Cohesion Hypothesis
The cohesion-tension theory postulated by John Joly and Henry Horatio Dixon in 1894 explains the intermolecular attraction observed in the process of upward movement of water molecules through the xylem of plants against gravity. According to this theory, the transpiration pull occurs in the following ways:
- Roots absorb the water from the soil due to lower water potential in the roots than soil.
- The mesophyll cells of leaves have a continuous thin layer of existing water which evaporates from the intercellular spaces by transpiration.
- An air-water interface occurs in between cellulose microfibrils and mesophyll cells creating small spaces.
- The continuous evaporation of water creates tension in the water column. This water column does not collapse due to high tensile strength.
- This surface tension in the water column helps in drawing the water from the nearby cells.
- Thus, the water potential reduces in the roots than the atmosphere which causes the water to diffuse into the surrounding air and further creates a suction force or transpiration pull.
- So, it can be concluded that the water from the soil enters the roots due to lower water potential, and then the water is drawn up to the xylem by cohesive and adhesive forces. Then the water molecules form a column throughout the xylem vessels due to transpiration and are released through the stomata of leaves as water vapors to the atmosphere.
Transpiration Pull in Plants
An overview of transpiration pull in plants describes the details of transpiration pull, a physiological process that helps the plants pull the water from the soil to the leaves by a force generated within the xylem. This process starts when the stomatal opening of the leaf allows water and carbon dioxide to enter the plant.
As photosynthesis happens, water vapor is released through the leaf, causing a drop in air pressure within the leaf. This negative air pressure aids the water molecules to reach the leaf through the stem. In this article, we will look into transpiration pull – meaning, phenomenon, factors affecting, and significance of transpirational pull in plants.
Table of Content
- What is Transpiration?
- What is the Transpirational Pull?
- Cohesion Hypothesis
- The Phenomenon of Transpiration Pull in Plants
- Role of Transpiration Pull in Plants
- Conclusion – An Overview of Transpiration Pull in Plants
- FAQs on Transpiration Pull in Plants