Chapter 23: Nutrition in Plants
As a plant grows upward toward sunlight, it needs to extract an
increasing supply of water and dissolved mineral ions from the soil.
Xylem tissue of angiosperms includes two types of conducting
cells: Tracheid’s and vessel elements. Xylem sap, a solution of
water and inorganic nutrients flows through the long, thin
conduits formed by these dead cells from the roots to the tips of
The roots of the plants do exert a slight upward push on xylem sap.
The root cells actively pump inorganic ions into the Xylem, and the
roots endodermis holds the ions there. The ions accumulate in the
Xylem, water tends to enter by osmosis, pushing Xylem sap upward
ahead of it. This force is called root pressure, can push Xylem sap
up a few meters. The pulling force is transpiration, which is loss of
water from the leaves and other aerial parts of a plant by
Transpiration and its effect on water movement in a tree.
Water molecules exit the leaf through stomata microscopic pores on
the surface of the leaf.
When the stomata are open, water diffuses out of the leaves
because the surrounding air is usually drier than the inside of the
leaf. Transpiration can pull Xylem sap up the tree because of two
special properties of water: cohesion and adhesion. Both of these