Water moves into the xylem vessels inside vascular system in the centre of the root; it gets into by using bordered pits. The xylem is inside layered with lignin. This substance is waterproof and it also presents great strength to the xylem vessels, which are tube shaped. A lot of the strength of a plant comes from cells toughened simply by lignin. A Giant Redwood tree is many meters high but water is still able to reach all the cells. Water moves up the xylem for the following reasons.
- Root force gives an initial upward force to water inside xylem vessels. This can be proven by cutting off a shoot near soil level. Some sap will pour vertically out of the xylem of the remaining exposed xylem.
- Water moves up the xylem by capillarity that is the actual up movement of a fluid in a narrow bore tube (xylem has very slim vessels).
- Capillarity occurs because the water compounds have an attraction for each other (cohesion) so when one water molecule moves others transfer with it.
- Capillarity has different component – the point that the water molecules are attracted to the sides of the vessels attracts the water upwards (adhesion).
- Transpiration reasons a very negative water potential in the mesophyll of the leaves. Water in the xylem is of higher water potential and so moves up the xylem.
Xylem vessels die at the end of their maturation stage. The lignin created inside the cells finally results in death. The young xylem cells end to end, finally produce a long tube-like structure (vessel) through which water passes. Xylem can still transfer water after the death of the plant. Mineral ions are also transferred in the xylem.