Which of the Following Does Not Support the Cohesion- Tension

Question

Which of the following does not support the cohesion- tension theory of xylem transport?
A) Following cutting of a petiole, the xylem sap withdraws from the cut edge toward the blade of the leaf.
B) Measurements using a root bomb and xylem pressure probe detect negative pressures in xylem tissue.
C) Following application of a respiration inhibitor to a plant, xylem transport decreases substantially.
D) Dendrograph measurements detect small daily changes in the diameter of tree trunks.
E) Pressure bomb measurements detect daily changes in the water potential of leaf tissue.

Accepted Answer

The cohesion-tension theory explains that water is pulled through the xylem from roots to leaves due to the cohesive and adhesive properties of water molecules. A respiration inhibitor would not directly affect this process, so a substantial decrease in xylem transport following its application does not support the cohesion-tension theory. The other options do support the theory in different ways (A - capillary action, B - negative pressure, D - changes in trunk diameter due to water uptake, E - changes in leaf water potential due to transpiration).