Ascent of Sap PDF

 Introduction The Upward movement of water from the root xylem to aerial parts of the plant is Ascent of sap.  Mechanism Transport of water- Theories 1. Vital Theory 2. Root Pressure Theory 3. Physical Force Theory 4. Transpiration Pull and Cohesion-Tension...

 Introduction The Upward movement of water from the root xylem to aerial parts of the plant is Ascent of sap.  Mechanism Transport of water- Theories 1. Vital Theory 2. Root Pressure Theory 3. Physical Force Theory 4. Transpiration Pull and Cohesion-Tension Theory  Vital Theory A common vital force theory about the ascent of sap was put forward by J.C. Bose (1923). It is called pulsation theory. The theory believes that the innermost cortical cells of the root absorb water from the outer side and pump the same into xylem channels.  Root Pressure Theory This theory was put forward by Priestley in 1916. According to this theory the root pressure in the xylem cells helps in the upward movement of water in plants. Root pressure is observed in the certain seasons and maximum in the rainy season. It is 1-2 bars in the maximum water availability. This theory was not accepted because VIZ: a) Root pressure has not been found in all plants ex. in gymnosperms the root pressure is absent but these are the tallest trees in which water moves upwards and reaches upto almost 100m height. b) Root pressure is absent in the unfavorable conditions but ascent of sap continues. c) Water continues to move upward even in the absence of roots. Physical Force Theory Transpiration Pull and Cohesion-Tension Theory https://www.youtube.com/watch?v=9Lpy5jXXJsA Transpiration Pull and Cohesion-Tension Theory