Apoplast And Symplast Pathways In A Root Hair

Plants take in water from the soil, along a concentration gradient, through uncutinized epidermal cells of their roots. Near the root tips (where most of the water is absorbed), these cells greatly increase their absorptive areas by extensions called root hairs. As water enters the cell (hair), it can take one of two routes depending upon whether or not it has entered the cytoplasm of the cell. These routes are called the APOPLASTIC and SYMPLASTIC pathways.APOPLASTIC PATHWAY
Because cellulose, the principal constituent of the cell wall, absorbs water like a sponge (think 'cotton wool'), water can travel from cell to cell - along with any solutes dissolved in it - via these cell walls WITHOUT crossing the plasma membrane to enter the cytoplasm of any cell. This is the APOPLASTIC pathway.

SYMPLASTIC PATHWAY
Water can also cross BOTH the cell wall AND the plasma membrane to enter the cytoplasm, then travel from cell to cell via the plasmodesmata in the cell walls. This route is called the SYMPLASTIC pathway. Because the plasma membrane is partly permeable, entry to the cytoplasm must be by OSMOSIS.

NUTRIENT SELECTIVITY

• There is a misconception that nutrients enter root hairs in solution. This is not strictly correct - it only applies to the apoplastic pathway, where the plasma membrane need not be crossed.
• However, in the symplastic pathway, both water and minerals (nutrients) must each cross the plasma membrane by a separate and independent process; one is PASSIVE the other ACTIVE.
• Water passes passively by osmosis.
• Minerals, on the other hand, must pass through the plasma membrane by ACTIVE TRANSPORT, a selective process.
  

See also: 'How Water Enters A Plant: Apoplast And Symplast Pathways'