HOW WATER MOVES UP THE STEM

1) ROOT PRESSURE

-water moves from

-a less negative water potential in the soil;

-to a more negative water potential in the roots,

- down a water potential gradient

-via osmosis

-The existence of this gradient

-creates a pressure within the roots

-known as ROOT PRESSURE

-Root pressure is responsible for pushing water up the xylem

2) TRANSPIRATION PULL

-Loss of water

-via evaporation

-from the leaves

-through the stomata

-must be replaced by water coming up from the xylem

-Water molecules are attracted to each other by cohesive forces

-which are strong enough to hold molecules together

-in a long chain or column

-As molecules are lost from the top of the column

-the column is pulled up…