If there is a break in the water column or chain, since it's under tension, the broken end snaps up into the xylem and continuity is lost. It cannot be reestablished, that tube can no longer carry water. As the column of water moves through the roots, stem and leaves, nutritional elements are carried with it to the leaves. It is decreased when solutes are present. A cell has a lot of dissolved sugars in it.
Water surrounding the cell has fewer solutes.
The movement of water into a cell because of differences in solute concentration inside and outside the cell is called osmosis. Osmotic potential is called As water enters a cell it swells and pressure increases in the cell because the membranes and wall enclosing the cell prevent the cell from expanding indefinitely. Pressure increases created by pressure is called Eventually the increase in pressure raises the potential to the point that it equals that of water outside the cell and there is no net uptake of water into the cell. Water can still move in and out, but the rate is the same in either direction. The water potential of a cell is the combination of the water potentials of osmosis and pressure.