chap 36 II

chap 36 II - 1. explain what powers the flow of xylem sap...

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1. explain what powers the flow of xylem sap Xylem sap is powered through cohesion, adhesion, and transpiration. The cohesion of water, due to the hydrogen bonds, allows for movement upwards. Adhesion, similarly, is the ability of the water to stick to the hydrophilic walls of the xylem cells. Tension created by transpiration lowers water potential so that water is able to flow in passively into the stele. Through these combined mechanisms transport of water from roots to leaves can occur by bulk flow, driven by a pressure difference at opposite ends of the passageway. 2. explain this statement: a water potential gradient is not directly responsible for bulk flow, but it is essential for movement of water from the soil to the leaves Without a water potential, there would be no diffusion. Diffusion allows passive movement of water from the soil, through the plant, to the leaves. Bulk flow is the movement of a fluid driven by pressure. Bulk flow, due to pressure difference, is the mechanism of long-distance transport of phloem sap, but it is active transport of sugar at the cellular level that maintains this pressure difference. This water potential gradient allows for the diffusion of water into the roots, and through the plant. 3.
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chap 36 II - 1. explain what powers the flow of xylem sap...

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