Exchange surface responsible for water and mineral absorption (reduce waterloss from transpiration)

Long thin extention of root epidermal cell 

Function for a few weeks then die and are replaced nearer the site of growth

Efficient as:

Large S.A and occur in 1000's

Thin surface layer do materials can move more easily

Occur behing tips of young roots

Hairs grow into spaces around soil particles  

Damp = surrounded by soil solution containing minerals

Soil solution mostly water so water potential slightly less than 0

Root hairs and cells have sugars, amino occids and mineral ions dissolved in them = much lower water potential

Water moves in by osmosis down a water potential gradient

Two journies across the root - symplastic and apoplastic pathway

Water drawn into endodermal cells

Pulls more water behind it as cohesive properties

Creates tension that draws water along cell wall of root cortex cells

Cellulose cell wall has many water-filled spaces so little resistance to this pull of water

In cytoplasm as a result of osmosis

Passes through plasmodesmata (tiny openings in cell wall)

Each filled with tiny cytosplasm strand

Continuous column of cytoplasm from root hair cell to xylem

Moves along this column

Water enters by osmosis increasing the water potential of the root hair cell

Root hair cell has higher water potential than 1^st cortex cell

Water moves to 1^st cortex cell down water potential gradient by osmosis

1^st cell has higher water potential than neighbouring cell to the inside - water moves to neighbouring cell

Neighbouring cell higher water potential than 2^nd neighbouring cell 

Water moves into 2^nd neighbouring cell

Water loss from 1^st cortex cell lowers its water potential

Water moves from root hair cell into 1^st cortex cell

Water potential gradient across whole cortex

Carries water along cytoplasm from the root hair cell to the endodermis