Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the 'dead' cells of the xylem work together with the living cells of leaves at the top to keep the water moving?
The living cells of leaves contain stomata in the epidermis, which help in transpiration, meaning the evaporation of water vapours.
This process of transpiration helps in water transportation by creating a transpiration pull in the xylem tissue.
The 'dead' cells of the xylem, specifically the tubular and thick-walled tracheids and vessels, form a continuous hollow pipeline. The transpiration pull generated by the living leaf cells acts on the water column inside these dead tubular cells, pulling the water upwards against gravity from the roots to the plant.
Explanation
The textbook context explains that the living cells in the leaves (epidermis) contain stomata for transpiration (evaporation of water vapours). This transpiration creates a 'transpiration pull' in the xylem. The dead cells of the xylem, namely the tubular tracheids and vessels, provide the structural pathway for this water to be pulled up against gravity. Thus, the living cells generate the pulling force, while the dead cells provide the tubular structure for water transport.