Transpiration stream

The main driving factor is the difference in water potential between the soil and the substomatal cavity caused by transpiration.

It allows for plants to efficiently transport water up to their highest body organs, regulate the temperature of stem and leaves and it allows for upstream signaling such as the dispersal of an apoplastic alkalinization during local oxidative stress.

The long and thin shape of root hairs maximizes surface area so that more water can enter.

There is greater water potential in the soil than in the cytoplasm of the root hair cells.

There is also a pressure change between the top and bottom of the xylem vessels, due to water loss from the leaves.

Overview of transpiration.
1-Water is passively transported into the roots and then into the xylem .
2-The forces of cohesion and adhesion cause the water molecules to form a column in the xylem.
3- Water moves from the xylem into the mesophyll cells, evaporates from their surfaces and leaves the plant by diffusion through the stomata.