Cells in contact with the soil actively take up ions at the roots, creating a concentration difference. Water moves into the root xylem from the soil to eliminate this difference, establishing a steady upward flow.
What creates a difference in ion concentration between the root and the soil, and how does this affect water movement into the root xylem?
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The difference in ion concentration between the root and the soil is created by the active uptake of ions by root cells in contact with the soil. Root cells actively transport ions from the soil into the root, creating a higher concentration of ions within the root compared to the surrounding soil. This ion gradient establishes an osmotic potential that causes water to move into the root cells from the soil, aiming to equalize the concentration. As a result, water is drawn into the root xylem, contributing to a continuous flow that ultimately leads to the upward movement of water through the xylem vessels in the plant.