Experimental Setup of Transpirational Pull

Transpiration signifies the release of water in vapour form from the above-ground parts of the plants. This process generates an upward suction force due to a continuous water column. This column, formed by water’s cohesive and adhesive attributes, originates from the mesophyll cells in the leaves (where water is lost) and extends to the root hairs (where water is taken in). This force, termed transpiration pull, plays a pivotal role in water and mineral uptake and upward movement within the stem.

Experitment Procedure

To demonstrate the experiment on transpirational pull, we need to follow the given procedure:

Securely insert a graduated 1 mL pipette into one end of a rubber tube, and ensure that it fits tightly.
Choose a suitable twig with the appropriate diameter and size, then cut it obliquely using a knife, being cautious not to damage the bark.
Moisten the cut surface using water.
Fill the rubber tube and pipette with water by the suction force.
Introduce the twig to the opposite end of the rubber tube and fasten it tightly with a thread to ensure an airtight seal.
Fix the setup with the help of a burette stand and a clamp.
Take a glass tube or beaker, and pour coloured water (using substances like eosin, methylene blue, or blue ink). Position the pipette’s nozzle within the liquid.
Record the initial level of coloured water within the pipette.
Place the entire arrangement in sunlight or beneath a fan for an hour, and observe the final level of coloured water within the pipette.

Observation

After an hour, a consistent ascent of coloured water occurs within the pipette. This phenomenon arises from the suction force generated by water transpiration through the leaves and subsequent water absorption through the stem’s xylem.

The motion of water, driven by the process of transpiration, establishes a water gradient between the stomata and the spongy mesophyll.

Consequently, this difference triggers a suction force due to low water potential in the leaf airspace of the stomatal pore that allows the mass flow of water from the soil, roots hair, root xylem and ultimately to the leaves.

FAQs on Experimental Setup of Transpirational Pull

Q.1: Define transpiration.

Ans. Transpiration is a process through which the above-ground parts of the plant lose water in the form of vapours.

Q.2: What are the advantages of transpiration in plants?

Ans. Transpiration is important to the plant as it leads to the upward movement of sap due to a suction force and contributes to the plant’s cooling process. It facilitates the dispersion of water to every plant part and aids in removing excess water from the plant.

Q.3: What is a transpirational pull?

Ans. Transpiration pull, also known as suction force, plays a crucial role in pulling water upward from the roots to the leaves. Within the leaves, a portion of water is utilised for photosynthesis, while any surplus water is emitted into the atmosphere via tiny openings known as stomata.

Q.4: What causes the transpirational pull?

Ans. As water evaporates from the leaf surface during transpiration, the cohesive nature of water molecules leads to a pulling effect, causing additional water molecules to rise. This results in an unbroken water column spanning the stem, generating a negative tension or pressure within the xylem. This negative pressure draws water from the roots and soil. The transpirational pull is a significant force responsible for the upward movement of sap, known as the ascent of sap.