marina) is a submerged marine plant. During the daytime, O₂ is transported via the aerenchyma of the green parts and rhizomes out into the roots, and an oxygen-rich zone develops in the surrounding anoxic sediment. At nighttime it is a different story: now ethanol diffuses out of the roots and into the sediment (Fig.).
Eelgrass at day and night, and cross-sections of leaf and root.
Figure 1.
Figure 2.
Using the information and data, determine which of the statements are true or which are false.
A. For respiratory reasons, Zostera roots are expected to have a thin epidermis
B. Both at day and night, O₂ readily diffuse into the roots
C. Root uptake of nutrients is independent of time of day
D. At nighttime, the concentration of Na⁺ is expected to decrease in root cells
Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)