Transport through Xylem a. Movement of fluid through the vascular tissue of plan

Question

Transport through Xylem

a. Movement of fluid through the vascular tissue of plants is often expressed using water potentials. What does the negative sign tell you about a cells water potential?

b. What two processes or events taking place in the plant generate the very negative water potentials typically observed in the leaves?

c. Horticulturists sometimes talk about harvesting xylem sap when the sap is flowing. Identify two environmental conditions that could slow down or stop the flow of xylem sap through a tree.

d. The leading theory describing the movement of sap through xylem is call the cohesion-tension theory.

i. What does the cohesion part of the theory refer to (explain).

ii. What does the tension part of the theory refer to (explain).

Explanation / Answer

Evaporation of water from leaves exerts negative pressure on plant to pull water upwards. During evaporation, some amount of water in mesophyll cells of the leaf gets evaporated. The remaining water is collected in the cell wall to form air interfaces. The water that has reached to the surface of the leaf form a curvature due to negative pressure or tension. This process of substantial movement of water in the plant is explained in the theory of Cohesion-tension.

Conduction of water and nutrients and translocation of organic materials from sites of synthesis to storage sites.

Deserts and subarctic areas

I) Cohesion refers to upward pulling of water against gravitational force.

II) Tension refers to the pressure exerted on the water.

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