The Apoplast Pathway
This is the movement of water through the APOPLAST- the cell walls and the intercellular spaces. Water fills the spaces between the loose, open network of fibres in the cellulose cell wall. As water molecules move into xylem, more water molecules are pulled through the apoplast behind them due to the cohesive forces between the water molecules. The pull from water moving into the xylem and up the plant along with the cohesive forces between the water molecules creates a tension that means there is a continuous flow of water through the open structure of the cellulose wall, which offers little or no resistance.
The Symplast Pathway
Water moves through the SYMPLAST - the continuous cytoplasm of the living plant cells that is connected through the plasmodesmata - by osmosis. The root hair cell has a higher water potential then the next cell along. This is result of water diffusing in from the soil, which has made the cytoplasm more dilute. So water moves from the root hair cell into the next door cell by osmosis. This process continues until the xylem is reached.
As water leaves the root hair cell by osmosis, the water potential of the cytoplasm falls again, and this maintains a steep water potential gradient to ensure that as much water as possible continues to move into the cell from the soil.