Question

What happens to the tension in the xylem when the stomata close and evaporation stops? It remains constant the moment the stomata close. It continues to increase until the living cells of the leaf are fully hydrated. It goes to zero once evaporation ceases. It drops to a value closer to that of the water-filled pores in the soil.

Answer 1

The tension in the xylem drops when stomata close and evaporation stops because transpiration, the primary driver of water movement in the xylem, is halted. The negative pressure that pulls water through the plant is reduced, and water is maintained within the plant structures.

Step-by-step explanation:

When the stomata close and evaporation stops, the tension in the xylem drops. This is because transpiration, which is the main driver of water movement in the xylem, is halted. The tension within the xylem is created by the evaporation of water at the leaf-atmosphere interface, leading to a negative pressure that pulls water from the roots up through the plant. This is explained by the cohesion-tension theory of sap ascent. With the closing of stomata during times of low water availability or at night, the loss of water by evaporation ceases, and the cohesive forces of water molecules, along with the adhesion of water to the cell walls, help maintain the water within the plant, reducing the tension previously generated by active transpiration.

Answer 2

Step-by-step explanation:

What occurs when the stomata close and evaporation stops is that, the tension in the xylem continues to increase until the living cells of the leaf are fully hydrated. This happens according to the cohesion-tension theory of sap ascent.

This happens at night. Transpiration stops immediately when the stomata is closed. There is a cohesion between each water molecule and adhesion between the water molecules and the stem walls; water is held in the leaves ad stems when the stomata is closed this hereby increases the tension.