Explain7 marksChallenge
A researcher investigating water transport in a 60 m tall Douglas fir tree measured the diameter of the trunk at 1.5 m above ground every hour during a clear summer day. She found that the trunk diameter decreased slightly from early morning until mid-afternoon, then increased again in the evening. The maximum daily decrease in diameter was 2.3 mm. She also measured the rate of transpiration from the leaves and found it peaked at midday.
Explain how the properties of water and the structure of the xylem enable water to be transported from the roots to the top of the tree against gravity, and explain how the observed changes in trunk diameter relate to the cohesion-tension mechanism.