"Root pressure theory" proposes that water from roots is...

Name: Problem 13, Chapter 22: Biology: Concepts and Investigations
Uploaded: 2020-05-20T07:05:14-08:00
Duration: 21 s
Channel: Sam Limsuwannarot
Description: "Root pressure theory" proposes that water from roots is pushed up a stem. Although root pressure sometimes occurs, it does not account for all xylem flow. What evidence would you look for to determine whether water in xylem moves under tension or pressure?

"Root pressure theory" proposes that water from roots is pushed up a stem. Although root pressure sometimes occurs, it does not account for all xylem flow. What evidence would you look for to determine whether water in xylem moves under tension or pressure?

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Key Concepts

Cohesion-Tension Theory

This theory explains that water moves upward in plants due to the cohesive and adhesive properties of water, which allow it to form a continuous column under tension. When water is evaporated from the leaves, a negative pressure (tension) is generated that pulls water upward from the roots.

Root Pressure

Root pressure is the phenomenon where solute accumulation in the roots leads to osmotic water uptake, generating a positive pressure that pushes water upward. While it can contribute to water movement in the xylem, it is generally insufficient to account for the entire process in taller plants.

Xylem Pressure Measurement

One key way to distinguish between tension and pressure in the xylem is by direct measurement of the water potential within xylem vessels. Instruments like pressure probes or the pressure chamber can provide evidence by detecting whether the water column is under negative pressure (tension) or positive pressure.

Cavitation and Embolism

Under high tension, the water column in the xylem is prone to cavitation— the formation of vapor bubbles that impede water flow. Observations of cavitation and the plant's repair responses can indicate that water transport is occurring under tension rather than solely by positive pressure.

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