Root hair cells

A diagram of the root epidermal cell

The root hairs are where most water absorption happens. They are long and thin so they can penetrate between soil particles and they have a large surface area for absorption of water.

Water passes from the soil water to the root hair cell's cytoplasm by osmosis. This happens because the soil water has a higher water potential than the root hair cell cytoplasm:

SolutionWater concentrationConcentration of dissolved solutes
Soil waterHighLow
Root hair cell cytoplasmLowHigh

Root hair cells - Higher

To maintain the concentration gradient and so the constant movement of water into the root hair cell by osmosis, the root hair cell actively transports mineral salts into the cell.

This means it uses energy - these cells are actively respiring in order to move mineral salts from low concentration outside of the cell to the high concentration in the cell. Thus ensuring osmosis and the transpiration stream continues.