What is the meaning of water vapor from leaves?

Water enters the plant organism through the roots. Together with water, mineral salts are absorbed, which are necessary for growth and development. From the root through the vessels, these solutions rise up and enter all the organs of the plant.

It is known that some of the water is evaporated by the leaves. This process is called transpiration. What is its significance?

Firstly, transpiration is protection against overheating. Photosynthesis requires light. And light is not only energy, but also heat. To prevent the leaf from overheating, water evaporates through the stomata – special structures of the skin, and the surface temperature decreases.
Secondly, this process facilitates the movement of solutions through the vessels. After all, if the water does not decrease, then when the vessels are filled to the top, its movement will stop (as in water pipes with the tap closed).