Feb 8, 2011

Movement of water from soil to leaves

i) from soil to roots
- water diffuse into the cell of root hairs by osmosis
- concentration of water in the cell is lower than outside the cell/soil
- cell becomes hypotonic to the adjacent cells by osmosis
- osmosis goes on until water molecules reach the xylem vessels

ii) roots up the stem
- transpirational pull draws water upwards
- cohesive forces between water molecules
- adhesive forces between water molecules and the wall of xylem vessels
- generates capillary action

iii) from the leaves to the atmosphere
- water evaporates from the surface of the mesophyll cells into the air spaces/surrounding
- water which is lost, is replaced by water in the xylem by osmosis
- water vapour diffuses out/evaporates into the atmosphere through the stomata