Measurements of the Diameter of a Plant Stem During a Long

Multiple Choice

Measurements of the diameter of a plant stem during a long drought show a gradual decrease in diameter over time and then a sudden return to almost its original diameter, even as the drought continues. Which of the following hypotheses is the MOST likely explanation for the increase in stem diameter?

A) Water flow from the soil increased due to the use of ATP to drive the selective uptake of nutrients, leading to water uptake by osmosis.
B) Water flow from the soil increased due to greater stomatal opening.
C) Air entry and cavitation released the tension in the stem xylem.
D) Redistribution of water from the leaves swelled the stem xylem.