Describe the transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
Transpiration pull theory: The theory was put forward by Dixon and Jolly. The main features of the theory are : (i) There is a continuous column of water (present in the tracheary element) from the root through the stem and into the leaves. (ii) Water molecules attached to one another, by cohesion force, adhesion force (between their walls and water molecules), and surface tension. (iii) The water in the tracheary element would come under tension, due to transpiration also called transpiration pull Factor affecting transpiration: External factors e.g. atmospheric pressure, temperature, humidity, CO2, sunlight, wind velocity, etc. The thickness of cuticle, number, position and closing and opening of stomata, pH, and hormones are internal factors which affect transpiration. Significance of transpiration: Ascent of sap Removal of the excess water Cooling effect Distribution of minerals. Transpiration supplies water for photosynthesis.
