What does transpiration in a plant depend on?

Transpiration in a plant primarily depends on the difference in water vapor concentration between the interior of the leaf and the outside air, which affects the rate at which water is pulled from the roots to the leaves. When the atmosphere around the leaves is drier (lower humidity), water vapor exits the leaf more readily, creating a negative pressure within the leaf cells. This negative pressure facilitates the movement of water from the roots, through the plant, and out into the atmosphere.

The process works effectively because of the cohesion and adhesion properties of water molecules, which help maintain a continuous column of water throughout the plant's vascular system. Therefore, lower water pressure at the top of the plant encourages transpiration by enhancing the pull of water upward from the roots, leading to the desired movement of nutrients and maintaining the plant's turgor.

Understanding this mechanism helps clarify why factors like humidity levels and water pressure at different locations in the plant can influence transpiration rates, but lower water pressure specifically at the top of the plant is a central element of this vital process.