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The primary purpose of transpiration in plants:

The loss of water in the form of water vapours through aerial parts of plant like stomata, lenticels, cuticle. Mostly it occurs through stomata, nearly 90% of water are evaporated. It helps in:

• It helps in absorption and upward movement of water or ascent of sap in xylem.
• It also helps in regulation of temperature.

➤ The Transpiration creates a pull which helps in the absorption and upward movement of sap(water and minerals) to reach the upper parts of the plant.

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The water absorbed along with minerals from the soil is known as Sap. We can say that, it is the dilute solution of minerals. Their upward movement is known as ascent of sap or conduction of water.

But how, it reaches the upper parts against gravity?

• Many external agents are involved in such phenomenon like Root pressure, Capillary force, Adhesion and Transpirational pull.
• The main force responsible for upward movement of water and minerals is Transpirational pull.
• The water evaporates, and the cell is now in need of water, so it will take water from its adjacent cell. That cell will again take water from adjacent one. Similarly, this chain tooks place and finally the last cell absorb water from roots.
• A continuous column of water through the stem is maintained due to Cohesive force i.e attraction between similar molecules.

Path of ascent of sap

Water from soil ➝ Root hairs ➝ Epiblema ➝ Cortex ➝ Endodermis ➝ Pericycle ➝ Xylem vessels.

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