What is transpiration pull and root …

Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves.

Transpiration pull is the force which aids in drawing the water upward from roots to leaves. In leaves, some amount of water is used for photosynthesis and excess water is released into atmosphere. Water molecules stick to one another through cohesion forming a column in the xylem. The negative pressure created by transpiration pull exerts a force on the water particles causing their upward movement in xylem.

Root pressure is osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves. Root pressure is caused by active distribution of mineral nutrient ions into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis. Root pressure is caused by this accumulation of water in the xylem pushing on the rigid cells. Root pressure provides a force, which pushes water up the stem to a certain level.

Root pressure is the positive pressure that develops in the xylem sap of the root of plants.

Transpiration pull-Water is mostly pulled due to driving force of transpiration from the leaves.